Document and Entity Information - USD ($) $ in Billions	12 Months Ended
Document and Entity Information - USD ($) $ in Billions	Dec. 31, 2018	Feb. 15, 2019	Jun. 29, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	CLEAN HARBORS INC
Entity Central Index Key	0000822818
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		55,855,142
Entity Shell Company	false
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 2.9

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 226,507	$ 319,399
Short-term marketable securities	52,856	38,179
Accounts receivable, net of allowances aggregating $44,315 and $27,799, respectively	606,952	528,924
Unbilled accounts receivable	54,794	35,922
Deferred costs	18,770	20,445
Inventories and supplies	199,479	176,012
Prepaid expenses and other current assets	42,800	35,175
Total current assets	1,202,158	1,154,056
Property, plant and equipment, net	1,561,978	1,587,365
Other assets:
Goodwill	514,189	478,523
Permits and other intangibles, net	441,875	469,128
Other	18,121	17,498
Total other assets	974,185	965,149
Total assets	3,738,321	3,706,570
Current liabilities:
Current portion of long-term obligations	7,535	4,000
Accounts payable	276,461	224,231
Deferred revenue	61,843	67,822
Accrued expenses	233,405	187,982
Current portion of closure, post-closure and remedial liabilities	23,034	19,782
Total current liabilities	602,278	503,817
Other liabilities:
Closure and post-closure liabilities, less current portion of $9,592 and $6,444, respectively	60,339	54,593
Remedial liabilities, less current portion of $13,442 and $13,338, respectively	107,575	111,130
Long-term obligations, less current portion	1,565,021	1,625,537
Deferred taxes, unrecognized tax benefits and other long-term liabilities	233,352	223,291
Total other liabilities	1,966,287	2,014,551
Commitments and contingent liabilities (See Note 18)
Stockholders' equity:
Common stock, $.01 par value: Authorized 80,000,000 shares; issued and outstanding 56,501,190 and 57,297,978 shares, respectively	558	565
Additional paid-in capital	655,415	686,962
Accumulated other comprehensive loss	(223,371)	(172,407)
Accumulated earnings	737,154	673,082
Total stockholders' equity	1,169,756	1,188,202
Total liabilities and stockholders' equity	$ 3,738,321	$ 3,706,570

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Account receivable, allowances aggregating	$ 44,315	$ 27,799
Closure and post-closure liabilities, current portion	9,592	6,444
Remedial liabilities, current portion	$ 13,442	$ 13,338
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, authorized shares (in shares)	80,000,000	80,000,000
Common stock, issued shares (in shares)	56,847,261	56,501,190
Common stock, outstanding shares (in shares)	56,847,261	56,501,190

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues:
Total revenues	$ 858,204	$ 843,181	$ 849,140	$ 749,778	$ 747,403	$ 755,846	$ 752,788	$ 688,941	$ 3,300,303	$ 2,944,978	$ 2,755,226
Cost of revenues: (exclusive of items shown separately below)
Total cost of revenues	594,857	580,685	583,584	546,425	526,690	519,595	519,803	496,585	2,305,551	2,062,673	1,932,857
Selling, general and administrative expenses									503,747	456,648	422,015
Accretion of environmental liabilities									9,806	9,460	10,177
Depreciation and amortization									298,625	288,422	287,002
Goodwill impairment charge									0	0	34,013
(Loss) income from operations	41,485	65,745	64,353	10,991	27,935	47,663	46,744	5,433	182,574	127,775	69,162
Other (expense) income, net	(4,061)	(996)	846	(299)	(3,305)	(432)	(833)	(1,549)	(4,510)	(6,119)	6,195
Loss on early extinguishment of debt		(2,500)				(1,900)	(6,000)		(2,488)	(7,891)	0
Gain on sale of businesses							31,700		0	30,732	16,884
Interest expense, net of interest income of $2,958, $1,897, and $784, respectively									(81,094)	(85,808)	(83,525)
(Loss) income before (benefit) provision for income taxes									94,482	58,689	8,716
Provision (benefit) for income taxes									28,846	(42,050)	48,589
Net income (loss)	$ 16,431	$ 31,089	$ 30,747	$ (12,631)	$ 84,194	$ 12,058	$ 25,880	$ (21,393)	$ 65,636	$ 100,739	$ (39,873)
Earnings (loss) per share:
Basic (in dollars per share)	$ 0.29	$ 0.55	$ 0.55	$ (0.22)	$ 1.48	$ 0.21	$ 0.45	$ (0.37)	$ 1.17	$ 1.77	$ (0.69)
Diluted (in dollars per share)	$ 0.29	$ 0.55	$ 0.54	$ (0.22)	$ 1.48	$ 0.21	$ 0.45	$ (0.37)	$ 1.16	$ 1.76	$ (0.69)
Shares used to compute earnings (loss) per share — Basic (in shares)									56,148	57,072	57,532
Shares used to compute earnings (loss) per share — Diluted (in shares)									56,340	57,200	57,532
Service revenues
Revenues:
Total revenues									$ 2,709,239	$ 2,398,650	$ 2,280,809
Cost of revenues: (exclusive of items shown separately below)
Total cost of revenues									1,861,975	1,641,798	1,543,210
Product revenues
Revenues:
Total revenues									591,064	546,328	474,417
Cost of revenues: (exclusive of items shown separately below)
Total cost of revenues									$ 443,576	$ 420,875	$ 389,647

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 65,636	$ 100,739	$ (39,873)
Other comprehensive (loss) income:
Unrealized gains (losses) on available-for-sale securities (net of taxes (benefits) of $105, $152, and ($214), respectively)	77	32	(321)
Unrealized loss on interest rate hedge	(9,579)	0	0
Reclassification adjustment for losses on available-for-sale securities and interest rate hedge included in net income (loss) (net of taxes of $0, $79, and $0, respectively)	806	143	0
Foreign currency translation adjustments (including tax benefits of $5.0 million and $16.8 million in 2018 and 2016, respectively)	(42,350)	41,636	40,728
Unfunded pension liability (net of taxes of $42, $38, and $57, respectively)	82	108	159
Other comprehensive income (loss)	(50,964)	41,919	40,566
Comprehensive income (loss)	$ 14,672	$ 142,658	$ 693

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Unrealized gains on available-for-sale securities, taxes	$ 105	$ 152	$ (214)
Reclassification adjustment for gains on available-for-sale securities included in net income, taxes	0	79	0
Foreign current translation adjustments, tax benefit	5,000	0	16,800
Unfunded pension liability, taxes	$ 42	$ 38	$ 57

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net income (loss)	$ 65,636	$ 100,739	$ (39,873)
Adjustments to reconcile net income (loss) to net cash from operating activities:
Depreciation and amortization	298,625	288,422	287,002
Goodwill impairment charge	0	0	34,013
Allowance for doubtful accounts	15,817	7,901	6,907
Amortization of deferred financing costs and debt discount	3,846	3,482	3,537
Accretion of environmental liabilities	9,806	9,460	10,177
Changes in environmental liability estimates	2,147	(195)	(4,254)
Deferred income taxes	19,089	(83,335)	15,184
Other expense (income), net	4,510	6,119	(5,685)
Stock-based compensation	16,792	13,146	10,481
Excess tax benefit of stock-based compensation	0	0	(1,198)
Net tax benefit on stock-based awards	0	0	1,165
Gain on sale of businesses	0	(30,732)	(16,884)
Loss on early extinguishment of debt	2,488	7,891	0
Environmental expenditures	(10,115)	(12,965)	(12,170)
Changes in assets and liabilities, net of acquisitions:
Accounts receivable and unbilled accounts receivable	(79,563)	(33,764)	(15,009)
Inventories and supplies	(26,958)	(5,002)	(16,080)
Other current assets	(7,946)	16,720	(8,036)
Accounts payable	46,915	(10,684)	(3,503)
Other current and long-term liabilities	12,121	8,495	13,850
Net cash from operating activities	373,210	285,698	259,624
Cash flows used in investing activities:
Additions to property, plant and equipment	(193,344)	(167,007)	(219,384)
Proceeds from sale and disposal of fixed assets	15,445	7,124	20,817
Acquisitions, net of cash acquired	(151,023)	(49,227)	(206,915)
Additions to intangible assets including costs to obtain or renew permits	(4,688)	(1,617)	(2,831)
Purchases of available-for-sale securities	(44,772)	(38,342)	(598)
Proceeds from sale of available-for-sale securities	28,723	376	0
Proceeds from sale of businesses, net of transactional costs	0	45,426	47,134
Net cash used in investing activities	(349,659)	(203,267)	(361,777)
Cash flows (used in) from financing activities:
Change in uncashed checks	132	(5,940)	(3,177)
Proceeds from exercise of stock options	0	46	627
Tax payments related to withholdings on vested restricted stock	(3,266)	(3,149)	(2,819)
Repurchases of common stock	(45,080)	(48,971)	(22,188)
Excess tax benefit of stock-based compensation	0	0	1,198
Deferred financing costs paid	(4,027)	(5,718)	(4,031)
Premiums paid on early extinguishment of debt	(1,238)	(6,028)	0
Principal payments on debt	(405,768)	(402,000)	0
Issuance of senior secured notes, net of discount	348,250	399,000	0
Issuance of senior secured notes, net of discount	0	0	250,625
Borrowing from revolving credit facility	50,000	0	0
Payment on revolving credit facility	(50,000)	0	0
Net cash (used in) from financing activities	(110,997)	(72,760)	220,235
Effect of exchange rate change on cash	(5,446)	2,731	4,207
(Decrease) increase in cash and cash equivalents	(92,892)	12,402	122,289
Cash and cash equivalents, beginning of year	319,399	306,997	184,708
Cash and cash equivalents, end of year	226,507	319,399	306,997
Cash payments for interest and income taxes:
Interest paid	89,171	93,174	88,669
Income taxes paid	20,036	18,682	29,255
Non-cash investing activities:
Property, plant and equipment accrued	15,657	16,109	9,214
Transfer of inventory to property, plant and equipment	0	12,641	0
(Payable) receivable for estimated purchase price adjustment	$ (4,032)	$ 0	$ 1,910

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Shares Held Under Employee Participation Plan	Additional Paid-in Capital	Accumulated Other Comprehensive loss	Accumulated Earnings
Beginning balance at Dec. 31, 2015	$ 1,096,282	$ 576	$ (469)	$ 738,401	$ (254,892)	$ 612,666
Beginning balance (in shares) at Dec. 31, 2015		57,593
Increase (Decrease) in Stockholders' Equity
Net income (loss)	(39,873)					(39,873)
Other comprehensive income	40,566				40,566
Stock-based compensation	10,481			10,481
Issuance of restricted shares, net of shares remitted	(2,819)	$ 1		(2,820)
Issuance of restricted shares, net of shares remitted (in shares)		136
Exercise of stock options	627			627
Exercise of stock options (in shares)		22
Repurchases of common stock	(22,188)	$ (4)		(22,184)
Repurchases of common stock (in shares)		(453)
Net tax benefit on stock-based awards	1,165			1,165
Ending balance at Dec. 31, 2016	1,084,241	$ 573	(469)	725,670	(214,326)	572,793
Ending balance (in shares) at Dec. 31, 2016		57,298
Increase (Decrease) in Stockholders' Equity
Net income (loss)	100,739					100,739
Other comprehensive income	41,919				41,919
Stock-based compensation	13,146			13,146
Issuance of restricted shares, net of shares remitted	(3,149)	$ 1		(3,150)
Issuance of restricted shares, net of shares remitted (in shares)		133
Exercise of stock options	46			46
Exercise of stock options (in shares)		2
Shares held under employee participation plan	0		469	(469)
Shares held under employee participation plan (in shares)		(25)
Repurchases of common stock	(48,971)	$ (9)		(48,962)
Repurchases of common stock (in shares)		(907)
Ending balance at Dec. 31, 2017	1,188,202	$ 565	0	686,962	(172,407)	673,082
Ending balance (in shares) at Dec. 31, 2017		56,501
Increase (Decrease) in Stockholders' Equity
Cumulative effect of change in accounting principle	231			681		(450)
Net income (loss)	65,636					65,636
Other comprehensive income	(50,964)				(50,964)
Stock-based compensation	16,792			16,792
Issuance of restricted shares, net of shares remitted	(3,266)	$ 1		(3,267)
Issuance of restricted shares, net of shares remitted (in shares)		160
Repurchases of common stock	(45,080)	$ (8)		(45,072)
Repurchases of common stock (in shares)		(814)
Ending balance at Dec. 31, 2018	1,169,756	$ 558	$ 0	$ 655,415	$ (223,371)	737,154
Ending balance (in shares) at Dec. 31, 2018		55,847
Increase (Decrease) in Stockholders' Equity
Cumulative effect of change in accounting principle	$ (1,564)					$ (1,564)

SIGNIFICANT ACCOUNTING POLICIES

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

SIGNIFICANT ACCOUNTING POLICIES

The accompanying consolidated financial statements of the Company reflect the application of certain significant accounting policies as described below:

Principles of Consolidation

The accompanying consolidated statements include the accounts of Clean Harbors, Inc. and its majority-owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation.

Use of Estimates

The preparation of consolidated financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions, which are evaluated on an ongoing basis, that affect the amounts reported in the Company's consolidated financial statements and accompanying notes. Management bases its estimates on historical experience and on various other assumptions it believes to be reasonable at the time under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities and disclosure, if any, of contingent assets and liabilities and reported amounts of revenues and expenses. Actual results could differ from those estimates and judgments.

Cash, Cash Equivalents and Uncashed Checks

Cash consists primarily of cash on deposit and money market accounts. Marketable securities with maturities of three months or less from the date of purchase are classified as cash equivalents. The Company's cash management program with its revolving credit lender allows for the maintenance of a zero balance in the U.S. bank disbursement accounts that are used to issue vendor and payroll checks. The program can result in checks outstanding in excess of bank balances in the disbursement accounts. When checks are presented to the bank for payment, cash deposits in amounts sufficient to fund the checks are made, at the Company's discretion, either from funds provided by other accounts or under the terms of the Company's revolving credit facility. Therefore, until checks are presented for payment, there is no right of offset by the bank and the Company continues to have control over cash relating to both released as well as unreleased checks. Checks that have been written to vendors or employees but have not yet been presented for payment at the Company's bank are classified as uncashed checks as part of accounts payable and changes in the balance are reported as a financing activity in the statement of cash flows.

Marketable Securities

The Company, through its wholly-owned captive insurance subsidiary, invests in marketable securities consisting of U.S. Treasury securities, corporate notes and bonds and commercial paper. Marketable securities with original maturities greater than three months from the purchase date and remaining maturities less than one year are classified as short-term marketable securities. As of December 31, 2018 and 2017 the Company has recorded total marketable securities and cash equivalents of $61.0 million and $40.2 million, respectively, as shown below (in thousands).

(2) SIGNIFICANT ACCOUNTING POLICIES (Continued)




	December 31, 2018		December 31, 2017
Commercial paper	$	8,126	$	2,048
Total cash equivalents	8,126		2,048

U.S. Treasury securities	10,133		3,855
Corporate notes and bonds	38,036		32,729
Commercial paper	4,687		1,595
Total short-term marketable securities	52,856		38,179
Total financial assets	$	60,982	$	40,227

Realized gains and losses on sales of available-for-sale securities in the years ended December 31, 2018, 2017 and 2016 were immaterial. The majority of the marketable securities have a remaining maturity of less than one year and fair value approximates cost.

Allowances for Doubtful Accounts

On a regular basis, the Company evaluates its accounts receivable and establishes the allowance for doubtful accounts based on an evaluation of certain criteria and evidence of collection certainty including historical collection trends, current economic trends and changes in customer payment patterns. Past-due receivable balances are written off when the Company's internal collection efforts have been deemed unsuccessful in collecting the outstanding balance due.

Credit Concentration

Concentration of credit risks in accounts receivable is limited due to the large number of customers comprising the Company's customer base throughout North America. The Company maintains policies over credit extension that include credit evaluations, credit limits and collection monitoring procedures on a customer-by-customer basis. However, the Company generally does not require collateral before services are performed. No individual customer accounted for more than 10% of accounts receivable or more than 10% of total revenues in the periods presented.

Inventories and Supplies

Inventories are stated at the lower of cost or market. The cost of oil and oil products is principally determined on a first-in, first-out ("FIFO") basis. The cost of supplies and drums, solvent and solution and other inventories is determined on a FIFO or a weighted average cost basis. The Company continually reviews its inventories for obsolete or unsalable items and adjusts its carrying value to reflect estimated realizable values.

Property, Plant and Equipment (excluding landfill assets)

Property, plant and equipment are stated at cost. Expenditures for major renewals and improvements which extend the life or usefulness of the asset are capitalized. Items of an ordinary repair or maintenance nature are charged directly to operating expense as incurred. During the construction and development period of an asset, the costs incurred, including applicable interest costs, are classified as construction-in-progress.

(2) SIGNIFICANT ACCOUNTING POLICIES (Continued)

The Company depreciates and amortizes the cost of these assets, using the straight-line method as follows:



Asset Classification		Estimated Useful Life
Buildings and building improvements
Buildings		20–42 years
Leasehold and building improvements		2–45 years
Camp and lodging equipment		8–15 years
Vehicles		2–15 years
Equipment
Capitalized software and computer equipment		3–5 years
Containers and railcars		8–16 years
All other equipment		4–30 years
Furniture and fixtures		5–8 years

The Company recognizes an impairment in the carrying value of long-lived assets when the expected future undiscounted cash flows derived from the assets, or group of assets, are less than their carrying value. For the years ended December 31, 2018, 2017 and 2016, the Company did not record impairment charges related to long-lived assets.

Goodwill

Goodwill is comprised of the purchase price of business acquisitions in excess of the fair value of the net assets acquired. Goodwill is not amortized but is reviewed for impairment annually as of December 31, or when events or circumstances indicate that the carrying value of the reporting unit may exceed its fair value. Upon adoption of Accounting Standards Update (“ASU”) 2017-04 in the fourth quarter of 2017, if the fair value is less than the carrying amount, a loss will be recorded for the excess of the carrying value of the goodwill over the implied value of the goodwill. Prior to adoption of ASU 2017-04, if the fair value was less than the carrying amount, a Step II goodwill impairment test was performed to determine if goodwill was impaired. The loss, if any, was measured as the excess of the carrying value of the goodwill over the implied value of the goodwill. See Note 8, "Goodwill and Other Intangible Assets," for additional information related to the Company's goodwill impairment tests.

Permits and other intangibles

Costs related to acquiring licenses, permits and intangible assets, such as legal fees, site surveys, engineering costs and other expenditures are capitalized. Other intangible assets consist primarily of customer and supplier relationships, trademarks and trade names, and non-compete agreements. Permits relating to landfills are amortized on a units-of-consumption basis. All other permits are amortized over periods ranging from 5 to 30 years on a straight-line basis. Other intangible assets are amortized on a straight-line basis over their respective useful lives, which range from 5 to 20 years.

Finite-lived intangible assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying value may not be recoverable. When such factors and circumstances exist, management compares the projected undiscounted future cash flows associated with the related asset or group of assets to the carrying amount. The impairment loss, if any, is measured as the excess of the carrying amount over the fair value of the asset or group of assets.

Indefinite-lived intangible assets are not amortized but are reviewed for impairment annually as of December 31, or when events or changes in the business environment indicate that the carrying value may be impaired. If the fair value of the asset is less than the carrying amount, the impairment loss is measured as the excess of the carrying value of the asset over its fair value.

Leases

The Company leases rolling stock, rail cars, equipment, real estate and office equipment under operating leases. Certain real estate leases contain rent holidays and rent escalation clauses. Most of the Company's real estate lease agreements include renewal periods at the Company's option. For its operating leases, the Company recognizes rent holiday periods and scheduled

(2) SIGNIFICANT ACCOUNTING POLICIES (Continued)

rent increases on a straight-line basis over the lease term beginning with the date the Company takes possession of the leased assets.

Landfill Accounting

The Company amortizes landfill improvements and certain landfill-related permits over the estimated useful lives. The units-of-consumption method is used to amortize land, landfill cell construction, asset retirement costs and remaining landfill cells and sites. The Company also utilizes the units-of-consumption method to record closure and post-closure obligations for landfill cells and sites. Under the units-of-consumption method, the Company includes future estimated construction and asset retirement costs, as well as costs incurred to date, in the amortization base of the landfill assets. Additionally, where appropriate, as described below, the Company includes probable expansion airspace that has yet to be permitted in the calculation of the total remaining useful life of the landfill. If it is determined that expansion capacity should no longer be considered in calculating the recoverability of a landfill asset, the Company may be required to recognize an asset impairment or incur significantly higher amortization expense. If at any time the Company makes the decision to abandon the expansion effort, the capitalized costs related to the expansion effort are expensed immediately.

Landfill assets—Landfill assets include the costs of landfill site acquisition, permits and cell construction incurred to date. These amounts are recorded at cost, which includes capitalized interest as applicable. Landfill assets, net of amortization, are combined with management's estimate of the costs required to complete construction of the landfill to determine the amount to be amortized over the remaining estimated useful economic life of a site. Amortization of landfill assets is recorded on a units-of-consumption basis, such that the landfill assets should be completely amortized at the date the landfill ceases accepting waste. Amortization totaled $10.3 million, $9.5 million and $9.7 million for the years ended December 31, 2018, 2017 and 2016, respectively. Changes in estimated costs to complete construction are applied prospectively to the amortization rate.

Landfill capacity—Landfill capacity, which is the basis for the amortization of landfill assets and for the accrual of final closure and post-closure obligations, represents total permitted airspace plus unpermitted airspace that management believes is probable of ultimately being permitted based on established criteria. The Company applies the following criteria for evaluating the probability of obtaining a permit for future expansion airspace at existing sites, which provides management a basis to evaluate the likelihood of success of unpermitted expansions:


•	Personnel are actively working to obtain the permit or permit modifications (land use, state, provincial and federal) necessary for expansion of an existing landfill, and progress is being made on the project.


•	Management expects to submit the application within the next year and to receive all necessary approvals to accept waste within the next 5 years.


•	At the time the expansion is included in the Company's estimate of the landfill's useful economic life, it is probable that the required approvals will be received within the normal application and processing time periods for approvals in the jurisdiction in which the landfill is located.


•	The Company or other owner of the landfill has a legal right to use or obtain the right to use the land associated with the expansion plan.


•	There are no significant known political, technical, legal or business restrictions or issues that could impair the success of such expansion.


•	A financial feasibility analysis has been completed and the results demonstrate that the expansion will have a positive financial and operational impact such that management is committed to pursuing the expansion.


•	Additional airspace and related additional costs, including permitting, final closure and post-closure costs, have been estimated based on the conceptual design of the proposed expansion.

As of December 31, 2018, there was one unpermitted expansion at one location included in the Company's landfill accounting model, which represented 16.2% of the Company's remaining airspace at that date. If actual expansion airspace is significantly different from the Company's estimate of expansion airspace, the amortization rates used for the units-of-consumption method would change, therefore impacting the Company's profitability. If the Company determines that there is less actual expansion airspace at a landfill, this would increase amortization expense recorded and decrease profitability, while

(2) SIGNIFICANT ACCOUNTING POLICIES (Continued)

if the Company determines a landfill has more actual expansion airspace, amortization expense would decrease and profitability would increase.

As of December 31, 2018, the Company had 11 active landfill sites (including the Company's two non-commercial landfills), which have estimated remaining lives (based on anticipated waste volumes and remaining highly probable airspace) as follows:



		Remaining Lives (Years)	Remaining Highly Probable Airspace (cubic yards) (in thousands)
Facility Name	Location	Remaining Lives (Years)	Permitted	Unpermitted	Total
Altair	Texas	3	311	—	311
Buttonwillow	California	21	6,234	—	6,234
Deer Park	Texas	4	141	—	141
Deer Trail	Colorado	28	1,755	—	1,755
Grassy Mountain	Utah	51	194	4,830	5,024
Kimball	Nebraska	9	190	—	190
Lambton	Ontario	64	4,821	—	4,821
Lone Mountain	Oklahoma	18	4,124	—	4,124
Ryley	Alberta	7	906	—	906
Sawyer	North Dakota	87	3,522	—	3,522
Westmorland	California	64	2,732	—	2,732
			24,930	4,830	29,760

At December 31, 2018 and 2017, the Company had no cubic yards of permitted, but not highly probable, airspace.

The following table presents the remaining highly probable airspace from January 1, 2016 through December 31, 2018 (in thousands of cubic yards):



	2018		2017		2016
Remaining capacity at January 1,	31,113		32,228		29,786
Changes in highly probable airspace, net	(223	)	—		3,464
Consumed	(1,130	)	(1,115	)	(1,022	)
Remaining capacity at December 31,	29,760		31,113		32,228

Amortization of cell construction costs and accrual of cell closure obligations—Landfills are typically comprised of a number of cells, which are constructed within a defined acreage (or footprint). The cells are typically discrete units, which require both separate construction and separate capping and closure procedures. Cell construction costs are the costs required to excavate and construct the landfill cell. These costs are typically amortized on a units-of-consumption basis, such that they are completely amortized when the specific cell ceases accepting waste. In some instances, the Company has landfills that are engineered and constructed as "progressive trenches." In progressive trench landfills, a number of contiguous cells form a progressive trench. In those instances, the Company amortizes cell construction costs over the airspace within the entire trench, such that the cell construction costs will be fully amortized at the end of the trench useful life.

The design and construction of a landfill does not create a landfill asset retirement obligation. Rather, the asset retirement obligation for cell closure (the cost associated with capping each cell) is incurred in relatively small increments as waste is placed in the landfill. Therefore, the cost required to construct the cell cap is capitalized as an asset retirement cost and a liability of an equal amount is established, based on the discounted cash flow associated with each capping event, as airspace is consumed. Spending for cell capping is reflected as environmental expenditures within operating activities in the statement of cash flows.

Landfill final closure and post-closure liabilities—The balance of landfill final closure and post-closure liabilities at December 31, 2018 and 2017 was $37.8 million and $32.4 million, respectively. The Company has material financial commitments for the costs associated with requirements of the Environmental Protection Agency ("EPA") and the comparable regulatory agency in Canada for landfill final closure and post-closure activities. In the United States, the landfill final closure

(2) SIGNIFICANT ACCOUNTING POLICIES (Continued)

and post-closure requirements are established under the standards of the EPA, and are implemented and applied on a state-by-state basis. The Company develops estimates for the cost of these activities based on an evaluation of site-specific facts and circumstances, including the Company's interpretation of current regulatory requirements and proposed regulatory changes. Such estimates may change in the future due to various circumstances including, but not limited to, permit modifications, changes in legislation or regulations, technological changes and results of environmental studies.

Final closure costs are the costs incurred after the site ceases to accept waste, but before the landfill is certified as closed by the applicable state regulatory agency. These costs generally include the costs required to cap the final cell of the landfill (if not included in cell closure), the costs required to dismantle certain structures for landfills and other landfill improvements, and regulation-mandated groundwater monitoring, and leachate management. Post-closure costs involve the maintenance and monitoring of a landfill site that has been certified closed by the applicable regulatory agency. These costs generally include groundwater monitoring and leachate management. Regulatory post-closure periods are generally 30 years after landfill closure. Final closure and post-closure obligations are accrued on a units-of-consumption basis, such that the present value of the final closure and post-closure obligations are fully accrued at the date the landfill discontinues accepting waste.

Cell closure, final closure and post-closure costs (also referred to as "asset retirement obligations") are calculated by estimating the total obligation in current dollars, adjusted for inflation (1.02% during 2018 and 2017) and discounted at the Company's credit-adjusted risk-free interest rate (5.66% and 6.32% during 2018 and 2017, respectively.)

Non-Landfill Closure and Post-Closure Liabilities

Non-landfill closure costs include costs required to dismantle and decontaminate certain structures and other costs incurred during the closure process. Post-closure costs, if required, include associated maintenance and monitoring costs as required by the closure permit. Post-closure periods are performance-based and are not generally specified in terms of years in the closure permit, but generally range from 10 to 30 years or more.

The Company records its non-landfill closure and post-closure liability by: (i) estimating the current cost of closing a non-landfill facility and the post-closure care of that facility, if required, based upon the closure plan that the Company is required to follow under its operating permit, or in the event the facility operates with a permit that does not contain a closure plan, based upon legally enforceable closure commitments made by the Company to various governmental agencies; (ii) using probability scenarios as to when in the future operations may cease; (iii) inflating the current cost of closing the non-landfill facility on a probability weighted basis using the inflation rate to the time of closing under each probability scenario; and (iv) discounting the future value of each closing scenario back to the present using the credit-adjusted risk-free interest rate. Non-landfill closure and post-closure obligations arise when the Company commences non-landfill facility operations. The carrying value of non-landfill closure and post-closure liabilities at December 31, 2018 and 2017 was $32.1 million and $28.6 million, respectively.

The estimates for non-landfill closure and post-closure liabilities are inherently uncertain due to the possibility that permit and regulatory requirements will change in the future, impacting the estimation of total costs and the timing of the expenditures. Management reviews non-landfill closure and post-closure liabilities for changes to key assumptions that would impact the amount of the recorded liabilities. Changes that would prompt management to revise a liability estimate include changes in legal requirements that impact the Company's expected closure plan or scope of work, in the market price of a significant cost item, in the probability scenarios as to when future operations at a location might cease, or in the expected timing of the cost. Changes in estimates for non-landfill closure and post-closure events immediately impact the required liability and the value of the corresponding asset. If a change is made to a fully-consumed asset, the adjustment is charged immediately to expense. When a change in estimate relates to an asset that has not been fully consumed, the adjustment to the asset recognized in income prospectively as a component of amortization. Historically, material changes to non-landfill closure and post-closure estimates have been infrequent.

Remedial Liabilities

The balance of remedial liabilities at December 31, 2018 and 2017 was $121.0 million and $124.5 million, respectively. Remedial liabilities, including Superfund liabilities, include the costs of removal or containment of contaminated material, treatment of potentially contaminated groundwater and maintenance and monitoring costs necessary to comply with regulatory requirements. Most of the Company's remedial liabilities relate to the active and inactive hazardous waste treatment and disposal facilities which the Company acquired in the last 16 years and Superfund sites owned by third parties for which the Company, or the prior owners of certain of the Company's facilities for which the Company may have certain indemnification

(2) SIGNIFICANT ACCOUNTING POLICIES (Continued)

obligations, have been identified as potentially responsible parties ("PRPs") or potential PRPs. The Company's estimate of remedial liabilities involved an analysis of such factors as: (i) the nature and extent of environmental contamination (if any); (ii) the terms of applicable permits and agreements with regulatory authorities as to cleanup procedures and whether modifications to such permits and agreements will likely need to be negotiated; (iii) the cost of performing anticipated cleanup activities based upon current technology; and (iv) in the case of Superfund and other sites where other parties will also be responsible for a portion of the cleanup costs, the likely allocation of such costs and the ability of such other parties to pay their share. The measurement of remedial liabilities is reviewed at least quarterly and changes in estimates are recognized when identified.

The Company periodically evaluates potential remedial liabilities at sites that it owns or operates or to which the Company or the sellers of the CSD assets (or the respective predecessors of the Company or such sellers) transported or disposed of waste, including 128 Superfund sites as of December 31, 2018. The Company periodically reviews and evaluates sites requiring remediation, including Superfund sites, giving consideration to the nature (i.e., owner, operator, arranger, transporter or generator) and the extent (i.e., amount and nature of waste hauled to the location, number of years of site operations or other relevant factors) of the Company's (or such sellers') alleged connection with the site, the extent (if any) to which the Company believes it may have an obligation to indemnify cleanup costs in connection with the site, the regulatory context surrounding the site, the accuracy and strength of evidence connecting the Company (or such sellers) to the location, the number, connection and financial ability of other named and unnamed potentially responsible parties ("PRPs") and the nature and estimated cost of the likely remedy. Where the Company concludes that it is probable that a liability has been incurred and an amount can be estimated, a provision is made, based upon management's judgment and prior experience, of such estimated liability.

Remedial liabilities are inherently difficult to estimate. Estimating remedial liabilities requires that the existing environmental contamination be understood. There are risks that the actual quantities of contaminants differ from the results of the site investigation, and that contaminants exist that have not been identified by the site investigation. In addition, the amount of remedial liabilities recorded is dependent on the remedial method selected. There is a risk that funds will be expended on a remedial solution that is not successful, which could result in the additional incremental costs of an alternative solution. Such estimates, which are subject to change, are subsequently revised if and when additional or new information becomes available.

Remedial liabilities are discounted only when the timing of the payments is determinable and the amounts are estimable. Management's experience has been that the timing of payments for remedial liabilities is not usually estimable, and therefore the amounts of remedial liabilities are not generally discounted. In the case of remedial liabilities assumed in connection with acquisitions, acquired liabilities are recorded at fair value as of the dates of the acquisitions calculated by inflating costs in current dollars using an estimate of future inflation rates as of the respective acquisition dates until the expected time of payment, and then discounting the amount of the payments to their present value using a risk-free discount rate as of the acquisition dates. Discounts have been and will be applied to the remedial liabilities as follows:


•	Remedial liabilities assumed relating to acquisitions are and will continue to be inflated using the inflation rates at the time of each acquisition (ranging from 1.01% to 2.57%) until the expected time of payment, then discounted at the risk-free interest rate at the time of such acquisition (ranging from 1.37% to 5.99%).


•	Remedial liabilities incurred subsequent to the acquisitions and remedial liabilities of the Company that existed prior to the acquisitions have been and will continue to be recorded at the estimated current value of the liabilities, which is usually neither increased for inflation nor reduced for discounting.

Foreign Currency

The Company has operations in Canada. The functional currencies of those operations are their local currency and therefore assets and liabilities of those foreign operations are translated to U.S. dollars at the exchange rate in effect at the balance sheet date and revenue and expenses at the average exchange rate for the period. Gains and losses from the translation of the consolidated financial statements of foreign subsidiaries into U.S. dollars are included in stockholders' equity as a component of accumulated other comprehensive loss. Gains and losses resulting from foreign currency transactions are recognized in the consolidated statements of operations. Recorded balances that are denominated in a currency other than the functional currency are remeasured to the functional currency using the exchange rate at the balance sheet date and gains or losses are recorded in the statements of operations.

(2) SIGNIFICANT ACCOUNTING POLICIES (Continued)

Advertising Expense

Advertising costs are expensed as incurred. Advertising expense was approximately $10.5 million in 2018, $11.8 million in 2017 and $10.8 million in 2016.

Stock-Based Compensation

Stock-based compensation cost is measured at the grant date based on the fair value of the award and is recognized as expense over the requisite service period, which generally represents the vesting period. In addition, the Company issues awards with performance targets which are recognized as expense over the requisite service period when management believes it is probable those targets will be achieved. The fair value of the Company's grants of restricted stock are based on the quoted market price for the Company's common stock on the respective dates of grant. Forfeitures are recognized as they occur.

Income Taxes

Current income tax expense approximates cash to be paid or refunded for taxes for the applicable period. Deferred tax expense or benefit is the result of changes between deferred tax assets and liabilities. Deferred tax assets and liabilities are determined based upon the temporary differences between the financial statement basis and tax basis of assets and liabilities as well as from net operating loss and tax credit carryforwards as measured by the enacted tax rates, which will be in effect when these differences reverse. The effect of a change in tax rates on deferred tax assets and liabilities is generally recognized in income in the period that includes the enactment date. The Company evaluates the recoverability of future tax deductions and credits and a valuation allowance is established by tax jurisdiction when, based on an evaluation of both positive and negative objective verifiable evidence, it is more likely than not that some portion or all of deferred tax assets will not be realized.

The Company recognizes and measures a tax benefit from uncertain tax positions when it is more likely than not that the tax position will be sustained on examination by the taxing authorities, based on the technical merits of the position. The Company recognizes a liability for unrecognized tax benefits resulting from uncertain tax positions taken or expected to be taken in a tax return. The Company adjusts these liabilities when its judgment changes as a result of the evaluation of new information not previously available. Due to the complexity of some of these uncertainties, the ultimate resolution may result in a payment that is materially different from the current estimate or future recognition of an unrecognized benefit. These differences will be reflected as increases or decreases to income tax expense in the period in which they are determined.

The Company recognizes interest and penalties related to unrecognized tax benefits within the income tax expense line in the consolidated statements of operations. Accrued interest and penalties are included within deferred taxes, unrecognized tax benefits and other long-term liabilities line in the consolidated balance sheet.

Earnings per Share ("EPS")

Basic EPS is calculated by dividing net income by the weighted average number of common shares outstanding during the period. Diluted EPS gives effect to all potentially dilutive common shares that were outstanding during the period.

Recent Accounting Pronouncements

Standards implemented

In May 2014, the Financial Accounting Standards Board ("FASB") issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606), which replaces numerous requirements in U.S. GAAP, including industry-specific requirements, and provides companies with a single revenue recognition model for recognizing revenue from contracts with customers.

On January 1, 2018, the Company adopted Topic 606 using the modified retrospective method for all contracts. Results for reporting periods beginning on the date of adoption are presented under ASC 606, while prior period amounts have not been adjusted and continue to be reported in accordance with the Company's historical accounting methodology pursuant to ASC 605, Revenue Recognition. The only significant impact from the adoption of this standard relates to incremental disclosures now required. Upon adoption, a cumulative effect adjustment was not recorded.

In January 2016, FASB issued ASU 2016-01, Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities. The amendment requires equity investments (except those accounted for under the equity method of accounting, or those that result in consolidation of the investee) to be measured at fair value with changes in fair value recognized in net income. The Company adopted the amendment in the fourth quarter of 2018,

(2) SIGNIFICANT ACCOUNTING POLICIES (Continued)

which resulted in a $1.4 million charge to other (expense) income, net for the change in fair value of equity securities purchased in 2018.

In October 2016, the FASB issued ASU 2016-16, Income Tax - Intra-Entity Transfers of Assets Other than Inventory. The amendment improves the accounting for the income tax consequences of intra-entity transfers of assets other than inventory. The Company adopted this standard on a modified retrospective basis effective January 1, 2018. As a result of adoption, the Company recorded a cumulative effect adjustment that reduced retained earnings by $1.6 million. The impact on the annual provision for income taxes was not material.

In August 2017, the FASB issued ASU 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities. The amendment better aligns an entity’s risk management activities and financial reporting for hedging relationships through changes to both the designation and measurement guidance for qualifying hedging relationships and the presentation of hedge results. The Company adopted the amendment in the third quarter of 2018. Adoption did not have a material impact on the Company's consolidated financial statements.

Standards to be implemented

The Company is evaluating the impact that the below standards to be implemented will have on the Company's consolidated financial statements.

In February 2016, FASB issued ASU 2016-02, Leases (Topic 842). The amendment increases transparency and comparability among organizations by recognizing lease assets and lease liabilities on the balance sheet and disclosing key information about leasing arrangements. The Company is currently finalizing the accounting and internal controls relative to this new pronouncement and will adopt Topic 842 and related amendments on January 1, 2019 using the modified retrospective method of adoption. The Company expects to elect most of the available practical expedients, including the package of practical expedients, which permits entities not to reassess under the new standard their prior conclusions about lease identification, lease classification and initial direct costs. In preparation for adoption of the standard, the Company has implemented internal controls and key system functionality to enable the preparation of financial information. The Company has concluded that the adoption of this standard will have a material impact on the Company’s consolidated balance sheets related to the recognition of right-of-use assets and lease liabilities, but is not expected to have a material impact on the consolidated statements of operations or cash flows. On adoption, the Company currently expects to recognize additional right-of-use assets and lease obligations in the range of $180.0 million to $220.0 million.

BUSINESS COMBINATIONS

12 Months Ended

Dec. 31, 2018

Business Combinations [Abstract]

BUSINESS COMBINATIONS

2018 Acquisitions

On August 31, 2018, the Company acquired a privately-owned company which expands the environmental services and waste oil capabilities of the Company for a $27.3 million purchase price, net of cash. The acquired company is included in the Safety-Kleen and Environmental Services segments. In connection with this acquisition, a preliminary goodwill amount of $15.8 million was recognized. The results of operations of this acquired business were not material in 2018.

On February 23, 2018, the Company completed the acquisition of the U.S. Industrial Cleaning Business of Veolia Environmental Services North America LLC (the "Veolia Business"). The acquisition provides significant scale and industrial services capabilities while increasing the size of the Company's existing U.S. Industrial Services business. The Company acquired the Veolia Business for a preliminary purchase price of $124.0 million, which remains subject to certain post-closing adjustments. The amount of revenue from the Veolia Business included in the Company's results of operations for the year ended December 31, 2018 was $154.0 million. The amount of pre-tax loss from the Veolia Business included in the Company's results of operations for the year ended December 31, 2018 was $0.9 million, which included $14.6 million in depreciation expense as well as $0.6 million of amortization expense related to intangible assets. During the year ended December 31, 2018, the Company incurred acquisition-related costs of approximately $1.4 million in connection with the transaction which

(4) BUSINESS COMBINATIONS (Continued)

are included in selling, general and administrative expenses in the consolidated statements of operations. The Veolia Business is included in the Environmental Services segment.

The components and preliminary allocation of the purchase price for the Veolia Business consist of the following amounts (in thousands):



	At Acquisition Date As Reported December 31, 2018
Accounts receivable, including unbilled receivable	$	38,201
Inventories and supplies	1,126
Prepaid expenses and other current assets	828
Property, plant and equipment	72,243
Permits and other intangibles	5,140
Current liabilities	(18,025		)
Closure and post-closure liabilities	(354		)
Total identifiable net assets	99,159
Goodwill	24,873
Total purchase price	$	124,032

The weighted average amortization period for the intangibles acquired is 8.2 years. The excess of the total purchase price, which includes the aggregate cash consideration paid in excess of the fair value of the tangible net assets and intangible assets acquired, was recorded as goodwill. The goodwill recognized is attributable to the expected operating synergies and growth potential that the Company expects to realize from this acquisition. Goodwill generated from the acquisition is deductible for tax purposes.

Pro forma revenue and earnings amounts on a combined basis as if these acquisitions had been completed on January 1, 2017 are immaterial to the consolidated financial statements of the Company since that date.

2017 Acquisitions

On July 14, 2017, the Company acquired Lonestar West Inc. ("Lonestar"), a public company headquartered in Alberta, Canada, for approximately CAD $41.8 million, ($33.1 million USD), net of cash acquired, which included an equity payout of CAD $0.72 per share to Lonestar shareholders and the assumption of approximately CAD $21.3 million ($16.8 million USD) in outstanding debt, which Clean Harbors subsequently repaid. The acquisition supports the Company's growth in the daylighting and hydro excavation services markets. In addition to increasing the size of the Company's hydro vac fleet, Lonestar's network of locations provides the Company with direct access to key geographic markets in both the United States and Canada. The acquired company is included in the Environmental Services segment. In connection with this acquisition a goodwill amount of $2.8 million was recognized.

On January 31, 2017, the Company acquired a privately held company for a purchase price of approximately $11.9 million in cash, net of cash acquired. The acquired business produces and distributes oil products and therefore complements the Company's closed loop model as it relates to the sale of its oil products. The acquired company is included in the Safety-Kleen segment. In connection with this acquisition a goodwill amount of $5.0 million was recognized.

The combined amount of direct revenue from the acquisitions included in the Company's results of operations for the year ended December 31, 2017 was approximately $14.5 million. Pro forma revenue and earnings amounts on a combined basis as if these acquisitions had been completed on January 1, 2016 are immaterial to the consolidated financial statements of the Company since that date.

(4) BUSINESS COMBINATIONS (Continued)

2016 Acquisitions

During 2016, the Company acquired seven businesses that complement the strategy to create a closed loop model as it relates to the sale of the Company's oil products. These acquisitions provided the Company with three additional oil re-refineries while also expanding its used motor oil collection network and providing greater blending and packaging capabilities. These acquisitions also provide the Company with greater access to customers in the West Coast region of the United States and additional locations with Part B permits. Operations of these acquisitions were primarily integrated into the Safety-Kleen operating segment with certain operations also integrated into the Environmental Services segment.

The combined purchase price for the seven acquisitions was $204.8 million paid in cash and subject to customary post-closing adjustments. The combined amount of direct revenue from the acquisitions included in the Company's results of operations for the year ended December 31, 2016 was approximately $69.8 million. Upon acquisition, the acquired entities were immediately integrated into the Company's operating segments. Therefore it is impracticable to measure earnings attributable to the acquired businesses. During the year ended December 31, 2016, the Company incurred acquisition-related costs of approximately $1.7 million in connection with the transactions which are included in selling, general and administrative expenses in the consolidated statements of operations.

The allocation of the purchase price was based on estimates of the fair value of assets acquired and liabilities assumed as of the acquisition dates. The Company believes that such information provides a reasonable basis for estimating the fair values of assets acquired and liabilities assumed. The Company finalized the purchase accounting for the seven acquisitions in the second quarter of 2017.

The allocation of the purchase price consists of the following amounts (in thousands):



	Final Allocation
Accounts receivable	$	16,242
Inventories and supplies	12,688
Prepaid expenses and other current assets	752
Property, plant and equipment	143,916
Permits and other intangibles	28,856
Current liabilities	(19,905		)
Closure and post-closure liabilities, less current portion	(3,004		)
Remedial liabilities, less current portion	(2,545		)
Deferred taxes, unrecognized tax benefits and other long-term liabilities	(20,219		)
Total identifiable net assets	156,781
Goodwill	47,977
Total purchase price, net of cash acquired	$	204,758

The excess of the total purchase price, which includes the aggregate cash consideration paid in excess of the fair value of the tangible net assets and intangible assets acquired, was recorded as goodwill. The goodwill recognized is attributable to the expected operating synergies and growth potential that the Company expects to realize from these acquisitions. Goodwill generated from the acquisitions was not deductible for tax purposes.

REVENUES

12 Months Ended

Dec. 31, 2018

Revenue from Contract with Customer [Abstract]

REVENUES

Revenue Recognition

The Company generates services and product revenues through the following operating segments: Environmental Services and Safety-Kleen. The Company recognizes revenue when control of the promised goods or services is transferred to the Company's customers, in an amount that reflects the consideration the Company expects to be entitled to in exchange for those goods or services. Product revenues are recognized when the products are delivered and control transfers to the customer.

Nature of Goods and Services

The majority of the Company’s contracts are for services, which are recognized based on time and materials incurred at contractually agreed-upon rates. The Company’s payment terms vary by the type and location of its customers and the products or services offered. The periods between invoicing and when payments are due are not significant. For all periods presented, any amounts billed to customers related to shipping and handling are classified as revenue and the Company's shipping and handling costs are included in costs of revenues. In the course of the Company's operations, it collects sales tax and other excise taxes from its customers and recognizes a current liability which is then relieved when the taxes are remitted to the appropriate governmental authorities. The Company excludes sales and other excise taxes that it collects from customers from its revenues.

(3) REVENUES (Continued)

Disaggregation of Revenue

The following table presents the Company’s third party revenues disaggregated by revenue source (in thousands):



	For the Year Ended December 31, 2018
	Environmental Services		Safety-Kleen		Corporate		Total
Primary Geographical Markets
United States	$	1,598,402	$	1,196,661	$	1,082	$	2,796,145
Canada	405,441		98,694		23		504,158
Total third party revenues	$	2,003,843	$	1,295,355	$	1,105	$	3,300,303

Sources of Revenue (1)
Technical Services	$	1,037,388	$	—	$	—	$	1,037,388
Field and Emergency Response Services	304,727		—		—		304,727
Industrial Services	541,895		—		—		541,895
Oil, Gas and Lodging Services and Other	119,833		—		1,105		120,938
Safety-Kleen Environmental Services	—		795,077		—		795,077
Kleen Performance Products	—		500,278		—		500,278
Total third party revenues	$	2,003,843	$	1,295,355	$	1,105	$	3,300,303

_____________________


1.	All revenue except oil and oil product sales within Kleen Performance Products and product sales within Safety-Kleen Environmental Services, which include various automotive related fluids, shop supplies and direct blended oil sales, are recognized over time. Kleen Performance Products and Safety-Kleen Environmental Services product sales are recognized at a point in time.

Technical Services. Technical Services revenues are generated from fees charged for waste material management and disposal services including onsite environmental management services, collection and transportation, packaging, recycling, treatment and disposal of waste. Revenue is primarily generated by short-term projects, most of which are governed by master service agreements that are long-term in nature. These master service agreements are typically entered into with the Company's larger customers and outline the pricing and legal frameworks for such arrangements. Services are provided based on purchase orders or agreements with the customer and include prices based upon units of volume of waste, and transportation and other fees. Collection and transportation revenues are recognized over time, as the customer receives and consumes the benefits of the services as they are being performed and the Company has a right to payment for performance completed to date. The Company uses the input method to recognize revenue over time, based on time and materials incurred. Revenues for treatment and disposal of waste are recognized upon completion of treatment, final disposition in a landfill or incineration, or when the waste is shipped to a third party for processing and disposal. The Company periodically enters into bundled arrangements for the collection and transportation and disposal of waste. For such arrangements, transportation and disposal are considered distinct performance obligations and the Company allocates revenue to each based on their relative standalone selling price (i.e. the estimated price that a customer would pay for the services on a standalone basis). Revenues from waste that is not yet completely processed and disposed and the related costs are deferred. The revenue is recognized and the deferred costs are expensed when the related services are completed. The period between collection and transportation and the final processing and disposal ranges depending on location of the customer, but generally is measured in days.

Field and Emergency Response Services. Field Services revenues are generated from cleanup services at customer sites, including municipalities and utilities, or other locations on a scheduled or emergency response basis. Services include confined space entry for tank cleaning, site decontamination, large remediation projects, demolition, spill cleanup on land and water, railcar cleaning, product recovery and transfer and vacuum services. Additional services include filtration and water treatment services. Response services for environmental emergencies include any scale from man-made disasters such as oil spills, to natural disasters such as hurricanes. These services are provided based on purchase orders or agreements with customers and include prices generally based upon daily, hourly or job rates for equipment, materials and personnel. The Company recognizes revenue for these services over time, as the customer receives and consumes the benefits of the service as they are being performed and the Company has a right to payment for performance completed to date. The Company uses the input method to

(3) REVENUES (Continued)

recognize revenue over time, based on time and materials incurred. The duration of such services can be over a number of hours, several days or even months for larger scale projects.

Industrial Services. Industrial Services revenues are generated from industrial and specialty services provided to refineries, mines, upgraders, chemical plants, pulp and paper mills, manufacturing facilities, power generation facilities and other industrial customers throughout North America. Services include in-plant cleaning and maintenance services, plant outage and turnaround services, decoking and pigging, chemical cleaning, high and ultra-high pressure water cleaning, pipeline inspection and coating services, large tank and surface impoundment cleaning, oilfield transport, daylighting, production services and directional boring services (previously included in Oil, Gas and Lodging service offerings) supporting drilling, completions and production programs. These services are provided based on purchase orders or agreements with the customer and include prices based upon daily, hourly or job rates for equipment, materials and personnel. The Company recognizes revenue for these services over time, as the customer receives and consumes the benefits of the services as they are being performed and the Company has a right to payment for performance completed to date. The Company uses the input method to recognize revenue over time, based on time and materials incurred.

Oil, Gas and Lodging Services and Other. Oil, Gas and Lodging Services and Other is primarily comprised of revenues generated from providing Oil and Gas Field Services that support upstream activities such as exploration and drilling for oil and gas companies and Lodging Services to customers in Western Canada. The Company recognizes Oil and Gas Field Services revenue over time, as the customer receives and consumes the benefits of the services as they are being performed and the Company has a right to payment for performance completed to date. The Company uses the input method to recognize revenue over time, based on time and materials incurred. Revenue for lodging accommodation services is recognized over time based on passage of time.

Safety-Kleen Environmental Services. Safety-Kleen Environmental Services revenues are generated from providing parts washer services, containerized waste handling and disposal services, oil collection services, direct sales of blended oil products, and other complementary services and product sales. Containerized waste services consist of profiling, collecting, transporting and recycling or disposing of a wide variety of waste. Other products and services include vacuum services, sale of complementary supply products including automotive fluids and shop supplies and other environmental services. Revenues from parts washer services include fees charged to customers for their use of parts washer equipment, to clean and maintain parts washer equipment and to remove and replace used cleaning fluids. Parts washer services are considered a single performance obligation due to the highly integrated and interdependent nature of the arrangement. Revenue from parts washer services is recognized over the service interval as the customer receives the benefit of the services. Collection and transportation revenues are recognized over time, as the customer receives and consumes the benefits of the services as they are being performed and the Company has a right to payment for performance completed to date. The Company uses the input method to recognize revenue over time, based on time and materials incurred. Product revenue is recognized upon the transfer of control whereby control transfers when the products are delivered to the customer.

Kleen Performance Products. Kleen Performance Products revenues are generated from sales of high quality base and blended lubricating oils to third-party distributors, government agencies, fleets, railroads and industrial customers. The business also sells recycled fuel oil to asphalt plants, industrial plants, blenders, pulp and paper companies, vacuum gas oil producers and marine diesel oil producers. Revenue for oil products is recognized at a point in time, upon the transfer of control. Control transfers when the products are delivered to the customer.

Contract Balances



	December 31, 2018		December 31, 2017
Receivables	$	606,952	$	528,924
Contract Assets (Unbilled Receivables)	54,794		35,922
Contract Liabilities (Deferred Revenue)	61,843		67,822

The timing of revenue recognition, billings and cash collections results in billed accounts receivable, unbilled receivables (contract assets), and customer advances and deposits or deferred revenue (contract liabilities) on the Consolidated Balance Sheet. Generally, billing occurs subsequent to revenue recognition, as a right to payment is not just subject to passage of time, resulting in contract assets. Contract assets are generally classified as current. The Company sometimes receives advances or deposits from its customers before revenue is recognized, resulting in contract liabilities. These assets and liabilities are

(3) REVENUES (Continued)

reported on the Consolidated Balance Sheet on a contract-by-contract basis at the end of each reporting period. As part of the acquisition of the Veolia Business (as defined in Note 4, "Business Combinations") on February 23, 2018, the Company acquired receivables and contract assets of $20.8 million and $17.4 million, respectively. Changes in the contract asset and liability balances during the years ended December 31, 2018 and December 31, 2017 were not materially impacted by any other

factors. The contract liability balances at the beginning of each period presented were generally fully recognized in the subsequent three-month period.

Variable Consideration

The nature of the Company's contracts give rise to certain types of variable consideration, including in limited cases volume discounts. Accordingly, management establishes a revenue allowance to cover the estimated amounts of revenue that may need to be credited to customers' accounts in future periods. The Company estimates the amount of variable consideration to include in the estimated transaction price based on historical experience, anticipated performance and its best judgment at the time and to the extent it is probable that a significant reversal of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is resolved.

Contract Costs

Contract costs include direct and incremental costs to obtain or fulfill a contract. The Company’s contract costs that are subject to capitalization are comprised of costs associated with parts washer services and costs associated with the treatment and disposal of waste. Parts washer costs include costs of solvent, commissions paid relating to revenue generated from parts washer services, and transportation costs associated with transferring the product picked up from the services as it is returned to the Company’s facilities or a third party site. Costs related to the treatment of waste include costs for waste receiving, drum movement and storage, waste consolidation and transportation between facilities. Deferred costs associated with parts washer services are amortized ratably over the average service interval, which ranges between seven and 14 weeks. Deferred costs related to treatment and disposal of waste are recognized when the corresponding waste is disposed of and are included in deferred costs within total current assets in the Company’s consolidated balance sheets. The deferred contract cost balances at the beginning of each period presented were fully recognized in cost of revenue in the subsequent three-month period.

Prior Accounting

Prior to January 1, 2018 and the adoption of ASC 606, the Company recognized revenue when persuasive evidence of an arrangement existed, delivery had occurred or services had been rendered, the price was fixed or determinable, and collection was reasonably assured. Management established a revenue allowance to cover the estimated amounts of revenue that may need to be credited to customers' accounts in future periods due to discounts, billing disputes and other adjustments. The Company recorded a provision for revenue allowances based on specific review of particular customers, historical trends and other relevant information.

DISPOSITION OF BUSINESS

12 Months Ended

Dec. 31, 2018

Discontinued Operations and Disposal Groups [Abstract]

DISPOSITION OF BUSINESS

DISPOSITION OF BUSINESSES

2017 Disposition

On June 30, 2017, the Company completed the sale of its Transformer Services business, as part of its continuous focus on improving or divesting certain non-core operations. The Transformer Services business was a non-core business previously included within the former Technical Services operating segment and was sold for $45.5 million ($43.4 million net of $2.1 million in transactional related costs). As a result of the sale, the Company recognized during the year ended December 31,

(5) DISPOSITION OF BUSINESSES (Continued)

2017, a pre-tax gain of $30.7 million which was included in gain on sale of business in the Company’s consolidated statement of operations.

The following table presents the carrying amounts of the Company's Transformer Services business that was disposed of on June 30, 2017 (in thousands):



	June 30, 2017
Total current assets	$	7,241
Property, plant and equipment, net	8,773
Total other assets	1,681
Total assets divested	17,695
Total current liabilities	3,849
Total other liabilities	1,170
Total liabilities divested	5,019
Net carrying value divested	$	12,676

The Company evaluated the disposition and determined it did not meet the “major effect” criteria for classification as a discontinued operation largely due to the nature and size of the operations of the disposed entity. However, the Company determined that the disposition represented an individually significant component of the Company’s business. The following table presents income attributable to the Transformer Services business included in the Company's consolidated results of operations for each of the periods shown and through its disposition on June 30, 2017 (in thousands):



	For the years ended December 31,
	2017		2016
Income before provision (benefit) for income taxes	$	2,771	$	4,187

2016 Disposition

On September 1, 2016, the Company completed the sale of its Catalyst Services business, which was a non-core business previously included within the former Industrial Services operating segment, for approximately $50.6 million ($49.2 million net of cash retained by the Catalyst Services business). As a result of the sale, the Company recognized during the year ended December 31, 2016, a pre-tax gain of $16.9 million which was included in gain on sale of business in the Company’s consolidated statement of operations. Inclusive within this gain was $1.6 million of transactional related costs. During the first quarter of 2017, the Company and the buyer of the Catalyst Services business agreed to final working capital amounts and as a result the Company received $2.0 million of final sale proceeds.

(5) DISPOSITION OF BUSINESSES (Continued)

The following table presents the carrying amounts of the Company's Catalyst Services business immediately preceding the disposition on September 1, 2016 (in thousands):



	September 1, 2016
Total current assets	$	19,019
Property, plant and equipment, net	11,154
Total other assets	6,500
Total assets divested	36,673
Total current liabilities	4,040
Total other liabilities	566
Total liabilities divested	4,606
Net carrying value divested	$	32,067

The Company evaluated the disposition and determined it did not meet the “major effect” criteria for classification as a discontinued operation largely due to the nature and size of the operations of the disposed of entity. However, the Company determined that the disposition did represent an individually significant component of its business. The following table presents income attributable to the Catalyst Services business included in the Company's consolidated results of operations for the period shown and through its disposition on September 1, 2016 (in thousands):



	For the year ended December 31,
	2016
Income before provision (benefit) for income taxes	$	290

PROPERTY, PLANT, AND EQUIPMENT

12 Months Ended

Dec. 31, 2018

Property, Plant and Equipment [Abstract]

PROPERTY, PLANT, AND EQUIPMENT

PROPERTY, PLANT AND EQUIPMENT

Property, plant and equipment consisted of the following (in thousands):



	December 31, 2018		December 31, 2017
Land	$	123,734	$	121,658
Asset retirement costs (non-landfill)	15,148		14,593
Landfill assets	154,918		144,539
Buildings and improvements	440,188		414,384
Camp and lodging equipment	152,998		170,012
Vehicles	721,735		617,959
Equipment	1,697,490		1,644,102
Furniture and fixtures	5,453		5,708
Construction in progress	20,931		57,618
	3,332,595		3,190,573
Less - accumulated depreciation and amortization	1,770,617		1,603,208
Total property, plant and equipment, net	$	1,561,978	$	1,587,365

Interest in the amount of $0.6 million, $0.6 million and $5.5 million was capitalized to property, plant and equipment during the years ended December 31, 2018, 2017 and 2016, respectively. Depreciation expense, inclusive of landfill amortization was $264.3 million, $251.4 million and $247.0 million for the years ended December 31, 2018, 2017 and 2016, respectively.

GOODWILL AND OTHER INTANGIBLE ASSETS

12 Months Ended

Dec. 31, 2018

Goodwill and Intangible Assets Disclosure [Abstract]

GOODWILL AND OTHER INTANGIBLE ASSETS

The changes in goodwill for the years ended December 31, 2018 and 2017 were as follows (in thousands):



	Environmental Services			Safety-Kleen			Totals
Balance at January 1, 2017	$	169,084		$	296,070		$	465,154
Increase from current period acquisitions	3,000			5,687			8,687
Measurement period adjustments from prior period acquisitions	—			2,186			2,186
Decrease from disposition of business	(1,300		)	—			(1,300		)
Foreign currency translation	1,602			2,194			3,796
Balance at December 31, 2017	$	172,386		$	306,137		$	478,523
Increase from current period acquisitions	37,007			3,697			40,704
Measurement period adjustments from prior period acquisitions	(78		)	—			(78		)
Foreign currency translation	(2,296		)	(2,664		)	(4,960		)
Balance at December 31, 2018	$	207,019		$	307,170		$	514,189

The Company assesses goodwill for impairment on an annual basis as of December 31, or at an interim date when events or changes in the business environment would more likely than not reduce the fair value of a reporting unit below its carrying value.

The Company conducted its annual impairment test of goodwill as of December 31, 2018 and determined that no adjustment to the carrying value of goodwill for any reporting unit was then necessary because the fair values of the reporting units exceeded their respective carrying values. The fair value of all reporting units was determined using an income approach based upon estimates of future discounted cash flows. The resulting estimates of fair value were validated through the consideration of other factors such as the fair value of comparable companies to the reporting units and a reconciliation of the sum of all estimated fair values of the reporting units to the Company’s overall market capitalization. In all cases, the estimated fair values of the reporting units significantly exceeded their carrying values.

(8) GOODWILL AND OTHER INTANGIBLE ASSETS (Continued)

Significant judgments and unobservable inputs categorized as Level 3 in the fair value hierarchy are inherent in the impairment tests performed and include assumptions about the amount and timing of expected future cash flows, growth rates, and the determination of appropriate discount rates. Level 3 inputs are unobservable inputs for the asset or liability in which there is little, if any, market activity for the asset or liability at the measurement date. The Company believes that the assumptions used in its annual and any interim date impairment tests are reasonable, but variations in any of the assumptions may result in different calculations of fair values.

The impacts of any adverse business and market conditions which impact the overall performance of the Company's reporting units will continue to be monitored. If the Company's reporting units do not achieve the financial performance that the Company expects, it is possible that goodwill impairment charges may result. There can therefore be no assurance that future events will not result in an impairment of goodwill.

At December 31, 2018, the total of accumulated goodwill impairment charges was $189.4 million, of which $34.0 million was recorded during the year ended December 31, 2016 within the Environmental Services reporting unit, due to economic conditions in Western Canada's Oil Sands region and the impacts on the Company's lodging operations.

As of December 31, 2018 and 2017, the Company's finite-lived and indefinite-lived intangible assets consisted of the following (in thousands):



	December 31, 2018						December 31, 2017
	Cost		Accumulated Amortization		Net		Cost		Accumulated Amortization		Net
Permits	$	177,583	$	79,358	$	98,225	$	174,721	$	74,347	$	100,374
Customer and supplier relationships	393,487		179,824		213,663		399,224		158,972		240,252
Other intangible assets	37,262		29,743		7,519		36,766		31,592		5,174
Total amortizable permits and other intangible assets	608,332		288,925		319,407		610,711		264,911		345,800
Trademarks and trade names	122,468		—		122,468		123,328		—		123,328
Total permits and other intangible assets	$	730,800	$	288,925	$	441,875	$	734,039	$	264,911	$	469,128

The Company regularly monitors and assesses whether events or changes in circumstances relative to the Company's business might indicate that future cash flows attributable to the Company's asset groups may not be sufficient to recover the current value of those assets. During the year ended and as of December 31, 2018, there were no events or changes in circumstances which would indicate that the carrying values of the Company's asset groups would not be recoverable and thus no impairment charge was recorded related to the Company's long-lived assets. If expectations of future cash flows were to decrease in the future as a result of worse than expected or prolonged periods of depressed activity, future impairments may become evident.

Amortization expense of permits and other intangible assets for the years ended December 31, 2018, 2017 and 2016 were $34.4 million, $37.0 million and $40.0 million, respectively.

The expected amortization of the net carrying amount of finite-lived intangible assets at December 31, 2018 is as follows (in thousands):



Years Ending December 31,	Expected Amortization
2019	$	33,091
2020	30,195
2021	27,553
2022	27,386
2023	23,468
Thereafter	177,714
	$	319,407

ACCRUED EXPENSES

12 Months Ended

Dec. 31, 2018

Payables and Accruals [Abstract]

ACCRUED EXPENSES

Accrued expenses consisted of the following at December 31 (in thousands):



	December 31, 2018		December 31, 2017
Insurance	$	70,217	$	57,889
Interest	3,930		12,660
Accrued compensation and benefits	77,881		55,861
Income, real estate, sales and other taxes	25,670		27,330
Other	55,707		34,242
	$	233,405	$	187,982

As of December 31, 2018 and 2017, accrued insurance included health insurance costs of $14.7 million and $9.0 million, respectively, and accruals for losses under our workers' compensation, comprehensive general liability and vehicle liability self-insurance programs of $53.9 million and $47.9 million, respectively. The increase in our self-insurance liabilities from the comparable period in 2017 was primarily due to the acquisition of the Veolia Business, for which the Company assumed workers' compensation, general liability and vehicle liability claims reserves.

Accrued compensation and benefits increased by $22.0 million from the comparable period in 2017 due to an increase in variable compensation, which was attributable to greater revenue and earnings achieved in 2018.

As of December 31, 2018 and 2017, other accrued expenses included accrued legal matters of $7.5 million and $1.4 million, respectively, and accrued severance charges of $2.7 million and $3.5 million, respectively. The increase in accrued legal matters was primarily due to the acquisition of the Veolia Business and certain liabilities assumed by the Company. Also included in the December 31, 2018 other accrued expenses balance was an $8.8 million derivative liability, recorded at fair value, related to the Company's cash flow hedges.

CLOSURE AND POST-CLOSURE LIABILITIES

12 Months Ended

Dec. 31, 2018

Asset Retirement Obligation Disclosure [Abstract]

CLOSURE AND POST-CLOSURE LIABILITIES

The changes to closure and post-closure liabilities (also referred to as "asset retirement obligations") from January 1, 2017 through December 31, 2018 were as follows (in thousands):



	Landfill Retirement Liability			Non-Landfill Retirement Liability			Total
Balance at January 1, 2017	$	30,630		$	27,701		$	58,331
Liabilities assumed in acquisitions	—			59			59
Measurement period adjustments from prior period acquisitions	—			596			596
New asset retirement obligations	1,881			—			1,881
Adjustment related to disposition of business	—			(1,170		)	(1,170		)
Accretion	2,243			2,505			4,748
Changes in estimates recorded to statement of operations	(131		)	(109		)	(240		)
Changes in estimates recorded to balance sheet	364			(591		)	(227		)
Expenditures	(2,777		)	(448		)	(3,225		)
Currency translation and other	172			112			284
Balance at December 31, 2017	32,382			28,655			61,037
Liabilities assumed in acquisitions	—			685			685
New asset retirement obligations	2,518			—			2,518
Accretion	2,537			2,567			5,104
Changes in estimates recorded to statement of operations	(37		)	1,497			1,460
Changes in estimates recorded to balance sheet	1,867			64			1,931
Expenditures	(1,224		)	(1,057		)	(2,281		)
Currency translation and other	(234		)	(289		)	(523		)
Balance at December 31, 2018	$	37,809		$	32,122		$	69,931

(10) CLOSURE AND POST-CLOSURE LIABILITIES (Continued)

All of the landfill facilities included in the above table were active as of December 31, 2018 and 2017. The 2018 environmental change in estimate recorded to the statement of operations includes $1.2 million related to increased facility closure costs at one of our locations. There were no significant (benefits) charges in 2017 resulting from changes in estimates for closure and post-closure liabilities.

New asset retirement obligations incurred during 2018 and 2017 were discounted at the credit-adjusted risk-free rate of 5.66% and 6.32%, respectively.

Anticipated payments (based on current estimated costs and anticipated timing of necessary regulatory approvals to commence work on closure and post-closure activities) for each of the next five years and thereafter are as follows (in thousands):



Year ending December 31,
2019	$	10,574
2020	9,424
2021	10,941
2022	7,626
2023	9,264
Thereafter	271,314
Undiscounted closure and post-closure liabilities	319,143
Less: Discount at credit-adjusted risk-free rate	(155,999		)
Less: Undiscounted estimated closure and post-closure liabilities relating to airspace not yet consumed	(93,213		)
Present value of closure and post-closure liabilities	$	69,931

REMEDIAL LIABILITIES

12 Months Ended

Dec. 31, 2018

Environmental Remediation Obligations [Abstract]

REMEDIAL LIABILITIES

The changes to remedial liabilities from January 1, 2017 through December 31, 2018 were as follows (in thousands):



	Remedial Liabilities for Landfill Sites			Remedial Liabilities for Inactive Sites			Remedial Liabilities (Including Superfund) for Non-Landfill Operations			Total
Balance at January 1, 2017	$	1,777		$	64,151		$	62,079		$	128,007
Measurement period adjustments from prior period acquisitions	—			—			504			504
Accretion	86			2,648			1,978			4,712
Changes in estimates recorded to statement of operations	(21		)	(289		)	355			45
Expenditures	(42		)	(3,906		)	(5,792		)	(9,740		)
Currency translation and other	—			2,738			(1,798		)	940
Balance at December 31, 2017	1,800			65,342			57,326			124,468
Accretion	86			2,745			1,871			4,702
Changes in estimates recorded to statement of operations	(1		)	130			558			687
Expenditures	(47		)	(3,759		)	(4,028		)	(7,834		)
Currency translation and other	—			857			(1,863		)	(1,006		)
Balance at December 31, 2018	$	1,838		$	65,315		$	53,864		$	121,017

(11) REMEDIAL LIABILITIES (Continued)

There were no significant (benefits) charges in 2018 and 2017 resulting from changes in estimates for remedial liabilities. Anticipated payments at December 31, 2018 (based on current estimated costs and anticipated timing of necessary regulatory approvals to commence work on remedial activities) for each of the next five years and thereafter were as follows (in thousands):



Year ending December 31,
2019	$	13,975
2020	15,467
2021	14,593
2022	9,560
2023	8,688
Thereafter	81,453
Undiscounted remedial liabilities	143,736
Less: Discount	(22,719		)
Total remedial liabilities	$	121,017

Based on currently available facts and legal interpretations, existing technology, and presently enacted laws and regulations, the Company estimates that its aggregate liabilities as of December 31, 2018 for future remediation relating to all of its owned or leased facilities and the Superfund sites for which the Company has current or potential future liability is approximately $121.0 million. The Company also estimates that it is reasonably possible that the amount of such total liabilities could be as much as $22.8 million more. Future changes in either available technology or applicable laws or regulations could affect such estimates of remedial liabilities. Since the Company's satisfaction of the liabilities will occur over many years, the Company cannot now reasonably predict the nature or extent of future changes in either available technology or applicable laws or regulations and the impact that those changes, if any, might have on the current estimates of remedial liabilities.

The following tables show, respectively, (i) the amounts of such estimated liabilities associated with the types of facilities and sites involved and (ii) the amounts of such estimated liabilities associated with each facility or site which represents at least 5% of the total and with all other facilities and sites as a group and as of December 31, 2018.

Estimates Based on Type of Facility or Site (in thousands):



Type of Facility or Site	Remedial Liability		% of Total		Reasonably Possible Additional Liabilities(1)
Facilities now used in active conduct of the Company's business (41 facilities)	$	48,506	40.1	%	$	11,171
Inactive facilities not now used in active conduct of the Company's business but most of which were acquired because the assumption of remedial liabilities for such facilities was part of the purchase price for the CSD assets (35 facilities)	64,344		53.2		10,782
Superfund sites owned by third parties (17 sites)	8,167		6.7		817
Total	$	121,017	100.0	%	$	22,770

___________________________________


(1)	Amounts represent the high end of the range of management's best estimate of the reasonably possible additional liabilities.

(11) REMEDIAL LIABILITIES (Continued)

Estimates Based on Amount of Potential Liability (in thousands):



Location	Type of Facility or Site	Remedial Liability		% of Total		Reasonably Possible Additional Liabilities(1)
Baton Rouge, LA(2)	Closed incinerator and landfill	$	23,314	19.3	%	$	3,963
Bridgeport, NJ	Closed incinerator	18,616		15.4		2,577
Mercier, Quebec(2)	Idled incinerator and legal proceedings	9,809		8.1		1,037
Linden, NJ	Operating solvent recycling center	7,487		6.2		790
Various(2)	All other incinerators, landfills, wastewater treatment facilities and service centers (72 facilities)	53,624		44.3		13,586
Various(2)	Superfund sites (each representing less than 5% of total liabilities) owned by third parties (17 sites)	8,167		6.7		817
Total		$	121,017	100.0	%	$	22,770

_________________________________


(1)	Amounts represent the high end of the range of management's best estimate of the reasonably possible additional liabilities.


(2)	$17.9 million of the $121.0 million remedial liabilities and $1.8 million of the $22.8 million reasonably possible additional liabilities include estimates of remediation liabilities related to the legal and administrative proceedings discussed in Note 18, "Commitments and Contingencies," as well as other such estimated remedial liabilities.

Revisions to remediation reserve requirements may result in upward or downward adjustments to income from operations in any given period. The Company believes that its extensive experience in the environmental services business, as well as its involvement with a large number of sites, provides a reasonable basis for estimating its aggregate liability. It is possible, however, that technological, regulatory or enforcement developments, the results of environmental studies, or other factors could necessitate the recording of additional liabilities or the revision of currently recorded liabilities that could be material. The impact of such future events cannot be estimated at the current time.

FINANCING ARRANGEMENTS

12 Months Ended

Dec. 31, 2018

Debt Disclosure [Abstract]

FINANCING ARRANGEMENTS

The following table is a summary of the Company's financing arrangements (in thousands):



Current Obligations:	December 31, 2018			December 31, 2017
Senior secured Term Loan Agreement ("Term Loan Agreement")	$	7,535		$	4,000

Long-Term Obligations:
Senior secured Term Loan Agreement due June 30, 2024	$	734,697		$	394,000
Senior unsecured notes, at 5.25%, due August 1, 2020 ("2020 Notes")	—			400,000
Senior unsecured notes, at 5.125%, due June 1, 2021 ("2021 Notes")	845,000			845,000
Long-term obligations, at par	$	1,579,697		$	1,639,000
Unamortized debt issuance costs and premium, net	$	(14,676	)	$	(13,463	)
Long-term obligations, at carrying value	$	1,565,021		$	1,625,537

Financing Activities

Senior Secured Term Loans. On April 17, 2018, the Company, and substantially all of the Company's domestic subsidiaries as guarantors, entered into the first amendment (the “First Amendment”) of the Term Loan Agreement. The First Amendment reduced the applicable interest rate margin for the Company’s initial term loans (the "Term Loans") outstanding under the Term Loan Agreement by 25 basis points for both Eurocurrency borrowings and base rate borrowings. After giving effect to the repricing, the applicable interest rate margins for the Term Loans are 1.75% for Eurocurrency borrowings and 0.75% for base rate borrowings.

(12) FINANCING ARRANGEMENTS (Continued)

On July 19, 2018, the Company, and substantially all of the Company’s domestic subsidiaries as guarantors, entered into an Incremental Facility Amendment (the “Incremental Facility Amendment”) to the Company’s Term Loan Agreement. The Incremental Facility Amendment increased the principal amount of the Term Loans outstanding under the Term Loan Agreement by $350.0 million. Term Loans under the Term Loan Agreement will mature on June 30, 2024 and may be prepaid at any time without premium or penalty other than customary breakage costs with respect to Eurodollar based loans. The Company’s obligations under the Term Loan Agreement are guaranteed by all of the Company’s domestic restricted subsidiaries and secured by liens on substantially all of the assets of the Company and the guarantors. The effective interest rate of the Term Loans on December 31, 2018 was 4.27%.

Concurrently with the closing on July 19, 2018 of the Incremental Facility Amendment, the Company purchased $322.0 million aggregate principal of the 2020 Notes. The total amount paid in purchasing the 2020 Notes was $330.9 million inclusive of $7.9 million of accrued interest and $1.0 million of debt redemption fees. On August 1, 2018, the Company redeemed the remaining $78.0 million of outstanding 2020 Notes.

At December 31, 2018 and December 31, 2017, the fair value of the Term Loan Agreement debt was $707.0 million and $400.5 million, respectively, based on quoted market prices or other available market data. The fair value of the Term Loan Agreement debt is considered a Level 2 measure according to the fair value hierarchy.

Senior Unsecured Notes. In 2012, the Company issued $800.0 million aggregate principal amount of 5.25% senior unsecured notes due August 1, 2020 (the "2020 Notes") with semi-annual fixed interest payments on February 1 and August 1 of each year. The Company repurchased or redeemed $400.0 million principal amount of the 2020 Notes during 2017 and, as described above, the Company repurchased or redeemed the remaining $400.0 million principal amount of the 2020 Notes during 2018. At December 31, 2017, the fair value of the 2020 Notes was $404.6 million based on quoted market prices for the instrument. The fair value of the 2020 Notes was considered a Level 2 measure according to the fair value hierarchy.

In 2012, the Company issued $600.0 million aggregate principal amount of 5.125% senior unsecured notes due June 1, 2021 (the "2021 Notes") with semi-annual fixed interest payments on June 1 and December 1 of each year. The Company repurchased $5.0 million principal amount of 2021 Notes during 2014. On March 14, 2016, the Company issued an additional $250.0 million aggregate principal amount of 2021 Notes as additional notes under the related indenture. At December 31, 2018 and 2017, the fair value of the Company's 2021 Notes was $845.0 million and $855.7 million, respectively, based on quoted market prices or other available market data. The fair value of the 2021 Notes is considered a Level 2 measure according to the fair value hierarchy. Upon proper notice to the holders of the 2021 Notes, the Company may presently redeem some or all of the 2021 Notes at par value plus unpaid interest.

The 2021 Notes and the related indentures contain various customary non-financial covenants and are guaranteed by substantially all of the Company's current and future domestic restricted subsidiaries. The 2021 Notes are the Company's and the guarantors' senior unsecured obligations ranking equally with the Company's and the guarantors' existing and future senior unsecured obligations and senior to any future indebtedness that is expressly subordinated to the 2021 Notes and the guarantees. The 2021 Notes are effectively subordinated to all of the Company's and the Company subsidiaries' secured indebtedness under the Company's Term Loan Agreement, revolving credit facility and capital lease obligations to the extent of the value of the assets securing such secured indebtedness. The 2021 Notes are not guaranteed by the Company's existing and future Canadian or other foreign subsidiaries, and are structurally subordinated to all indebtedness and other liabilities, including trade payables, of the Company's subsidiaries that are not guarantors of the 2021 Notes.

Revolving Credit Facility. On November 1, 2016, the Company and one of the Company's subsidiaries (the "Canadian Borrower") entered into an amended and restated credit agreement for the Company's revolving credit facility with Bank of America, N.A. (“BofA”), as agent for the lenders under the facility (the "Agent"). Under the amended and restated facility, the Company has the right to obtain revolving loans and letters of credit for a combined maximum of up to $300.0 million (with a sub-limit of $250.0 million for letters of credit) and the Canadian Borrower has the right to obtain revolving loans and letters of credit for a combined maximum of up to $100.0 million (with a $75.0 million sub-limit for letters of credit). Availability under the U.S. line is subject to a borrowing base basically comprised of 85% of the eligible accounts receivable of the Company and its U.S. subsidiaries plus 100% of cash deposited in a controlled account with the Agent, and availability under the Canadian line is subject to a borrowing base basically comprised of 85% of the eligible accounts receivable of the Company’s Canadian subsidiaries plus 100% of cash deposited in a controlled account with the Agent’s Canadian affiliate. Subject to certain conditions, the facility will expire on November 1, 2021.

(12) FINANCING ARRANGEMENTS (Continued)

Borrowings under the revolving credit facility bear interest at a rate of, at the Company’s option, either (i) LIBOR plus an applicable margin ranging from 1.25% to 1.50% per annum based primarily on the level of the Company’s average liquidity for the most recent 30 day period or (ii) BofA’s base rate plus an applicable margin ranging from 0.25% to 0.50% per annum based primarily on such average liquidity. There is also an unused line fee, calculated on the then unused portion of the lenders’ $400.0 million maximum commitments, ranging from 0.25% to 0.30% per annum of the unused commitment. For outstanding letters of credit, the Company will pay to the lenders a fee equal to the then applicable LIBOR margin described above, and to the issuing banks a standard fronting fee and customary fees and charges in connection with all amendments, extensions, draws and other actions with respect to letters of credit.

The Company’s obligations under the revolving credit facility (including revolving loans and reimbursement obligations for outstanding letters of credit) are guaranteed by substantially all of the Company’s U.S. subsidiaries and secured by a first lien on the Company’s and its U.S. subsidiaries’ accounts receivable. The Canadian Borrower’s obligations under the facility are guaranteed by substantially all of the Company’s Canadian subsidiaries and secured by a first lien on the accounts receivable of the Canadian subsidiaries.

The Company utilizes letters of credit primarily as security for financial assurance which it has been required to provide to regulatory bodies for its hazardous waste facilities and which would be called only in the event that the Company fails to satisfy closure, post-closure and other obligations under the permits issued by those regulatory bodies for such licensed facilities. On August 1, 2018, the Company borrowed $50.0 million under the revolving credit facility in connection with the redemption of $78.0 million of 2020 Notes. The Company repaid the $50.0 million borrowing during the fourth quarter of 2018. At December 31, 2018 and 2017, the revolving credit facility had no outstanding loan balances, availability of $235.4 million and $217.8 million, respectively, and outstanding letters of credit of $130.1 million and $134.1 million, respectively.

Cash Flow Hedges

The Company’s strategy to hedge against fluctuations in variable interest rates involves entering into interest rate derivative agreements to hedge against adverse movements in interest rates. For interest rate derivatives deemed to be effective cash flow hedges, the change in fair value is recorded in stockholders’ equity as a component of accumulated other comprehensive loss and included in interest expense at the same time as interest expense is affected by the hedged transaction. Differences paid or received over the life of the agreements are recorded as additions to or reductions of interest expense on the underlying debt.

Although the interest rate on all $742.2 million aggregate principal amount of Term Loans which were outstanding on December 31, 2018 is variable under the Term Loan Agreement, the Company has effectively fixed the interest rate on $350.0 million aggregate principal amount of the Term Loans outstanding by entering into interest rate swap agreements in 2018 with a notional amount of $350.0 million. Under the terms of the interest rate swap agreements, the Company receives interest based on the 1-month LIBOR index and pays interest at a weighted average rate of approximately 2.92%. When combined with the 1.75% interest rate margin for Eurocurrency borrowings, the effective annual interest rate on such $350.0 million aggregate principal amount of Term Loans is therefore approximately 4.67%.

The Company recognizes derivative instruments as either assets or liabilities on the balance sheet at fair value. No ineffectiveness has been identified on these swaps and, therefore, all unrealized changes in fair value are recorded in accumulated other comprehensive loss. Amounts are reclassified from accumulated other comprehensive loss into interest expense on the Statement of Operations in the same period or periods during which the hedged transaction affects earnings.

As of December 31, 2018, the Company recorded a derivative liability with a fair value of $8.8 million within accrued expenses in connection with these cash flow hedges.

The fair value of the interest rate swaps included in the Level 2 tier of the fair value hierarchy is calculated using discounted cash flow valuation methodologies based upon the one month LIBOR yield curves that are observable at commonly quoted intervals for the full term of the swaps. Level 2 utilizes quoted market prices in markets that are not active, broker or dealer quotations, or alternative pricing sources with reasonable levels of price transparency for similar assets and liabilities.

INCOME TAXES

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

INCOME TAXES

The domestic and foreign components of income before provision (benefit) for income taxes were as follows (in thousands):



	For the Year Ended December 31,
	2018			2017			2016
Domestic	$	115,070		$	101,714		$	87,328
Foreign	(20,588		)	(43,025		)	(78,612		)
Total	$	94,482		$	58,689		$	8,716

The provision (benefit) for income taxes consisted of the following (in thousands):



	For the Year Ended December 31,
	2018			2017			2016
Current:
Federal	$	(7,677	)	$	25,613		$	14,798
State	12,653			11,083			8,763
Foreign	4,781			4,589			9,844
	9,757			41,285			33,405
Deferred
Federal	19,899			(85,488		)	21,814
State	(1,205		)	1,085			1,644
Foreign	395			1,068			(8,274		)
	19,089			(83,335		)	15,184
Provision (benefit) for income taxes	$	28,846		$	(42,050	)	$	48,589

The Company's effective tax rate for fiscal years 2018, 2017 and 2016 was 30.5%, (71.6)% and 557.5%, respectively. The effective income tax rate varied from the amount computed using the statutory federal income tax rate as follows (in thousands):



	For the Year Ended December 31,
	2018			2017			2016
Tax expense at US statutory rate	$	19,841		$	20,541		$	3,051
State income taxes, net of federal benefit	8,711			4,547			6,010
Foreign rate differential	(1,124		)	3,733			3,646
Valuation allowance	10,466			16,552			22,564
Uncertain tax position interest and penalties	(1,806		)	3,730			107
Goodwill impairment	—			—			11,905
Tax credits	(9,799		)	—			—
Other	2,845			1,856			1,306
Adjustment for Tax Cuts and Jobs Act	(288		)	(93,009		)	—
Provision (benefit) for income taxes	$	28,846		$	(42,050	)	$	48,589

Effects of the Tax Cuts and Jobs Act. On December 22, 2017, the “Tax Cuts and Jobs Act” (the “Tax Act”) was signed into law, making significant changes to the federal tax law. Changes include, but are not limited to, a corporate tax rate decrease from 35% to 21% effective for tax years beginning after December 31, 2017, the transition of U.S. international taxation from a worldwide tax system to a territorial tax system, and a one-time transition tax on the mandatory deemed repatriation of cumulative foreign earnings as of December 31, 2017. For the year ended December 31, 2017, the Company calculated its best estimate of the impact of the Tax Act in its year end income tax provision in accordance with its understanding of the Tax Act and guidance available as of the date of the 2017 Form 10-K filing and as a result recorded a net benefit of $93.0 million as a component of the 2017 income tax expense. This provisional net income tax benefit was comprised of a $100.5 million tax benefit for the remeasurement of deferred tax assets and liabilities to the 21% rate at which they are expected to reverse, offset

(13) INCOME TAXES (Continued)

by a one-time tax expense on deemed repatriation of $7.5 million. This one-time charge was after the utilization of $7.5 million of foreign tax credits which had full valuation allowances applied to them previously.

During 2018, the Company completed its analysis of impacts of the Tax Act and specific to the one-time deemed repatriation, adjusted the previous amount recorded of $7.5 million to $6.6 million resulting in a $0.9 million benefit to tax expense recorded in 2018. The Company also recorded the final remeasurement of its deferred tax assets and liabilities and adjusted the deferred tax benefit from $100.5 million to $99.9 million or approximately $0.6 million of deferred expense recorded in 2018. The total net impact of changes in tax law resulted in a net benefit of approximately $0.3 million in 2018.

During 2018, the Company also completed an analysis of certain federal manufacturing and research and development credit benefits for tax years 2014 through 2017. Upon the filing of its 2017 tax return in October 2018, the Company recognized $3.3 million of tax benefits and recognized an additional $7.1 million upon the amendments of its 2014 through 2016 tax returns for a net benefit recorded as a component of the 2018 tax provision of $9.8 million.

During the year ended December 31, 2018, the Company recorded $5.0 million of tax benefits related to tax deductible foreign currency losses to accumulated other comprehensive loss and as such these benefits are not included within the provision (benefit) for income taxes.

The components of the total net deferred tax assets and liabilities at December 31, 2018 and 2017 were as follows (in thousands):



	2018			2017
Deferred tax assets:
Provision for doubtful accounts	$	10,715		$	7,417
Closure, post-closure and remedial liabilities	28,380			28,189
Accrued expenses	15,686			15,382
Accrued compensation	7,774			1,903
Net operating loss carryforwards(1)	43,284			46,650
Tax credit carryforwards(2)	16,909			17,504
Uncertain tax positions accrued interest and federal benefit	519			921
Stock-based compensation	3,440			2,268
Other	7,067			3,258
Total deferred tax assets	133,774			123,492
Deferred tax liabilities:
Property, plant and equipment	(164,246		)	(144,325		)
Permits and other intangible assets	(103,539		)	(107,407		)
Prepaids	(9,187		)	(8,080		)
Total deferred tax liabilities	(276,972		)	(259,812		)
Total net deferred tax liability before valuation allowance	(143,198		)	(136,320		)
Less valuation allowance	(79,295		)	(68,355		)
Net deferred tax liabilities	$	(222,493	)	$	(204,675	)

___________________________________


(1)	As of December 31, 2018, the net operating loss carryforwards included (i) state net operating loss carryovers of $185.1 million which will begin to expire in 2019, (ii) federal net operating loss carryforwards of $49.8 million which will begin to expire in 2025, and (iii) foreign net operating loss carryforwards of $103.3 million which will begin to expire in 2019.


(2)	As of December 31, 2018, the foreign tax credit carryforwards of $16.5 million will expire between 2020 and 2024.

(13) INCOME TAXES (Continued)

The Company has not accrued for any remaining undistributed foreign earnings not subject to the one-time transition tax on mandatory deemed repatriation of cumulative foreign earnings. These amounts continue to be indefinitely reinvested in foreign operations.

A valuation allowance is required to be established when, based on an evaluation of available evidence, it is more likely than not that some portion or all of the deferred tax assets will not be realized. Accordingly, as of December 31, 2018 and 2017, the Company had a valuation allowance of $79.3 million and $68.4 million, respectively. The total allowance as of December 31, 2018 consisted of $16.5 million of foreign tax credits, $0.8 million of acquired federal net operating losses, $9.6 million of state net operating loss carryforwards, $22.7 million of foreign net operating loss carryforwards, $26.6 million of deferred tax assets of a Canadian subsidiary and $3.1 million for tax attributes that if realized would generate capital losses. The allowance as of December 31, 2017 consisted of $17.5 million of foreign tax credits, $3.9 million of acquired federal net operating losses, $11.9 million of state net operating loss carryforwards and $22.6 million of foreign net operating loss carryforwards and $12.5 million of deferred tax assets of a Canadian subsidiary.

The changes to unrecognized tax benefits (excluding related penalties and interest) from January 1, 2016 through December 31, 2018, were as follows (in thousands):



	2018			2017			2016
Unrecognized tax benefits as of January 1	$	5,121		$	1,738		$	2,064
Additions to current year tax positions	—			1,457			—
(Reductions) additions to prior year tax positions	(625		)	2,031			—
Expirations	(1,115		)	(231		)	(533		)
Foreign currency translation	(222		)	126			207
Unrecognized tax benefits as of December 31	$	3,159		$	5,121		$	1,738

At December 31, 2018, 2017 and 2016, the Company had recorded $3.2 million, $5.1 million and $1.7 million, respectively, of unrecognized tax benefits that if recognized would affect the annual effective tax rate.

The Company's policy is to recognize interest and penalties related to income tax matters as a component of income tax expense. At December 31, 2018, 2017 and 2016 the Company has accrued interest of $0.8 million, $0.9 million and $0.3 million, respectively, relative to unrecognized tax benefits. Interest expense that is recorded as a tax expense against the liability for unrecognized tax benefits for the years ended December 31, 2018, 2017 and 2016 included interest and penalties of $(0.1) million, $0.5 million and $0.1 million, respectively.

The Company files U.S. federal income tax returns as well as income tax returns in various states and foreign jurisdictions. The Company may be subject to examination by the Internal Revenue Service (the "IRS") for calendar years 2014 through 2017. Additionally, any net operating losses that were generated in prior years and utilized in these years may also be subject to examination by the IRS. The Company may also be subject to examinations by state and local revenue authorities for calendar years 2013 through 2017. The Company is currently not under examination by the IRS. The Company has ongoing U.S. state and local jurisdictional audits, as well as Canadian federal and provincial audits, all of which the Company believes will not result in material liabilities.

Due to expiring statute of limitation periods and the resolution of tax audits, the Company believes that total unrecognized tax benefits will decrease by approximately $0.6 million within the next 12 months.

EARNINGS (LOSS) PER SHARE

12 Months Ended

Dec. 31, 2018

Earnings Per Share [Abstract]

EARNINGS (LOSS) PER SHARE

The following are computations of basic and diluted earnings (loss) per share (in thousands except for per share amounts):



	Years Ended December 31,
	2018		2017		2016
Numerator for basic and diluted earnings (loss) per share:
Net income (loss)	$	65,636	$	100,739	$	(39,873	)
Denominator:
Weighted basic shares outstanding	56,148		57,072		57,532
Dilutive effect of equity-based compensation awards	192		128		—
Weighted dilutive shares outstanding	56,340		57,200		57,532

Basic earnings (loss) per share	$	1.17	$	1.77	$	(0.69	)
Diluted earnings (loss) per share	$	1.16	$	1.76	$	(0.69	)

For the years ended December 31, 2018 and 2017, all then outstanding performance awards and restricted stock awards were included in the calculation of diluted earnings per share except for 79,390 and 152,831, respectively, of performance stock awards for which the performance criteria were not attained at the time and 121,803 and 49,373, respectively, of restricted stock awards which were excluded as their inclusion would have an antidilutive effect. As a result of the net loss reported for the year ended December 31, 2016, all outstanding stock options, restricted stock awards and performance awards, totaling 730,929 potentially dilutive shares, were excluded from the calculation of diluted loss per share as their inclusion would have an antidilutive effect.

STOCKHOLDERS' EQUITY	12 Months Ended
STOCKHOLDERS' EQUITY	Dec. 31, 2018
Equity [Abstract]
STOCKHOLDERS' EQUITY	STOCKHOLDERS' EQUITY The Company's board of directors has authorized the repurchase of up to $600 million of the Company's common stock. The Company has funded and intends to continue to fund the repurchases through available cash resources. The repurchase program authorizes the Company to purchase the Company's common stock on the open market or in privately negotiated transactions periodically in a manner that complies with applicable U.S. securities laws. The number of shares purchased and the timing of the purchases have depended and will depend on a number of factors including share price, cash required for future business plans, trading volume and other conditions. The Company has no obligation to repurchase stock under this program and may suspend or terminate the repurchase program at any time. During the years ended December 31, 2018, 2017 and 2016, the Company repurchased and retired a total of approximately 0.8 million, 0.9 million and 0.5 million shares, respectively, of the Company's common stock for total costs of approximately $45.1 million, $49.0 million and $22.2 million, respectively. Through December 31, 2018, the Company has repurchased and retired a total of approximately 5.6 million shares of its common stock for approximately $293.9 million under this program. As of December 31, 2018, an additional $306.1 million remained available for repurchase of shares under this program.

ACCUMULATED OTHER COMPREHENSIVE LOSS

12 Months Ended

Dec. 31, 2018

Equity [Abstract]

ACCUMULATED OTHER COMPREHENSIVE LOSS

The changes in accumulated other comprehensive loss by component and related tax effects for the years ended December 31, 2018, 2017 and 2016 were as follows (in thousands):



	Foreign Currency Translation Adjustments			Unrealized (Losses) Gains on Available-for-Sale Securities			Unrealized Loss on Interest Rate Hedge			Unfunded Pension Liability			Total
Balance at January 1, 2016	$	(252,939	)	$	—		$	—		$	(1,953	)	$	(254,892	)
Other comprehensive income (loss) before reclassifications	23,967			(535		)	—			216			23,648
Amounts reclassified out of accumulated other comprehensive loss	—			—			—			—			—
Tax benefit (loss)	16,761			214			—			(57		)	16,918
Other comprehensive income (loss)	40,728			(321		)	—			159			40,566
Balance at December 31, 2016	(212,211		)	(321		)	—			(1,794		)	(214,326		)
Other comprehensive income before reclassifications	41,636			184			—			146			41,966
Amounts reclassified out of accumulated other comprehensive loss	—			222			—			—			222
Tax loss	—			(231		)	—			(38		)	(269		)
Other comprehensive income	41,636			175			—			108			41,919
Balance at December 31, 2017	(170,575		)	(146		)	—			(1,686		)	(172,407		)
Other comprehensive (loss) income before tax effects	(47,374		)	182			(9,579		)	124			(56,647		)
Amounts reclassified out of accumulated other comprehensive loss	—			—			806			—			806
Tax benefit (loss)	5,024			(105		)	—			(42		)	4,877
Other comprehensive (loss) income	(42,350		)	77			(8,773		)	82			(50,964		)
Balance at December 31, 2018	$	(212,925	)	$	(69	)	$	(8,773	)	$	(1,604	)	$	(223,371	)

During the years ended December 31, 2018 and December 31, 2016, the Company converted intercompany loans with a foreign subsidiary to equity, which resulted in losses for tax purposes. The loans had been historically treated as components of the Company’s investments in that subsidiary, and as a result, foreign currency gains and losses on the loans had been accumulated as a component of other comprehensive (loss) income. The subsidiary continues to operate as part of the

Company. The tax benefits of $5.0 million and $16.8 million, respectively, which were triggered by the conversion, were therefore allocated to other comprehensive (loss) income rather than net income (loss).

The amounts reclassified out of accumulated other comprehensive loss into the consolidated statement of operations, with presentation location, during the years ended December 31, 2018 and 2017 were as follows (in thousands):



	For the years ended December 31,
Other Comprehensive Income Components	2018			2017			Location
Unrealized (losses) gains on available-for-sale securities	$	—		$	(222	)	Other (expense) income, net
Unrealized loss on interest rate hedge	(806		)	—			Interest expense, net of interest income

There were no reclassifications out of accumulated other comprehensive loss during the year ended December 31, 2016.

STOCK-BASED COMPENSATION AND EMPLOYEE BENEFIT PLANS

12 Months Ended

Dec. 31, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

STOCK-BASED COMPENSATION AND EMPLOYEE BENEFIT PLANS

STOCK-BASED COMPENSATION

Stock-Based Compensation

In 2010, the Company adopted an equity incentive plan (the "2010 Plan"), which provides for awards of up to 6,000,000 shares of common stock (subject to certain anti-dilution adjustments) in the form of (i) stock options, (ii) stock appreciation rights, (iii) restricted stock, (iv) restricted stock units, and (v) certain other stock-based awards. The Company ceased issuing

(17) STOCK-BASED COMPENSATION (Continued)

stock options in 2008, and all awards issued to date under the 2010 Plan have been in the form of restricted stock awards and performance stock awards as described below.

As of December 31, 2018 and 2017, the Company had the following types of stock-based compensation awards outstanding under the 2010 Plan: restricted stock awards and performance stock awards. The restricted stock awards generally vest over three to five years subject to continued employment. The performance stock awards vest depending on the satisfaction of certain performance criteria and continued service conditions as described below.

Total stock-based compensation cost charged to selling, general and administrative expenses for the years ended December 31, 2018, 2017 and 2016 was $16.8 million, $13.1 million and $10.5 million, respectively. The total income tax benefit recognized in the consolidated statements of operations from stock-based compensation was $3.2 million, $3.7 million and $2.8 million for the years ended December 31, 2018, 2017 and 2016, respectively.

Restricted Stock Awards

The following information relates to restricted stock awards that have been granted to employees and directors under the Company's 2010 Plan. The restricted stock awards are not transferable until vested and the restrictions generally lapse upon the achievement of continued employment over a three-to-five-year period or service as a director until the following annual meeting of shareholders. The fair value of each restricted stock grant is based on the closing price of the Company's common stock on the date of grant and is amortized to expense over its vesting period.

The following table summarizes information about restricted stock awards for the year ended December 31, 2018:



Restricted Stock	Number of Shares		Weighted Average Grant-Date Fair Value
Unvested at January 1, 2018	604,933		$	54.23
Granted	327,466		55.02
Vested	(198,673	)	54.22
Forfeited	(76,486	)	54.00
Unvested at December 31, 2018	657,240		$	54.65

As of December 31, 2018, there was $24.9 million of total unrecognized compensation cost arising from restricted stock awards. This cost is expected to be recognized over a weighted average period of 2.6 years. The total fair value of restricted stock vested during 2018, 2017 and 2016 was $10.8 million, $7.3 million and $8.3 million, respectively.

Performance Stock Awards

The following information relates to performance stock awards that have been granted to employees. The compensation committee of the Company's board of directors established two-year performance targets which could potentially be achieved in the year granted or one year thereafter. Performance stock awards are subject to performance criteria established by the compensation committee of the Company's board of directors. The vesting of the performance stock awards is based on achieving such targets typically based on revenue, Adjusted EBITDA margin, free cash flow and a measure of workplace safety. In addition, performance stock awards include continued service conditions.

The fair value of each performance stock award is based on the closing price of the Company's common stock on the date of grant and is amortized to expense over the service period if achievement of performance measures is then considered probable.

(17) STOCK-BASED COMPENSATION (Continued)

The following table summarizes information about performance stock awards for the year ended December 31, 2018:



Performance Stock	Number of Shares		Weighted Average Grant-Date Fair Value
Unvested at January 1, 2018	190,129		$	55.63
Granted	171,584		55.71
Vested	(21,416	)	54.82
Forfeited	(126,807	)	53.59
Unvested at December 31, 2018	213,490		$	55.71

As of December 31, 2018, there was $3.2 million of total unrecognized compensation cost arising from non-vested compensation related to performance stock awards then deemed probable of vesting under the Company's 2010 Plan. The total fair value of performance awards vested during 2018, 2017 and 2016 was $1.2 million, $3.0 million and $1.0 million, respectively.

COMMITMENTS AND CONTINGENCIES

12 Months Ended

Dec. 31, 2018

Commitments and Contingencies Disclosure [Abstract]

COMMITMENTS AND CONTINGENCIES

Legal and Administrative Proceedings

The Company and its subsidiaries are subject to legal proceedings and claims arising in the ordinary course of business. Actions filed against the Company arise from commercial and employment-related claims including alleged class actions related to sales practices and wage and hour claims. The plaintiffs in these actions may be seeking damages or injunctive relief

or both. These actions are in various jurisdictions and stages of proceedings, and some are covered in part by insurance. In addition, the Company’s waste management services operations are regulated by federal, state, provincial and local laws enacted to regulate discharge of materials into the environment, remediation of contaminated soil and groundwater or otherwise protect the environment. This ongoing regulation results in the Company frequently becoming a party to legal or administrative proceedings involving all levels of governmental authorities and other interested parties. The issues involved in such proceedings generally relate to alleged violations of existing permits and licenses or alleged responsibility under federal or state Superfund laws to remediate contamination at properties owned either by the Company or by other parties (“third-party sites”) to which either the Company or the prior owners of certain of the Company’s facilities shipped wastes.

At December 31, 2018 and December 31, 2017, the Company had recorded reserves of $25.4 million and $19.3 million, respectively, in the Company's financial statements for actual or probable liabilities related to the legal and administrative proceedings in which the Company was then involved, the principal of which are described below. At December 31, 2018 and December 31, 2017, the Company also believed that it was reasonably possible that the amount of these potential liabilities could be as much as $1.8 million more. The Company periodically adjusts the aggregate amount of these reserves when actual or probable liabilities are paid or otherwise discharged, new claims arise, or additional relevant information about existing or probable claims becomes available. As of December 31, 2018 and December 31, 2017, the $25.4 million and $19.3 million, respectively, of reserves consisted of (i) $17.9 million for each of the periods presented related to pending legal or administrative proceedings, including Superfund liabilities, which were included in remedial liabilities on the consolidated balance sheets, and (ii) $7.5 million and $1.4 million, respectively, primarily related to federal, state and provincial enforcement actions, which were included in accrued expenses on the consolidated balance sheets.

As of December 31, 2018, the principal legal and administrative proceedings in which the Company was involved, or which had been terminated during 2018, were as follows:

Ville Mercier. In September 2002, the Company acquired the stock of a subsidiary (the "Mercier Subsidiary") which owns a hazardous waste incinerator in Ville Mercier, Quebec (the "Mercier Facility"). The property adjacent to the Mercier Facility, which is also owned by the Mercier Subsidiary, is now contaminated as a result of actions dating back to 1968, when the Government of Quebec issued to a company unrelated to the Mercier Subsidiary two permits to dump organic liquids into lagoons on the property. In 1999, Ville Mercier and three neighboring municipalities filed separate legal proceedings against the Mercier Subsidiary and the Government of Quebec. In 2012, the municipalities amended their existing statement of claim to seek $2.9 million (CAD $) in general damages and $10.0 million (CAD $) in punitive damages, plus interest and costs, as well as injunctive relief. Both the Government of Quebec and the Company have filed summary judgment motions against the municipalities. The parties are attempting to negotiate a resolution and hearings on the motions have been delayed. In

(18) COMMITMENTS AND CONTINGENCIES (Continued)

September 2007, the Quebec Minister of Sustainable Development, Environment and Parks issued a notice pursuant to Section 115.1 of the Environment Quality Act, superseding notices issued in 1992, which are the subject of the pending litigation. The more recent notice notifies the Mercier Subsidiary that, if the Mercier Subsidiary does not take certain remedial measures at the site, the Minister intends to undertake those measures at the site and claim direct and indirect costs related to such measures. The Company has accrued for costs expected to be incurred relative to the resolution of this matter and believes this matter will not have future material effect on its financial position or results of operations.

Safety-Kleen Legal Proceedings. On December 28, 2012, the Company acquired Safety-Kleen, Inc. ("Safety-Kleen") and thereby became subject to the legal proceedings in which Safety-Kleen was a party on that date. In addition to certain Superfund proceedings in which Safety-Kleen has been named as a potentially responsible party as described below under “Superfund Proceedings,” the principal such legal proceedings involving Safety-Kleen which were outstanding as of December 31, 2018 were as follows:

Product Liability Cases. Safety-Kleen has been named as a defendant in various lawsuits that are currently pending in various courts and jurisdictions throughout the United States, including approximately 67 proceedings (excluding cases which have been settled but not formally dismissed) as of December 31, 2018, wherein persons claim personal injury resulting from the use of Safety-Kleen's parts cleaning equipment or cleaning products. These proceedings typically involve allegations that the solvent used in Safety-Kleen's parts cleaning equipment contains contaminants and/or that Safety-Kleen's recycling process does not effectively remove the contaminants that become entrained in the solvent during their use. In addition, certain claimants assert that Safety-Kleen failed to warn adequately the product user of potential risks, including a historic failure to warn that solvent contains trace amounts of toxic or hazardous substances such as benzene.

Safety-Kleen maintains insurance that it believes will provide coverage for these product liability claims (over amounts accrued for self-insured retentions and deductibles in certain limited cases), except for punitive damages to the extent not insurable under state law or excluded from insurance coverage. Safety-Kleen also believes that these claims lack merit and has historically vigorously defended, and intends to continue to vigorously defend, itself and the safety of its products against all of these claims. Such matters are subject to many uncertainties and outcomes are not predictable with assurance. Consequently, Safety-Kleen is unable to ascertain the ultimate aggregate amount of monetary liability or financial impact with respect to these matters as of December 31, 2018. From January 1, 2018 to December 31, 2018, 10 product liability claims were settled or dismissed. Due to the nature of these claims and the related insurance, the Company did not incur any expense as Safety-Kleen's insurance provided coverage in full for all such claims. Safety-Kleen may be named in similar, additional lawsuits in the future, including claims for which insurance coverage may not be available.

Superfund Proceedings

The Company has been notified that either the Company (which, since December 28, 2012, includes Safety-Kleen) or the prior owners of certain of the Company's facilities for which the Company may have certain indemnification obligations have been identified as potentially responsible parties ("PRPs") or potential PRPs in connection with 128 sites which are subject to or

are proposed to become subject to proceedings under federal or state Superfund laws. Of the 128 sites, five (including the BR Facility described below) involve facilities that are now owned or leased by the Company and 123 involve third-party sites to which either the Company or the prior owners of certain of the Company’s facilities shipped wastes. Of the 123 third-party sites, 30 are now settled, 16 are currently requiring expenditures on remediation and 77 are not currently requiring expenditures on remediation.

In connection with each site, the Company has estimated the extent, if any, to which it may be subject, either directly or as a result of any indemnification obligations, for cleanup and remediation costs, related legal and consulting costs associated with PRP investigations, settlements, and related legal and administrative proceedings. The amount of such actual and potential liability is inherently difficult to estimate because of, among other relevant factors, uncertainties as to the legal liability (if any) of the Company or the prior owners of certain of the Company's facilities to contribute a portion of the cleanup costs, the assumptions that must be made in calculating the estimated cost and timing of remediation, the identification of other PRPs and their respective capability and obligation to contribute to remediation efforts, and the existence and legal standing of indemnification agreements (if any) with prior owners, which may either benefit the Company or subject the Company to potential indemnification obligations. The Company believes its potential liability could exceed $100,000 at 12 of the 123 third-party sites.

(18) COMMITMENTS AND CONTINGENCIES (Continued)

BR Facility. The Company acquired in 2002 a former hazardous waste incinerator and landfill in Baton Rouge (the "BR Facility"), for which operations had been previously discontinued by the prior owner. In September 2007, the EPA issued a special notice letter to the Company related to the Devil's Swamp Lake Site ("Devil's Swamp") in East Baton Rouge Parish, Louisiana. Devil's Swamp includes a lake located downstream of an outfall ditch where wastewater and storm water have been discharged, and Devil's Swamp is proposed to be included on the National Priorities List due to the presence of Contaminants of Concern ("COC") cited by the EPA. These COCs include substances of the kind found in wastewater and storm water discharged from the BR Facility in past operations. The EPA originally requested COC generators to submit a good faith offer to conduct a remedial investigation feasibility study directed towards the eventual remediation of the site. In 2018 the Company completed performing corrective actions at the BR Facility under an order issued by the Louisiana Department of Environmental Quality, and has also completed conducting the remedial investigation and feasibility study for Devil's Swamp under an order issued by the EPA. The Company cannot presently estimate the potential additional liability for the Devil's Swamp cleanup until a final remedy is selected by the EPA with issuance of a Record of Decision.

Third-Party Sites. Of the 123 third-party sites at which the Company has been notified it is a PRP or potential PRP or may have indemnification obligations, Clean Harbors has an indemnification agreement at 11 of these sites with ChemWaste, a former subsidiary of Waste Management, Inc., and at six additional of these third-party sites, Safety-Kleen has a similar indemnification agreement with McKesson Corporation. These agreements indemnify the Company (which now includes Safety-Kleen) with respect to any liability at the 17 sites for waste disposed prior to the Company's (or Safety-Kleen's) acquisition of the former subsidiaries of Waste Management and McKesson which had shipped wastes to those sites. Accordingly, Waste Management or McKesson are paying all costs of defending those subsidiaries in those 17 cases, including legal fees and settlement costs. However, there can be no guarantee that the Company's ultimate liabilities for those sites will not exceed the amount recorded or that indemnities applicable to any of these sites will be available to pay all or a portion of related costs. Except for the indemnification agreements which the Company holds from ChemWaste, McKesson and two other entities, the Company does not have an indemnity agreement with respect to any of the 123 third-party sites discussed above.

Federal, State and Provincial Enforcement Actions

From time to time, the Company pays fines or penalties in regulatory proceedings relating primarily to waste treatment, storage or disposal facilities. As of December 31, 2018 and 2017, there were ten and five proceedings, respectively, for which the Company reasonably believes that the sanctions could equal or exceed $100,000. The Company believes that the fines or other penalties in these or any of the other regulatory proceedings will, individually or in the aggregate, not have a material effect on its financial condition, results of operations or cash flows.

Leases

The Company leases facilities, service centers and personal property under certain operating leases. Some of these lease agreements contain an escalation clause for increased taxes and operating expenses and are renewable at the option of the Company. Lease terms range from 1 to 25 years. The following is a summary of future minimum payments under operating leases that have initial or remaining non-cancelable lease terms in excess of one year at December 31, 2018 (in thousands):



Year	Total Operating Leases
2019	$	56,480
2020	45,467
2021	33,564
2022	24,509
2023	15,253
Thereafter	35,778
Total minimum lease payments	$	211,051

During the years ended December 31, 2018, 2017 and 2016, rent expense including short-term rentals was approximately $141.1 million, $125.4 million, and $121.9 million, respectively.

(18) COMMITMENTS AND CONTINGENCIES (Continued)

Other Contingencies

Under the Company's insurance programs, coverage is obtained for catastrophic exposures, as well as those risks required to be insured by law or contract. The Company's policy is to retain a significant portion of certain expected losses related to workers' compensation, health insurance, comprehensive general liability and vehicle liability. A portion of these self-insured liabilities are managed through its wholly-owned captive insurance subsidiary.

Provisions for losses expected under these programs are recorded based upon the Company's estimates of the aggregate liability for claims. The current deductible per participant per year for the health insurance policy is $0.7 million. The current deductible per occurrence for workers' compensation is $1.0 million, general liability is $2.0 million and vehicle liability is $2.0 million. The retention per claim for the environmental impairment policy is $1.0 million. At December 31, 2018 and 2017, the Company had accrued $53.9 million and $47.9 million, respectively, for its self-insurance liabilities (exclusive of health insurance) using a risk-free discount rate of 2.96% and 1.87%, respectively. A significant portion of the increase in the liabilities as of December 31, 2018 is attributable to amounts assumed in connection with the acquisition of the Veolia Business which occurred in 2018. Actual expenditures in future periods can differ materially from accruals based on estimates.

Anticipated payments for contingencies related to workers' compensation, comprehensive general liability and vehicle liability related claims at December 31, 2018 for each of the next five years and thereafter were as follows (in thousands):



Years ending December 31,
2019	$	20,171
2020	12,799
2021	7,964
2022	4,992
2023	4,082
Thereafter	6,385
Undiscounted self-insurance liabilities	56,393
Less: Discount	2,492
Total self-insurance liabilities (included in accrued expenses)	$	53,901

SEGMENT REPORTING

12 Months Ended

Dec. 31, 2018

Segment Reporting [Abstract]

SEGMENT REPORTING

Segment reporting is prepared on the same basis that the Company's chief executive officer, who is the Company's chief operating decision maker, manages the business, makes operating decisions and assesses performance. During the first quarter of fiscal year 2018, certain of the Company's businesses undertook a reorganization which included changes to the underlying business and management structures. The reorganization resulted in combining the Environmental Services businesses from an operational and management perspective, deepening customer relationships and allowing for efficiencies across the Company's operations through the sharing of resources, namely labor and equipment, which will reduce third party spending and promote cross selling of such business offerings. In connection with this reorganization, the Company’s chief operating decision maker requested changes in the information that he regularly reviews for purposes of allocating resources and assessing performance. These changes required a reconsideration of the Company’s operating segments in the first quarter of 2018 and resulted in a change in the Company’s assessment of its operating segments. Upon reconsideration of the identification of the Company’s operating segments, the Company concluded that there are now two operating segments for disclosure purposes; (i) the Environmental Services segment which consists of the Company’s historical Technical Services, Industrial Services, Field Services and Oil, Gas and Lodging businesses, and (ii) the Safety-Kleen segment. The amounts presented for the years ended December 31, 2017 and 2016 have been reclassified to conform to the new segment presentation. These reclassifications and adjustments had no effect on the consolidated statements of operations, consolidated statements of comprehensive income, consolidated statements of cash flows or consolidated statements of stockholders' equity for any of the periods presented.

Third-party revenue is revenue billed to outside customers by a particular segment. Direct revenue is revenue allocated to the segment providing the product or service. Intersegment revenues represent the sharing of third-party revenues among the segments based on products and services provided by each segment as if the products and services were sold directly to the third-party. The intersegment revenues are shown net. The operations not managed through the Company’s operating segments described above are recorded as “Corporate Items.”

(19) SEGMENT REPORTING (Continued)

The following table reconciles third-party revenues to direct revenues for the years ended December 31, 2018, 2017 and 2016 (in thousands):



	For the Year Ended December 31, 2018
	Environmental Services		Safety-Kleen			Corporate Items			Totals
Third-party revenues	$	2,003,843	$	1,295,355		$	1,105		$	3,300,303
Intersegment revenues, net	134,104		(134,104		)	—			—
Corporate Items, net	3,247		31			(3,278		)	—
Direct revenues	$	2,141,194	$	1,161,282		$	(2,173	)	$	3,300,303



	For the Year Ended December 31, 2017
	Environmental Services		Safety-Kleen			Corporate Items			Totals
Third-party revenues	$	1,728,700	$	1,213,703		$	2,575		$	2,944,978
Intersegment revenues, net	125,822		(125,822		)	—			—
Corporate Items, net	2,952		5			(2,957		)	—
Direct revenues	$	1,857,474	$	1,087,886		$	(382	)	$	2,944,978



	For the Year Ended December 31, 2016
	Environmental Services		Safety-Kleen			Corporate Items			Totals
Third-party revenues	$	1,641,432	$	1,110,727		$	3,067		$	2,755,226
Intersegment revenues, net	115,013		(115,013		)	—			—
Corporate Items, net	2,388		369			(2,757		)	—
Direct revenues	$	1,758,833	$	996,083		$	310		$	2,755,226

The primary financial measure by which the Company evaluates the performance of its segments is Adjusted EBITDA, which consists of net income (loss) plus accretion of environmental liabilities, depreciation and amortization, net interest expense, loss on early extinguishment of debt, provision (benefit) for income taxes, other gains or non-cash charges (including gain on sale of businesses and goodwill impairment charge) not deemed representative of fundamental segment results and excludes other expense (income), net. Transactions between the segments are accounted for at the Company’s best estimate based on similar transactions with outside customers.

(19) SEGMENT REPORTING (Continued)

The following table presents Adjusted EBITDA information used by management by reported segment (in thousands):



	For the Year Ended December 31,
	2018			2017			2016
Adjusted EBITDA:
Environmental Services	$	380,856		$	321,310		$	319,075
Safety-Kleen	282,029			249,811			219,546
Corporate Items	(171,880		)	(145,464		)	(138,267		)
Total	491,005			425,657			400,354
Reconciliation to Consolidated Statements of Operations:
Accretion of environmental liabilities	9,806			9,460			10,177
Depreciation and amortization	298,625			288,422			287,002
Goodwill impairment charge	—			—			34,013
Income from operations	182,574			127,775			69,162
Other expense (income), net	4,510			6,119			(6,195		)
Loss on early extinguishment of debt	2,488			7,891			—
Gain on sale of businesses	—			(30,732		)	(16,884		)
Interest expense, net of interest income	81,094			85,808			83,525
Income from operations before provision (benefit) for income taxes	$	94,482		$	58,689		$	8,716

Geographical Information

For the years ended December 31, 2018, 2017, and 2016, the Company generated direct revenues in the following geographic locations (in thousands):



	For the Year Ended December 31,
	2018				2017				2016
	Revenue		% of Total		Revenue		% of Total		Revenue		% of Total
United States	$	2,721,814	82.5	%	$	2,392,000	81.2	%	$	2,213,355	80.3	%
Canada	578,489		17.5	%	552,978		18.8	%	541,871		19.7	%
Total Revenues	$	3,300,303	100.0	%	$	2,944,978	100.0	%	$	2,755,226	100.0	%

As of December 31, 2018 and 2017, the Company had property, plant and equipment, net of depreciation and amortization and permits and other intangible assets in the following geographic locations (in thousands):



	For the Year Ended December 31,
	2018				2017
	Total		% of Total		Total		% of Total
Property, plant and equipment, net
United States	$	1,233,949	79.0	%	$	1,175,437	74.0	%
Canada	328,029		21.0	%	411,928		26.0	%
Total property, plant and equipment, net	$	1,561,978	100.0	%	$	1,587,365	100.0	%

Permits and other intangibles, net
United States	$	393,045	88.9	%	$	408,654	87.1	%
Canada	48,830		11.1	%	60,474		12.9	%
Total permits and other intangibles, net	$	441,875	100.0	%	$	469,128	100.0	%

(19) SEGMENT REPORTING (Continued)

The following table presents assets by reported segment and in the aggregate (in thousands):



	December 31, 2018		December 31, 2017
Property, plant and equipment, net
Environmental Services	$	951,867	$	927,139
Safety-Kleen	553,220		582,162
Corporate Items	56,891		78,064
Total property, plant and equipment, net	$	1,561,978	$	1,587,365

Goodwill and Permits and other intangibles, net
Environmental Services
Goodwill	$	207,019	$	172,386
Permits and other intangibles, net	93,313		97,519
Total Environmental Services	300,332		269,905

Safety-Kleen
Goodwill	$	307,170	$	306,137
Permits and other intangibles, net	348,562		371,609
Total Safety-Kleen	655,732		677,746

Total	$	956,064	$	947,651

The following table presents the total assets by reported segment (in thousands):



	December 31, 2018		December 31, 2017
Environmental Services	$	1,640,706	$	1,541,241
Safety-Kleen	1,431,381		1,471,291
Corporate Items	666,234		694,038
Total	$	3,738,321	$	3,706,570

The following table presents the total assets by geographical area (in thousands):



	December 31, 2018		December 31, 2017
United States	$	3,090,311	$	2,985,394
Canada	648,010		721,176
Total	$	3,738,321	$	3,706,570

GUARANTOR AND NON-GUARANTOR SUBSIDIARIES

12 Months Ended

Dec. 31, 2018

Guarantor and Non-Guarantor Subsidiaries Financial Information [Abstract]

GUARANTOR AND NON-GUARANTOR SUBSIDIARIES

The previously outstanding 2020 Notes and the currently outstanding 2021 Notes (collectively, the "Senior Unsecured Notes") and the Company's obligations under its Term Loan Agreement were or are guaranteed by substantially all of the Company’s subsidiaries organized in the United States. Each guarantor was or is a 100% owned subsidiary of Clean Harbors, Inc. and its guarantee was or is both full and unconditional and joint and several. The guarantees were or are, however, subject to customary release provisions under which, in particular, the guarantee of any domestic restricted subsidiary will be released if the Company sells such subsidiary to an unrelated third party in accordance with the terms of the indentures which govern the Senior Unsecured Notes and of the Term Loan Agreement. The Senior Unsecured Notes and the Company's obligations under its Term Loan Agreement are not guaranteed by the Company’s subsidiaries organized outside the United States. The following supplemental condensed consolidating financial information for the parent company, the guarantor subsidiaries and the non-guarantor subsidiaries, respectively, is presented in conformity with the requirements of Rule 3-10 of SEC Regulation S-X (“Rule 3-10”).

(20) GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Continued)

Following is the condensed consolidating balance sheet at December 31, 2018 (in thousands):



	Clean Harbors, Inc.		Guarantor Subsidiaries		Non-Guarantor Subsidiaries		Consolidating Adjustments			Total
Assets:
Cash and cash equivalents	$	27,308	$	101,302	$	97,897	$	—		$	226,507
Short-term marketable securities	67		—		52,789		—			52,856
Intercompany receivables	262,475		721,521		60,693		(1,044,689		)	—
Accounts receivable, net	—		520,785		86,167		—			606,952
Other current assets	—		289,869		49,631		(23,657		)	315,843
Property, plant and equipment, net	—		1,233,578		328,400		—			1,561,978
Investments in subsidiaries	3,162,704		571,304		—		(3,734,008		)	—
Intercompany debt receivable	—		14,669		21,000		(35,669		)	—
Goodwill	—		456,307		57,882		—			514,189
Permits and other intangibles, net	—		393,045		48,830		—			441,875
Other long-term assets	1,551		13,545		3,025		—			18,121
Total assets	$	3,454,105	$	4,315,925	$	806,314	$	(4,838,023	)	$	3,738,321
Liabilities and Stockholders' Equity:
Current liabilities	$	20,170	$	457,164	$	148,601	$	(23,657	)	$	602,278
Intercompany payables	699,158		321,846		23,685		(1,044,689		)	—
Closure, post-closure and remedial liabilities, net	—		151,480		16,434		—			167,914
Long-term obligations	1,565,021		—		—		—			1,565,021
Intercompany debt payable	—		21,000		14,669		(35,669		)	—
Other long-term liabilities	—		212,924		20,428		—			233,352
Total liabilities	2,284,349		1,164,414		223,817		(1,104,015		)	2,568,565
Stockholders' equity	1,169,756		3,151,511		582,497		(3,734,008		)	1,169,756
Total liabilities and stockholders' equity	$	3,454,105	$	4,315,925	$	806,314	$	(4,838,023	)	$	3,738,321

(20) GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Continued)

Following is the condensed consolidating balance sheet at December 31, 2017 (in thousands):



	Clean Harbors, Inc.		Guarantor Subsidiaries		Non-Guarantor Subsidiaries		Consolidating Adjustments			Total
Assets:
Cash and cash equivalents	$	51,638	$	207,777	$	59,984	$	—		$	319,399
Short-term marketable securities	—		—		38,179		—			38,179
Intercompany receivables	238,339		590,100		52,909		(881,348		)	—
Accounts receivable, net	—		433,042		95,882		—			528,924
Other current assets	897		233,602		52,947		(19,892		)	267,554
Property, plant and equipment, net	—		1,174,975		412,390		—			1,587,365
Investments in subsidiaries	3,112,547		569,568		—		(3,682,115		)	—
Intercompany debt receivable	—		92,530		21,000		(113,530		)	—
Goodwill	—		415,641		62,882		—			478,523
Permits and other intangibles, net	—		408,655		60,473		—			469,128
Other long-term assets	2,084		12,064		3,350		—			17,498
Total assets	$	3,405,505	$	4,137,954	$	859,996	$	(4,696,885	)	$	3,706,570
Liabilities and Stockholders' Equity:
Current liabilities	$	16,954	$	371,135	$	135,620	$	(19,892	)	$	503,817
Intercompany payables	574,812		289,531		17,005		(881,348		)	—
Closure, post-closure and remedial liabilities, net	—		148,872		16,851		—			165,723
Long-term obligations	1,625,537		—		—		—			1,625,537
Intercompany debt payable	—		21,000		92,530		(113,530		)	—
Other long-term liabilities	—		201,086		22,205		—			223,291
Total liabilities	2,217,303		1,031,624		284,211		(1,014,770		)	2,518,368
Stockholders' equity	1,188,202		3,106,330		575,785		(3,682,115		)	1,188,202
Total liabilities and stockholders' equity	$	3,405,505	$	4,137,954	$	859,996	$	(4,696,885	)	$	3,706,570

(20) GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Continued)

Following is the consolidating statement of operations for the year ended December 31, 2018 (in thousands):



	Clean Harbors, Inc.			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating Adjustments			Total
Revenues
Service revenues	$	—		$	2,145,310		$	621,435		$	(57,506	)	$	2,709,239
Product revenues	—			537,400			66,210			(12,546		)	591,064
Total revenues	—			2,682,710			687,645			(70,052		)	3,300,303
Cost of revenues (exclusive of items shown separately below)
Service cost of revenues	—			1,421,693			497,788			(57,506		)	1,861,975
Product cost of revenues	—			419,377			36,745			(12,546		)	443,576
Total cost of revenues	—			1,841,070			534,533			(70,052		)	2,305,551
Selling, general and administrative expenses	347			419,984			83,416			—			503,747
Accretion of environmental liabilities	—			8,797			1,009			—			9,806
Depreciation and amortization	—			219,530			79,095			—			298,625
(Loss) income from operations	(347		)	193,329			(10,408		)	—			182,574
Other expense, net	(1,384		)	(1,284		)	(1,842		)	—			(4,510		)
Loss on early extinguishment of debt	(2,488		)	—			—			—			(2,488		)
Interest (expense) income, net	(83,362		)	1,252			1,016			—			(81,094		)
Equity in earnings of subsidiaries, net of tax	129,082			(25,765		)	—			(103,317		)	—
Intercompany interest income (expense)	—			2,841			(2,841		)	—			—
Income (loss) before (benefit) provision for income taxes	41,501			170,373			(14,075		)	(103,317		)	94,482
(Benefit) provision for income taxes	(24,135		)	46,267			6,714			—			28,846
Net income (loss)	65,636			124,106			(20,789		)	(103,317		)	65,636
Other comprehensive loss	(50,964		)	(50,964		)	(44,292		)	95,256			(50,964		)
Comprehensive income (loss)	$	14,672		$	73,142		$	(65,081	)	$	(8,061	)	$	14,672

(20) GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Continued)

Following is the consolidating statement of operations for the year ended December 31, 2017 (in thousands):



	Clean Harbors, Inc.			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating Adjustments			Total
Revenues
Service revenues	$	—		$	1,870,256		$	582,042		$	(53,648	)	$	2,398,650
Product revenues	—			492,036			66,511			(12,219		)	546,328
Total revenues	—			2,362,292			648,553			(65,867		)	2,944,978
Cost of revenues (exclusive of items shown separately below)
Service cost of revenues	—			1,224,326			471,120			(53,648		)	1,641,798
Product cost of revenues	—			386,455			46,639			(12,219		)	420,875
Total cost of revenues	—			1,610,781			517,759			(65,867		)	2,062,673
Selling, general and administrative expenses	—			373,050			83,598			—			456,648
Accretion of environmental liabilities	—			8,479			981			—			9,460
Depreciation and amortization	—			205,034			83,388			—			288,422
Income (loss) from operations	—			164,948			(37,173		)	—			127,775
Other expense, net	(222		)	(5,156		)	(741		)	—			(6,119		)
Loss on early extinguishment of debt	(7,891		)	—			—			—			(7,891		)
Gain on sale of business	—			30,732			—			—			30,732
Interest (expense) income, net	(87,113		)	1,523			(218		)	—			(85,808		)
Equity in earnings of subsidiaries, net of tax	157,963			(48,683		)	—			(109,280		)	—
Intercompany interest income (expense)	—			5,288			(5,288		)	—			—
Income (loss) before (benefit) provision for income taxes	62,737			148,652			(43,420		)	(109,280		)	58,689
(Benefit) provision for income taxes	(38,002		)	(10,117		)	6,069			—			(42,050		)
Net income (loss)	100,739			158,769			(49,489		)	(109,280		)	100,739
Other comprehensive income	41,919			41,919			38,131			(80,050		)	41,919
Comprehensive income (loss)	$	142,658		$	200,688		$	(11,358	)	$	(189,330	)	$	142,658

20) GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Continued)

Following is the consolidating statement of operations for the year ended December 31, 2016 (in thousands):



	Clean Harbors, Inc.			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating Adjustments			Total
Revenues
Service revenues	$	—		$	1,747,985		$	582,075		$	(49,251	)	$	2,280,809
Product revenues	—			410,868			73,793			(10,244		)	474,417
Total revenues	—			2,158,853			655,868			(59,495		)	2,755,226
Cost of revenues (exclusive of items shown separately below)
Service cost of revenues	—			1,116,132			476,329			(49,251		)	1,543,210
Product cost of revenues	—			349,069			50,822			(10,244		)	389,647
Total cost of revenues	—			1,465,201			527,151			(59,495		)	1,932,857
Selling, general and administrative expenses	85			341,963			79,967			—			422,015
Accretion of environmental liabilities	—			9,261			916			—			10,177
Depreciation and amortization	—			201,153			85,849			—			287,002
Goodwill impairment charge	—			—			34,013			—			34,013
(Loss) income from operations	(85		)	141,275			(72,028		)	—			69,162
Other income (expense), net	—			7,713			(1,518		)	—			6,195
Gain on sale of business	—			1,704			15,180			—			16,884
Interest (expense) income, net	(88,984		)	5,391			68			—			(83,525		)
Equity in earnings of subsidiaries, net of tax	13,568			(80,244		)	—			66,676			—
Intercompany interest income (expense)	—			19,855			(19,855		)	—			—
(Loss) income before (benefit) provision for income taxes	(75,501		)	95,694			(78,153		)	66,676			8,716
(Benefit) provision for income taxes	(35,628		)	82,643			1,574			—			48,589
Net (loss) income	(39,873		)	13,051			(79,727		)	66,676			(39,873		)
Other comprehensive income	40,566			40,566			15,291			(55,857		)	40,566
Comprehensive income (loss)	$	693		$	53,617		$	(64,436	)	$	10,819		$	693

(20) GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Continued)

Following is the condensed consolidating statement of cash flows for the year ended December 31, 2018 (in thousands):



	Clean Harbors, Inc.			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating Adjustments			Total
Net cash from operating activities	$	34,135		$	260,101		$	78,974		$	—		$	373,210
Cash flows used in investing activities:
Additions to property, plant and equipment	—			(161,342		)	(32,002		)	—			(193,344		)
Proceeds from sale and disposal of fixed assets	—			4,174			11,271			—			15,445
Proceeds from sale of available-for-sale securities	—			—			28,723			—			28,723
Acquisitions, net of cash acquired	—			(151,023		)	—			—			(151,023		)
Additions to intangible assets, including costs to obtain or renew permits	—			(4,326		)	(362		)	—			(4,688		)
Purchases of available-for-sale securities	(1,450		)	—			(43,322		)	—			(44,772		)
Intercompany	—			(54,114		)	—			54,114			—
Net cash used in investing activities	(1,450		)	(366,631		)	(35,692		)	54,114			(349,659		)
Cash flows (used in) from financing activities:
Change in uncashed checks	—			55			77			—			132
Tax payments related to withholdings on vested restricted stock	(3,266		)	—			—			—			(3,266		)
Deferred financing costs paid	(4,027		)	—			—			—			(4,027		)
Repurchases of common stock	(45,080		)	—			—			—			(45,080		)
Principal payments on debt	(405,768		)	—			—			—			(405,768		)
Premium paid on early extinguishment of debt	(1,238		)	—			—			—			(1,238		)
Issuance of senior secured notes, net of discount	348,250			—			—			—			348,250
Borrowing from revolving credit facility	50,000			—			—			—			50,000
Payment on revolving credit facility	(50,000		)	—			—			—			(50,000		)
Intercompany	54,114			—			—			(54,114		)	—
Net cash (used in) from financing activities	(57,015		)	55			77			(54,114		)	(110,997		)
Effect of exchange rate change on cash	—			—			(5,446		)	—			(5,446		)
(Decrease) increase in cash and cash equivalents	(24,330		)	(106,475		)	37,913			—			(92,892		)
Cash and cash equivalents, beginning of year	51,638			207,777			59,984			—			319,399
Cash and cash equivalents, end of year	$	27,308		$	101,302		$	97,897		$	—		$	226,507

(20) GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Continued)

Following is the condensed consolidating statement of cash flows for the year ended December 31, 2017 (in thousands):



	Clean Harbors, Inc.			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating Adjustments			Total
Net cash from operating activities	$	16,292		$	217,001		$	52,405		$	—		$	285,698
Cash flows from (used in) investing activities:
Additions to property, plant and equipment	—			(142,211		)	(24,796		)	—			(167,007		)
Proceeds from sale and disposal of fixed assets	—			1,979			5,145			—			7,124
Proceeds from sale of available-for-sale securities	376			—			—			—			376
Proceeds from sale of business, net of transactional costs	—			45,245			181			—			45,426
Acquisitions, net of cash acquired	—			(11,427		)	(37,800		)	—			(49,227		)
Additions to intangible assets, including costs to obtain or renew permits	—			(1,153		)	(464		)	—			(1,617		)
Purchases of available-for-sale securities	—			—			(38,342		)	—			(38,342		)
Intercompany	—			(54,074		)	—			54,074			—
Intercompany debt	—			—			3,701			(3,701		)	—
Net cash from (used in) investing activities	376			(161,641		)	(92,375		)	50,373			(203,267		)
Cash flows used in financing activities:
Change in uncashed checks	—			(3,526		)	(2,414		)	—			(5,940		)
Proceeds from exercise of stock options	46			—			—			—			46
Tax payments related to withholdings on vested restricted stock	(3,149		)	—			—			—			(3,149		)
Deferred financing costs paid	(5,718		)	—			—			—			(5,718		)
Repurchases of common stock	(48,971		)	—			—			—			(48,971		)
Principal payments on debt	(402,000		)	—			—			—			(402,000		)
Premium paid on early extinguishment of debt	(6,028		)	—			—			—			(6,028		)
Issuance of senior secured notes, net of discount	399,000			—			—			—			399,000
Intercompany	54,074			—			—			(54,074		)	—
Intercompany debt	(3,701		)	—			—			3,701			—
Net cash used in financing activities	(16,447		)	(3,526		)	(2,414		)	(50,373		)	(72,760		)
Effect of exchange rate change on cash	—			—			2,731			—			2,731
Increase (decrease) in cash and cash equivalents	221			51,834			(39,653		)	—			12,402
Cash and cash equivalents, beginning of year	51,417			155,943			99,637			—			306,997
Cash and cash equivalents, end of year	$	51,638		$	207,777		$	59,984		$	—		$	319,399

(20) GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Continued)

Following is the condensed consolidating statement of cash flows for the year ended December 31, 2016 (in thousands):



	Clean Harbors, Inc.			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating Adjustments			Total
Net cash from operating activities	$	51,033		$	125,591		$	83,000		$	—		$	259,624
Cash flows used in investing activities:
Additions to property, plant and equipment	—			(194,184		)	(25,200		)	—			(219,384		)
Proceeds from sale and disposal of fixed assets	—			12,926			7,891			—			20,817
Proceeds on sale of business, net of transactional costs	—			18,885			28,249			—			47,134
Acquisitions, net of cash acquired	—			(196,915		)	(10,000		)	—			(206,915		)
Additions to intangible assets including costs to obtain or renew permits	—			(1,749		)	(1,082		)	—			(2,831		)
Purchases of available-for-sale securities	(102		)	—			(496		)	—			(598		)
Intercompany	—			(23,182		)	—			23,182			—
Intercompany debt	—			63,118			(21,000		)	(42,118		)	—
Investment in subsidiaries	(257,125		)	—			—			257,125			—
Net cash used in investing activities	(257,227		)	(321,101		)	(21,638		)	238,189			(361,777		)
Cash flows from (used in) financing activities:
Change in uncashed checks	—			(3,651		)	474			—			(3,177		)
Proceeds from exercise of stock options	627			—			—			—			627
Tax payments related to withholdings on vested restricted stock	(2,819		)	—			—			—			(2,819		)
Deferred financing costs paid	(4,031		)	—			—			—			(4,031		)
Repurchases of common stock	(22,188		)	—			—			—			(22,188		)
Excess tax benefit of stock-based compensation	1,198			—			—			—			1,198
Issuance of senior unsecured notes, including premium	250,625			250,625			—			(250,625		)	250,625
Intercompany	23,182			—			6,500			(29,682		)	—
Intercompany debt	—			21,000			(63,118		)	42,118			—
Net cash from (used in) financing activities	246,594			267,974			(56,144		)	(238,189		)	220,235
Effect of exchange rate change on cash	—			—			4,207			—			4,207
Increase in cash and cash equivalents	40,400			72,464			9,425			—			122,289
Cash and cash equivalents, beginning of year	11,017			83,479			90,212			—			184,708
Cash and cash equivalents, end of year	$	51,417		$	155,943		$	99,637		$	—		$	306,997

QUARTERLY DATA (UNAUDITED)

12 Months Ended

Dec. 31, 2018

Quarterly Financial Information Disclosure [Abstract]

QUARTERLY DATA (UNAUDITED)



	First Quarter			Second Quarter		Third Quarter			Fourth Quarter
	(in thousands except per share amounts)
2018
Revenues	$	749,778		$	849,140	$	843,181		$	858,204
Cost of revenues (1)	546,425			583,584		580,685			594,857
Income from operations	10,991			64,353		65,745			41,485
Other (expense) income, net	(299		)	846		(996		)	(4,061		)
Net (loss) income (2)	(12,631		)	30,747		31,089			16,431
Basic (loss) earnings per share (3)	(0.22		)	0.55		0.55			0.29
Diluted (loss) earnings per share (3)	(0.22		)	0.54		0.55			0.29



	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
	(in thousands except per share amounts)
2017
Revenues	$	688,941		$	752,788		$	755,846		$	747,403
Cost of revenues (1)	496,585			519,803			519,595			526,690
Income from operations	5,433			46,744			47,663			27,935
Other expense, net	(1,549		)	(833		)	(432		)	(3,305		)
Net (loss) income (2)	(21,393		)	25,880			12,058			84,194
Basic (loss) earnings per share (3)	(0.37		)	0.45			0.21			1.48
Diluted (loss) earnings per share (3)	(0.37		)	0.45			0.21			1.48

______________________________________


(1)	Items shown separately on the statements of operations consist of (i) accretion of environmental liabilities and (ii) depreciation and amortization.

(2)

The second quarter of 2017 net income includes a $31.7 million pre-tax gain on the sale of a non-core line of business within the Company's Environmental Services segment and a $6.0 million loss on early extinguishment of debt. The third quarter of 2018 and 2017 net income had a $2.5 million and $1.9 million loss on early extinguishment of debt, respectively. As a result of the Tax Act, the fourth quarter of 2017 net income includes a $93.0 million tax benefit related to a reduction of the Company's net deferred tax liability.


(3)	(Loss) earnings per share are computed independently for each of the quarters presented. Accordingly, the quarterly basic and diluted (loss) earnings per share may not equal the total computed for the year.

SCHEDULE II VALUATION AND QUALIFYING ACCOUNTS

12 Months Ended

Dec. 31, 2018

SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]

SCHEDULE II VALUATION AND QUALIFYING ACCOUNTS

SCHEDULE II

VALUATION AND QUALIFYING ACCOUNTS

For the Three Years Ended December 31, 2018

(in thousands)



Allowance for Doubtful Accounts	Balance Beginning of Period		Additions Charged to Operating Expense		Deductions from Reserves(a)		Balance End of Period
2016	$	15,194	$	6,907	$	7,055	$	15,046
2017	$	15,046	$	7,901	$	6,774	$	16,173
2018	$	16,173	$	15,817	$	5,622	$	26,368

________________________________________


(a)	Amounts deemed uncollectible, net of recoveries.



Revenue Allowance(b)	Balance Beginning of Period		Additions Charged to Revenue		Deductions from Reserves		Balance End of Period
2016	$	16,232	$	24,252	$	26,281	$	14,203
2017	$	14,203	$	24,862	$	27,439	$	11,626
2018	$	11,626	$	41,338	$	35,017	$	17,947

________________________________________

(b)

Due to the nature of the Company's businesses and the invoices that result from the services provided, customers may withhold payments and attempt to renegotiate amounts invoiced. In addition, for some of the services provided, the Company's invoices are based on quotes that can either generate credits or debits when the actual revenue amount is known. Based on industry knowledge and historical trends, the Company records a revenue allowance accordingly. This practice causes the volume of activity flowing through the revenue allowance during the year to be higher than the balance at the end of the year. Increases in overall sales volumes and the expansion of the customer base in recent years have also increased the volume of additions and deductions to the allowance during the year. The revenue allowance is intended to cover the net amount of revenue adjustments that may need to be credited to customers' accounts in future periods. Management determines the appropriate total revenue allowance by evaluating the following factors on a customer-by-customer basis as well as on a consolidated level: trends in adjustments to previously billed amounts, existing economic conditions and other information as deemed applicable. Revenue allowance estimates can differ materially from the actual adjustments, but historically the revenue allowance has been sufficient to cover the net amount of the reserve adjustments issued in subsequent reporting periods.



Valuation Allowance on Deferred Tax Assets	Balance Beginning of Period		Additions Charged to Income Tax Expense		Other Changes to Reserves		Balance End of Period
2016	$	30,916	$	22,564	$	1,709	$	55,189
2017	$	55,189	$	9,052	$	4,114	$	68,355
2018	$	68,355	$	10,466	$	474	$	79,295

SIGNIFICANT ACCOUNTING POLICIES (Policies)

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

Principles of Consolidation

Use of Estimates

Cash, Cash Equivalents and Uncashed Checks

Marketable Securities

(2) SIGNIFICANT ACCOUNTING POLICIES (Continued)




	December 31, 2018		December 31, 2017
Commercial paper	$	8,126	$	2,048
Total cash equivalents	8,126		2,048

U.S. Treasury securities	10,133		3,855
Corporate notes and bonds	38,036		32,729
Commercial paper	4,687		1,595
Total short-term marketable securities	52,856		38,179
Total financial assets	$	60,982	$	40,227

Allowances for Doubtful Accounts

Credit Concentration

Inventories and Supplies

Property, Plant and Equipment (excluding landfill assets)

(2) SIGNIFICANT ACCOUNTING POLICIES (Continued)

The Company depreciates and amortizes the cost of these assets, using the straight-line method as follows:



Asset Classification		Estimated Useful Life
Buildings and building improvements
Buildings		20–42 years
Leasehold and building improvements		2–45 years
Camp and lodging equipment		8–15 years
Vehicles		2–15 years
Equipment
Capitalized software and computer equipment		3–5 years
Containers and railcars		8–16 years
All other equipment		4–30 years
Furniture and fixtures		5–8 years

Goodwill

Permits and other intangibles

Leases

(2) SIGNIFICANT ACCOUNTING POLICIES (Continued)

rent increases on a straight-line basis over the lease term beginning with the date the Company takes possession of the leased assets.

Landfill Accounting


•	Personnel are actively working to obtain the permit or permit modifications (land use, state, provincial and federal) necessary for expansion of an existing landfill, and progress is being made on the project.


•	Management expects to submit the application within the next year and to receive all necessary approvals to accept waste within the next 5 years.


•	At the time the expansion is included in the Company's estimate of the landfill's useful economic life, it is probable that the required approvals will be received within the normal application and processing time periods for approvals in the jurisdiction in which the landfill is located.


•	The Company or other owner of the landfill has a legal right to use or obtain the right to use the land associated with the expansion plan.


•	There are no significant known political, technical, legal or business restrictions or issues that could impair the success of such expansion.


•	A financial feasibility analysis has been completed and the results demonstrate that the expansion will have a positive financial and operational impact such that management is committed to pursuing the expansion.


•	Additional airspace and related additional costs, including permitting, final closure and post-closure costs, have been estimated based on the conceptual design of the proposed expansion.

(2) SIGNIFICANT ACCOUNTING POLICIES (Continued)

if the Company determines a landfill has more actual expansion airspace, amortization expense would decrease and profitability would increase.



		Remaining Lives (Years)	Remaining Highly Probable Airspace (cubic yards) (in thousands)
Facility Name	Location	Remaining Lives (Years)	Permitted	Unpermitted	Total
Altair	Texas	3	311	—	311
Buttonwillow	California	21	6,234	—	6,234
Deer Park	Texas	4	141	—	141
Deer Trail	Colorado	28	1,755	—	1,755
Grassy Mountain	Utah	51	194	4,830	5,024
Kimball	Nebraska	9	190	—	190
Lambton	Ontario	64	4,821	—	4,821
Lone Mountain	Oklahoma	18	4,124	—	4,124
Ryley	Alberta	7	906	—	906
Sawyer	North Dakota	87	3,522	—	3,522
Westmorland	California	64	2,732	—	2,732
			24,930	4,830	29,760

At December 31, 2018 and 2017, the Company had no cubic yards of permitted, but not highly probable, airspace.

The following table presents the remaining highly probable airspace from January 1, 2016 through December 31, 2018 (in thousands of cubic yards):



	2018		2017		2016
Remaining capacity at January 1,	31,113		32,228		29,786
Changes in highly probable airspace, net	(223	)	—		3,464
Consumed	(1,130	)	(1,115	)	(1,022	)
Remaining capacity at December 31,	29,760		31,113		32,228

(2) SIGNIFICANT ACCOUNTING POLICIES (Continued)

Non-Landfill Closure and Post-Closure Liabilities

Remedial Liabilities

(2) SIGNIFICANT ACCOUNTING POLICIES (Continued)


•	Remedial liabilities assumed relating to acquisitions are and will continue to be inflated using the inflation rates at the time of each acquisition (ranging from 1.01% to 2.57%) until the expected time of payment, then discounted at the risk-free interest rate at the time of such acquisition (ranging from 1.37% to 5.99%).


•	Remedial liabilities incurred subsequent to the acquisitions and remedial liabilities of the Company that existed prior to the acquisitions have been and will continue to be recorded at the estimated current value of the liabilities, which is usually neither increased for inflation nor reduced for discounting.

Foreign Currency

Advertising Expense

Advertising costs are expensed as incurred. Advertising expense was approximately $10.5 million in 2018, $11.8 million in 2017 and $10.8 million in 2016.

Stock-Based Compensation

Income Taxes

Earnings per Share

Earnings per Share ("EPS")

Recent Accounting Pronouncements

Standards implemented

(2) SIGNIFICANT ACCOUNTING POLICIES (Continued)

which resulted in a $1.4 million charge to other (expense) income, net for the change in fair value of equity securities purchased in 2018.

Standards to be implemented

The Company is evaluating the impact that the below standards to be implemented will have on the Company's consolidated financial statements.

SIGNIFICANT ACCOUNTING POLICIES (Tables)

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

Schedule of Cash Equivalents and Marketable Securities

As of December 31, 2018 and 2017 the Company has recorded total marketable securities and cash equivalents of $61.0 million and $40.2 million, respectively, as shown below (in thousands).

(2) SIGNIFICANT ACCOUNTING POLICIES (Continued)




	December 31, 2018		December 31, 2017
Commercial paper	$	8,126	$	2,048
Total cash equivalents	8,126		2,048

U.S. Treasury securities	10,133		3,855
Corporate notes and bonds	38,036		32,729
Commercial paper	4,687		1,595
Total short-term marketable securities	52,856		38,179
Total financial assets	$	60,982	$	40,227

Schedule of Asset Classification and Estimated Useful Life

The Company depreciates and amortizes the cost of these assets, using the straight-line method as follows:



Asset Classification		Estimated Useful Life
Buildings and building improvements
Buildings		20–42 years
Leasehold and building improvements		2–45 years
Camp and lodging equipment		8–15 years
Vehicles		2–15 years
Equipment
Capitalized software and computer equipment		3–5 years
Containers and railcars		8–16 years
All other equipment		4–30 years
Furniture and fixtures		5–8 years

Property, plant and equipment consisted of the following (in thousands):



	December 31, 2018		December 31, 2017
Land	$	123,734	$	121,658
Asset retirement costs (non-landfill)	15,148		14,593
Landfill assets	154,918		144,539
Buildings and improvements	440,188		414,384
Camp and lodging equipment	152,998		170,012
Vehicles	721,735		617,959
Equipment	1,697,490		1,644,102
Furniture and fixtures	5,453		5,708
Construction in progress	20,931		57,618
	3,332,595		3,190,573
Less - accumulated depreciation and amortization	1,770,617		1,603,208
Total property, plant and equipment, net	$	1,561,978	$	1,587,365

Schedule of Active Landfill Sites



		Remaining Lives (Years)	Remaining Highly Probable Airspace (cubic yards) (in thousands)
Facility Name	Location	Remaining Lives (Years)	Permitted	Unpermitted	Total
Altair	Texas	3	311	—	311
Buttonwillow	California	21	6,234	—	6,234
Deer Park	Texas	4	141	—	141
Deer Trail	Colorado	28	1,755	—	1,755
Grassy Mountain	Utah	51	194	4,830	5,024
Kimball	Nebraska	9	190	—	190
Lambton	Ontario	64	4,821	—	4,821
Lone Mountain	Oklahoma	18	4,124	—	4,124
Ryley	Alberta	7	906	—	906
Sawyer	North Dakota	87	3,522	—	3,522
Westmorland	California	64	2,732	—	2,732
			24,930	4,830	29,760

Remaining Highly Probable Airspace

The following table presents the remaining highly probable airspace from January 1, 2016 through December 31, 2018 (in thousands of cubic yards):



	2018		2017		2016
Remaining capacity at January 1,	31,113		32,228		29,786
Changes in highly probable airspace, net	(223	)	—		3,464
Consumed	(1,130	)	(1,115	)	(1,022	)
Remaining capacity at December 31,	29,760		31,113		32,228

BUSINESS COMBINATIONS (Tables)

12 Months Ended

Dec. 31, 2018

Business Combinations [Abstract]

Summary of Allocation of Purchase Price

The allocation of the purchase price consists of the following amounts (in thousands):



	Final Allocation
Accounts receivable	$	16,242
Inventories and supplies	12,688
Prepaid expenses and other current assets	752
Property, plant and equipment	143,916
Permits and other intangibles	28,856
Current liabilities	(19,905		)
Closure and post-closure liabilities, less current portion	(3,004		)
Remedial liabilities, less current portion	(2,545		)
Deferred taxes, unrecognized tax benefits and other long-term liabilities	(20,219		)
Total identifiable net assets	156,781
Goodwill	47,977
Total purchase price, net of cash acquired	$	204,758

The components and preliminary allocation of the purchase price for the Veolia Business consist of the following amounts (in thousands):



	At Acquisition Date As Reported December 31, 2018
Accounts receivable, including unbilled receivable	$	38,201
Inventories and supplies	1,126
Prepaid expenses and other current assets	828
Property, plant and equipment	72,243
Permits and other intangibles	5,140
Current liabilities	(18,025		)
Closure and post-closure liabilities	(354		)
Total identifiable net assets	99,159
Goodwill	24,873
Total purchase price	$	124,032

REVENUES (Tables)

12 Months Ended

Dec. 31, 2018

Revenue from Contract with Customer [Abstract]

Disaggregation of Revenue

The following table presents the Company’s third party revenues disaggregated by revenue source (in thousands):



	For the Year Ended December 31, 2018
	Environmental Services		Safety-Kleen		Corporate		Total
Primary Geographical Markets
United States	$	1,598,402	$	1,196,661	$	1,082	$	2,796,145
Canada	405,441		98,694		23		504,158
Total third party revenues	$	2,003,843	$	1,295,355	$	1,105	$	3,300,303

Sources of Revenue (1)
Technical Services	$	1,037,388	$	—	$	—	$	1,037,388
Field and Emergency Response Services	304,727		—		—		304,727
Industrial Services	541,895		—		—		541,895
Oil, Gas and Lodging Services and Other	119,833		—		1,105		120,938
Safety-Kleen Environmental Services	—		795,077		—		795,077
Kleen Performance Products	—		500,278		—		500,278
Total third party revenues	$	2,003,843	$	1,295,355	$	1,105	$	3,300,303

_____________________


1.	All revenue except oil and oil product sales within Kleen Performance Products and product sales within Safety-Kleen Environmental Services, which include various automotive related fluids, shop supplies and direct blended oil sales, are recognized over time. Kleen Performance Products and Safety-Kleen Environmental Services product sales are recognized at a point in time.

Contract Balances



	December 31, 2018		December 31, 2017
Receivables	$	606,952	$	528,924
Contract Assets (Unbilled Receivables)	54,794		35,922
Contract Liabilities (Deferred Revenue)	61,843		67,822

DISPOSITION OF BUSINESS (Tables)

12 Months Ended

Dec. 31, 2018

Discontinued Operations and Disposal Groups [Abstract]

Disposition of Business

The following table presents income attributable to the Catalyst Services business included in the Company's consolidated results of operations for the period shown and through its disposition on September 1, 2016 (in thousands):



	For the year ended December 31,
	2016
Income before provision (benefit) for income taxes	$	290

The following table presents the carrying amounts of the Company's Transformer Services business that was disposed of on June 30, 2017 (in thousands):



	June 30, 2017
Total current assets	$	7,241
Property, plant and equipment, net	8,773
Total other assets	1,681
Total assets divested	17,695
Total current liabilities	3,849
Total other liabilities	1,170
Total liabilities divested	5,019
Net carrying value divested	$	12,676

The following table presents income attributable to the Transformer Services business included in the Company's consolidated results of operations for each of the periods shown and through its disposition on June 30, 2017 (in thousands):



	For the years ended December 31,
	2017		2016
Income before provision (benefit) for income taxes	$	2,771	$	4,187

The following table presents the carrying amounts of the Company's Catalyst Services business immediately preceding the disposition on September 1, 2016 (in thousands):



	September 1, 2016
Total current assets	$	19,019
Property, plant and equipment, net	11,154
Total other assets	6,500
Total assets divested	36,673
Total current liabilities	4,040
Total other liabilities	566
Total liabilities divested	4,606
Net carrying value divested	$	32,067

- Definition

Tabular disclosure of information related to a disposal group. Includes, but is not limited to, a discontinued operation, disposal classified as held-for-sale or disposed of by means other than sale or disposal of an individually significant component.

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+ Details

INVENTORIES AND SUPPLIES (Tables)

12 Months Ended

Dec. 31, 2018

Inventory Disclosure [Abstract]

Schedule of Inventory

Inventories and supplies consisted of the following (in thousands):



	December 31, 2018		December 31, 2017
Oil and oil related products	$	70,823	$	58,142
Supplies and drums	104,609		94,242
Solvent and solutions	10,657		9,167
Modular camp accommodations	—		1,826
Other	13,390		12,635
Total inventories and supplies	$	199,479	$	176,012

PROPERTY, PLANT, AND EQUIPMENT (Tables)

12 Months Ended

Dec. 31, 2018

Property, Plant and Equipment [Abstract]

Property, Plant and Equipment

The Company depreciates and amortizes the cost of these assets, using the straight-line method as follows:



Asset Classification		Estimated Useful Life
Buildings and building improvements
Buildings		20–42 years
Leasehold and building improvements		2–45 years
Camp and lodging equipment		8–15 years
Vehicles		2–15 years
Equipment
Capitalized software and computer equipment		3–5 years
Containers and railcars		8–16 years
All other equipment		4–30 years
Furniture and fixtures		5–8 years

Property, plant and equipment consisted of the following (in thousands):



	December 31, 2018		December 31, 2017
Land	$	123,734	$	121,658
Asset retirement costs (non-landfill)	15,148		14,593
Landfill assets	154,918		144,539
Buildings and improvements	440,188		414,384
Camp and lodging equipment	152,998		170,012
Vehicles	721,735		617,959
Equipment	1,697,490		1,644,102
Furniture and fixtures	5,453		5,708
Construction in progress	20,931		57,618
	3,332,595		3,190,573
Less - accumulated depreciation and amortization	1,770,617		1,603,208
Total property, plant and equipment, net	$	1,561,978	$	1,587,365

GOODWILL AND OTHER INTANGIBLE ASSETS (Tables)

12 Months Ended

Dec. 31, 2018

Goodwill and Intangible Assets Disclosure [Abstract]

Schedule of Changes to Goodwill

The changes in goodwill for the years ended December 31, 2018 and 2017 were as follows (in thousands):



	Environmental Services			Safety-Kleen			Totals
Balance at January 1, 2017	$	169,084		$	296,070		$	465,154
Increase from current period acquisitions	3,000			5,687			8,687
Measurement period adjustments from prior period acquisitions	—			2,186			2,186
Decrease from disposition of business	(1,300		)	—			(1,300		)
Foreign currency translation	1,602			2,194			3,796
Balance at December 31, 2017	$	172,386		$	306,137		$	478,523
Increase from current period acquisitions	37,007			3,697			40,704
Measurement period adjustments from prior period acquisitions	(78		)	—			(78		)
Foreign currency translation	(2,296		)	(2,664		)	(4,960		)
Balance at December 31, 2018	$	207,019		$	307,170		$	514,189

Schedule of Finite-Lived Intangible Assets by Major Class

As of December 31, 2018 and 2017, the Company's finite-lived and indefinite-lived intangible assets consisted of the following (in thousands):



	December 31, 2018						December 31, 2017
	Cost		Accumulated Amortization		Net		Cost		Accumulated Amortization		Net
Permits	$	177,583	$	79,358	$	98,225	$	174,721	$	74,347	$	100,374
Customer and supplier relationships	393,487		179,824		213,663		399,224		158,972		240,252
Other intangible assets	37,262		29,743		7,519		36,766		31,592		5,174
Total amortizable permits and other intangible assets	608,332		288,925		319,407		610,711		264,911		345,800
Trademarks and trade names	122,468		—		122,468		123,328		—		123,328
Total permits and other intangible assets	$	730,800	$	288,925	$	441,875	$	734,039	$	264,911	$	469,128

Schedule of Indefinite-Lived Intangible Assets

As of December 31, 2018 and 2017, the Company's finite-lived and indefinite-lived intangible assets consisted of the following (in thousands):



	December 31, 2018						December 31, 2017
	Cost		Accumulated Amortization		Net		Cost		Accumulated Amortization		Net
Permits	$	177,583	$	79,358	$	98,225	$	174,721	$	74,347	$	100,374
Customer and supplier relationships	393,487		179,824		213,663		399,224		158,972		240,252
Other intangible assets	37,262		29,743		7,519		36,766		31,592		5,174
Total amortizable permits and other intangible assets	608,332		288,925		319,407		610,711		264,911		345,800
Trademarks and trade names	122,468		—		122,468		123,328		—		123,328
Total permits and other intangible assets	$	730,800	$	288,925	$	441,875	$	734,039	$	264,911	$	469,128

Schedule of Expected Amortization for the Net Carrying Amount of Finite Lived Intangible Assets

The expected amortization of the net carrying amount of finite-lived intangible assets at December 31, 2018 is as follows (in thousands):



Years Ending December 31,	Expected Amortization
2019	$	33,091
2020	30,195
2021	27,553
2022	27,386
2023	23,468
Thereafter	177,714
	$	319,407

CLOSURE AND POST-CLOSURE LIABILITIES (Tables)

12 Months Ended

Dec. 31, 2018

Asset Retirement Obligation Disclosure [Abstract]

Schedule of Closure and Post-Closure Liabilities

The changes to closure and post-closure liabilities (also referred to as "asset retirement obligations") from January 1, 2017 through December 31, 2018 were as follows (in thousands):



	Landfill Retirement Liability			Non-Landfill Retirement Liability			Total
Balance at January 1, 2017	$	30,630		$	27,701		$	58,331
Liabilities assumed in acquisitions	—			59			59
Measurement period adjustments from prior period acquisitions	—			596			596
New asset retirement obligations	1,881			—			1,881
Adjustment related to disposition of business	—			(1,170		)	(1,170		)
Accretion	2,243			2,505			4,748
Changes in estimates recorded to statement of operations	(131		)	(109		)	(240		)
Changes in estimates recorded to balance sheet	364			(591		)	(227		)
Expenditures	(2,777		)	(448		)	(3,225		)
Currency translation and other	172			112			284
Balance at December 31, 2017	32,382			28,655			61,037
Liabilities assumed in acquisitions	—			685			685
New asset retirement obligations	2,518			—			2,518
Accretion	2,537			2,567			5,104
Changes in estimates recorded to statement of operations	(37		)	1,497			1,460
Changes in estimates recorded to balance sheet	1,867			64			1,931
Expenditures	(1,224		)	(1,057		)	(2,281		)
Currency translation and other	(234		)	(289		)	(523		)
Balance at December 31, 2018	$	37,809		$	32,122		$	69,931

Schedule of Expected Payments Related to Asset Retirement Obligations



Year ending December 31,
2019	$	10,574
2020	9,424
2021	10,941
2022	7,626
2023	9,264
Thereafter	271,314
Undiscounted closure and post-closure liabilities	319,143
Less: Discount at credit-adjusted risk-free rate	(155,999		)
Less: Undiscounted estimated closure and post-closure liabilities relating to airspace not yet consumed	(93,213		)
Present value of closure and post-closure liabilities	$	69,931

REMEDIAL LIABILITIES (Tables)

12 Months Ended

Dec. 31, 2018

Environmental Remediation Obligations [Abstract]

Changes to Remedial Liabilities

The changes to remedial liabilities from January 1, 2017 through December 31, 2018 were as follows (in thousands):



	Remedial Liabilities for Landfill Sites			Remedial Liabilities for Inactive Sites			Remedial Liabilities (Including Superfund) for Non-Landfill Operations			Total
Balance at January 1, 2017	$	1,777		$	64,151		$	62,079		$	128,007
Measurement period adjustments from prior period acquisitions	—			—			504			504
Accretion	86			2,648			1,978			4,712
Changes in estimates recorded to statement of operations	(21		)	(289		)	355			45
Expenditures	(42		)	(3,906		)	(5,792		)	(9,740		)
Currency translation and other	—			2,738			(1,798		)	940
Balance at December 31, 2017	1,800			65,342			57,326			124,468
Accretion	86			2,745			1,871			4,702
Changes in estimates recorded to statement of operations	(1		)	130			558			687
Expenditures	(47		)	(3,759		)	(4,028		)	(7,834		)
Currency translation and other	—			857			(1,863		)	(1,006		)
Balance at December 31, 2018	$	1,838		$	65,315		$	53,864		$	121,017

Remedial Liabilities Anticipated Payments for Each of the Next Five Years

Anticipated payments at December 31, 2018 (based on current estimated costs and anticipated timing of necessary regulatory approvals to commence work on remedial activities) for each of the next five years and thereafter were as follows (in thousands):



Year ending December 31,
2019	$	13,975
2020	15,467
2021	14,593
2022	9,560
2023	8,688
Thereafter	81,453
Undiscounted remedial liabilities	143,736
Less: Discount	(22,719		)
Total remedial liabilities	$	121,017

Environmental Exit Costs by Cost

Estimates Based on Type of Facility or Site (in thousands):



Type of Facility or Site	Remedial Liability		% of Total		Reasonably Possible Additional Liabilities(1)
Facilities now used in active conduct of the Company's business (41 facilities)	$	48,506	40.1	%	$	11,171
Inactive facilities not now used in active conduct of the Company's business but most of which were acquired because the assumption of remedial liabilities for such facilities was part of the purchase price for the CSD assets (35 facilities)	64,344		53.2		10,782
Superfund sites owned by third parties (17 sites)	8,167		6.7		817
Total	$	121,017	100.0	%	$	22,770

___________________________________


(1)	Amounts represent the high end of the range of management's best estimate of the reasonably possible additional liabilities.

(11) REMEDIAL LIABILITIES (Continued)

Estimates Based on Amount of Potential Liability (in thousands):



Location	Type of Facility or Site	Remedial Liability		% of Total		Reasonably Possible Additional Liabilities(1)
Baton Rouge, LA(2)	Closed incinerator and landfill	$	23,314	19.3	%	$	3,963
Bridgeport, NJ	Closed incinerator	18,616		15.4		2,577
Mercier, Quebec(2)	Idled incinerator and legal proceedings	9,809		8.1		1,037
Linden, NJ	Operating solvent recycling center	7,487		6.2		790
Various(2)	All other incinerators, landfills, wastewater treatment facilities and service centers (72 facilities)	53,624		44.3		13,586
Various(2)	Superfund sites (each representing less than 5% of total liabilities) owned by third parties (17 sites)	8,167		6.7		817
Total		$	121,017	100.0	%	$	22,770

_________________________________


(1)	Amounts represent the high end of the range of management's best estimate of the reasonably possible additional liabilities.


(2)	$17.9 million of the $121.0 million remedial liabilities and $1.8 million of the $22.8 million reasonably possible additional liabilities include estimates of remediation liabilities related to the legal and administrative proceedings discussed in Note 18, "Commitments and Contingencies," as well as other such estimated remedial liabilities.

FINANCING ARRANGEMENTS (Tables)

12 Months Ended

Dec. 31, 2018

Debt Disclosure [Abstract]

Summary of Financing Arrangements

The following table is a summary of the Company's financing arrangements (in thousands):



Current Obligations:	December 31, 2018			December 31, 2017
Senior secured Term Loan Agreement ("Term Loan Agreement")	$	7,535		$	4,000

Long-Term Obligations:
Senior secured Term Loan Agreement due June 30, 2024	$	734,697		$	394,000
Senior unsecured notes, at 5.25%, due August 1, 2020 ("2020 Notes")	—			400,000
Senior unsecured notes, at 5.125%, due June 1, 2021 ("2021 Notes")	845,000			845,000
Long-term obligations, at par	$	1,579,697		$	1,639,000
Unamortized debt issuance costs and premium, net	$	(14,676	)	$	(13,463	)
Long-term obligations, at carrying value	$	1,565,021		$	1,625,537

- Definition

Tabular disclosure of long-debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the entity, if longer.

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+ Details

INCOME TAXES (Tables)

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Schedule of Income before Income Tax, Domestic and Foreign

The domestic and foreign components of income before provision (benefit) for income taxes were as follows (in thousands):



	For the Year Ended December 31,
	2018			2017			2016
Domestic	$	115,070		$	101,714		$	87,328
Foreign	(20,588		)	(43,025		)	(78,612		)
Total	$	94,482		$	58,689		$	8,716

Schedule of Components of Provision for Income Taxes

The provision (benefit) for income taxes consisted of the following (in thousands):



	For the Year Ended December 31,
	2018			2017			2016
Current:
Federal	$	(7,677	)	$	25,613		$	14,798
State	12,653			11,083			8,763
Foreign	4,781			4,589			9,844
	9,757			41,285			33,405
Deferred
Federal	19,899			(85,488		)	21,814
State	(1,205		)	1,085			1,644
Foreign	395			1,068			(8,274		)
	19,089			(83,335		)	15,184
Provision (benefit) for income taxes	$	28,846		$	(42,050	)	$	48,589

Schedule of Effective Income Tax Rate Reconciliation

The effective income tax rate varied from the amount computed using the statutory federal income tax rate as follows (in thousands):



	For the Year Ended December 31,
	2018			2017			2016
Tax expense at US statutory rate	$	19,841		$	20,541		$	3,051
State income taxes, net of federal benefit	8,711			4,547			6,010
Foreign rate differential	(1,124		)	3,733			3,646
Valuation allowance	10,466			16,552			22,564
Uncertain tax position interest and penalties	(1,806		)	3,730			107
Goodwill impairment	—			—			11,905
Tax credits	(9,799		)	—			—
Other	2,845			1,856			1,306
Adjustment for Tax Cuts and Jobs Act	(288		)	(93,009		)	—
Provision (benefit) for income taxes	$	28,846		$	(42,050	)	$	48,589

Schedule of Deferred Tax Assets and Liabilities

The components of the total net deferred tax assets and liabilities at December 31, 2018 and 2017 were as follows (in thousands):



	2018			2017
Deferred tax assets:
Provision for doubtful accounts	$	10,715		$	7,417
Closure, post-closure and remedial liabilities	28,380			28,189
Accrued expenses	15,686			15,382
Accrued compensation	7,774			1,903
Net operating loss carryforwards(1)	43,284			46,650
Tax credit carryforwards(2)	16,909			17,504
Uncertain tax positions accrued interest and federal benefit	519			921
Stock-based compensation	3,440			2,268
Other	7,067			3,258
Total deferred tax assets	133,774			123,492
Deferred tax liabilities:
Property, plant and equipment	(164,246		)	(144,325		)
Permits and other intangible assets	(103,539		)	(107,407		)
Prepaids	(9,187		)	(8,080		)
Total deferred tax liabilities	(276,972		)	(259,812		)
Total net deferred tax liability before valuation allowance	(143,198		)	(136,320		)
Less valuation allowance	(79,295		)	(68,355		)
Net deferred tax liabilities	$	(222,493	)	$	(204,675	)

___________________________________


(1)	As of December 31, 2018, the net operating loss carryforwards included (i) state net operating loss carryovers of $185.1 million which will begin to expire in 2019, (ii) federal net operating loss carryforwards of $49.8 million which will begin to expire in 2025, and (iii) foreign net operating loss carryforwards of $103.3 million which will begin to expire in 2019.


(2)	As of December 31, 2018, the foreign tax credit carryforwards of $16.5 million will expire between 2020 and 2024.

Summary of Income Tax Contingencies

The changes to unrecognized tax benefits (excluding related penalties and interest) from January 1, 2016 through December 31, 2018, were as follows (in thousands):



	2018			2017			2016
Unrecognized tax benefits as of January 1	$	5,121		$	1,738		$	2,064
Additions to current year tax positions	—			1,457			—
(Reductions) additions to prior year tax positions	(625		)	2,031			—
Expirations	(1,115		)	(231		)	(533		)
Foreign currency translation	(222		)	126			207
Unrecognized tax benefits as of December 31	$	3,159		$	5,121		$	1,738

ACCUMULATED OTHER COMPREHENSIVE LOSS (Tables)

12 Months Ended

Dec. 31, 2018

Equity [Abstract]

Schedule of Reclassification of Accumulated Other Comprehensive Income (Loss)

The changes in accumulated other comprehensive loss by component and related tax effects for the years ended December 31, 2018, 2017 and 2016 were as follows (in thousands):



	Foreign Currency Translation Adjustments			Unrealized (Losses) Gains on Available-for-Sale Securities			Unrealized Loss on Interest Rate Hedge			Unfunded Pension Liability			Total
Balance at January 1, 2016	$	(252,939	)	$	—		$	—		$	(1,953	)	$	(254,892	)
Other comprehensive income (loss) before reclassifications	23,967			(535		)	—			216			23,648
Amounts reclassified out of accumulated other comprehensive loss	—			—			—			—			—
Tax benefit (loss)	16,761			214			—			(57		)	16,918
Other comprehensive income (loss)	40,728			(321		)	—			159			40,566
Balance at December 31, 2016	(212,211		)	(321		)	—			(1,794		)	(214,326		)
Other comprehensive income before reclassifications	41,636			184			—			146			41,966
Amounts reclassified out of accumulated other comprehensive loss	—			222			—			—			222
Tax loss	—			(231		)	—			(38		)	(269		)
Other comprehensive income	41,636			175			—			108			41,919
Balance at December 31, 2017	(170,575		)	(146		)	—			(1,686		)	(172,407		)
Other comprehensive (loss) income before tax effects	(47,374		)	182			(9,579		)	124			(56,647		)
Amounts reclassified out of accumulated other comprehensive loss	—			—			806			—			806
Tax benefit (loss)	5,024			(105		)	—			(42		)	4,877
Other comprehensive (loss) income	(42,350		)	77			(8,773		)	82			(50,964		)
Balance at December 31, 2018	$	(212,925	)	$	(69	)	$	(8,773	)	$	(1,604	)	$	(223,371	)

Reclassification out of Accumulated Other Comprehensive Income



	For the years ended December 31,
Other Comprehensive Income Components	2018			2017			Location
Unrealized (losses) gains on available-for-sale securities	$	—		$	(222	)	Other (expense) income, net
Unrealized loss on interest rate hedge	(806		)	—			Interest expense, net of interest income

STOCK-BASED COMPENSATION AND EMPLOYEE BENEFIT PLANS (Tables)

12 Months Ended

Dec. 31, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Summary of Restricted Stock

The following table summarizes information about restricted stock awards for the year ended December 31, 2018:



Restricted Stock	Number of Shares		Weighted Average Grant-Date Fair Value
Unvested at January 1, 2018	604,933		$	54.23
Granted	327,466		55.02
Vested	(198,673	)	54.22
Forfeited	(76,486	)	54.00
Unvested at December 31, 2018	657,240		$	54.65

Schedule of Performance Stock Awards

The following table summarizes information about performance stock awards for the year ended December 31, 2018:



Performance Stock	Number of Shares		Weighted Average Grant-Date Fair Value
Unvested at January 1, 2018	190,129		$	55.63
Granted	171,584		55.71
Vested	(21,416	)	54.82
Forfeited	(126,807	)	53.59
Unvested at December 31, 2018	213,490		$	55.71

COMMITMENTS AND CONTINGENCIES (Tables)

12 Months Ended

Dec. 31, 2018

Commitments and Contingencies Disclosure [Abstract]

Schedule of Future Minimum Lease Payments for Operating Leases

The following is a summary of future minimum payments under operating leases that have initial or remaining non-cancelable lease terms in excess of one year at December 31, 2018 (in thousands):



Year	Total Operating Leases
2019	$	56,480
2020	45,467
2021	33,564
2022	24,509
2023	15,253
Thereafter	35,778
Total minimum lease payments	$	211,051

Self-Insurance Liabilities Anticipated Payments



Years ending December 31,
2019	$	20,171
2020	12,799
2021	7,964
2022	4,992
2023	4,082
Thereafter	6,385
Undiscounted self-insurance liabilities	56,393
Less: Discount	2,492
Total self-insurance liabilities (included in accrued expenses)	$	53,901

SEGMENT REPORTING (Tables)

12 Months Ended

Dec. 31, 2018

Segment Reporting [Abstract]

Reconciliation of Third Party Revenues to Direct Revenues

The following table reconciles third-party revenues to direct revenues for the years ended December 31, 2018, 2017 and 2016 (in thousands):



	For the Year Ended December 31, 2018
	Environmental Services		Safety-Kleen			Corporate Items			Totals
Third-party revenues	$	2,003,843	$	1,295,355		$	1,105		$	3,300,303
Intersegment revenues, net	134,104		(134,104		)	—			—
Corporate Items, net	3,247		31			(3,278		)	—
Direct revenues	$	2,141,194	$	1,161,282		$	(2,173	)	$	3,300,303



	For the Year Ended December 31, 2017
	Environmental Services		Safety-Kleen			Corporate Items			Totals
Third-party revenues	$	1,728,700	$	1,213,703		$	2,575		$	2,944,978
Intersegment revenues, net	125,822		(125,822		)	—			—
Corporate Items, net	2,952		5			(2,957		)	—
Direct revenues	$	1,857,474	$	1,087,886		$	(382	)	$	2,944,978



	For the Year Ended December 31, 2016
	Environmental Services		Safety-Kleen			Corporate Items			Totals
Third-party revenues	$	1,641,432	$	1,110,727		$	3,067		$	2,755,226
Intersegment revenues, net	115,013		(115,013		)	—			—
Corporate Items, net	2,388		369			(2,757		)	—
Direct revenues	$	1,758,833	$	996,083		$	310		$	2,755,226

Reconciliation to Consolidated Statements of Income to Adjusted EBITDA

The following table presents Adjusted EBITDA information used by management by reported segment (in thousands):



	For the Year Ended December 31,
	2018			2017			2016
Adjusted EBITDA:
Environmental Services	$	380,856		$	321,310		$	319,075
Safety-Kleen	282,029			249,811			219,546
Corporate Items	(171,880		)	(145,464		)	(138,267		)
Total	491,005			425,657			400,354
Reconciliation to Consolidated Statements of Operations:
Accretion of environmental liabilities	9,806			9,460			10,177
Depreciation and amortization	298,625			288,422			287,002
Goodwill impairment charge	—			—			34,013
Income from operations	182,574			127,775			69,162
Other expense (income), net	4,510			6,119			(6,195		)
Loss on early extinguishment of debt	2,488			7,891			—
Gain on sale of businesses	—			(30,732		)	(16,884		)
Interest expense, net of interest income	81,094			85,808			83,525
Income from operations before provision (benefit) for income taxes	$	94,482		$	58,689		$	8,716

Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas [Table Text Block]

For the years ended December 31, 2018, 2017, and 2016, the Company generated direct revenues in the following geographic locations (in thousands):



	For the Year Ended December 31,
	2018				2017				2016
	Revenue		% of Total		Revenue		% of Total		Revenue		% of Total
United States	$	2,721,814	82.5	%	$	2,392,000	81.2	%	$	2,213,355	80.3	%
Canada	578,489		17.5	%	552,978		18.8	%	541,871		19.7	%
Total Revenues	$	3,300,303	100.0	%	$	2,944,978	100.0	%	$	2,755,226	100.0	%



	For the Year Ended December 31,
	2018				2017
	Total		% of Total		Total		% of Total
Property, plant and equipment, net
United States	$	1,233,949	79.0	%	$	1,175,437	74.0	%
Canada	328,029		21.0	%	411,928		26.0	%
Total property, plant and equipment, net	$	1,561,978	100.0	%	$	1,587,365	100.0	%

Permits and other intangibles, net
United States	$	393,045	88.9	%	$	408,654	87.1	%
Canada	48,830		11.1	%	60,474		12.9	%
Total permits and other intangibles, net	$	441,875	100.0	%	$	469,128	100.0	%

PP&E and Intangible Assets by Segment

The following table presents assets by reported segment and in the aggregate (in thousands):



	December 31, 2018		December 31, 2017
Property, plant and equipment, net
Environmental Services	$	951,867	$	927,139
Safety-Kleen	553,220		582,162
Corporate Items	56,891		78,064
Total property, plant and equipment, net	$	1,561,978	$	1,587,365

Goodwill and Permits and other intangibles, net
Environmental Services
Goodwill	$	207,019	$	172,386
Permits and other intangibles, net	93,313		97,519
Total Environmental Services	300,332		269,905

Safety-Kleen
Goodwill	$	307,170	$	306,137
Permits and other intangibles, net	348,562		371,609
Total Safety-Kleen	655,732		677,746

Total	$	956,064	$	947,651

Total Assets by Segment

The following table presents the total assets by reported segment (in thousands):



	December 31, 2018		December 31, 2017
Environmental Services	$	1,640,706	$	1,541,241
Safety-Kleen	1,431,381		1,471,291
Corporate Items	666,234		694,038
Total	$	3,738,321	$	3,706,570

Total Assets by Geographical Area

The following table presents the total assets by geographical area (in thousands):



	December 31, 2018		December 31, 2017
United States	$	3,090,311	$	2,985,394
Canada	648,010		721,176
Total	$	3,738,321	$	3,706,570

GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Tables)

12 Months Ended

Dec. 31, 2018

Guarantor and Non-Guarantor Subsidiaries Financial Information [Abstract]

Schedule of Condensed Consolidating Balance Sheet

Following is the condensed consolidating balance sheet at December 31, 2018 (in thousands):



	Clean Harbors, Inc.		Guarantor Subsidiaries		Non-Guarantor Subsidiaries		Consolidating Adjustments			Total
Assets:
Cash and cash equivalents	$	27,308	$	101,302	$	97,897	$	—		$	226,507
Short-term marketable securities	67		—		52,789		—			52,856
Intercompany receivables	262,475		721,521		60,693		(1,044,689		)	—
Accounts receivable, net	—		520,785		86,167		—			606,952
Other current assets	—		289,869		49,631		(23,657		)	315,843
Property, plant and equipment, net	—		1,233,578		328,400		—			1,561,978
Investments in subsidiaries	3,162,704		571,304		—		(3,734,008		)	—
Intercompany debt receivable	—		14,669		21,000		(35,669		)	—
Goodwill	—		456,307		57,882		—			514,189
Permits and other intangibles, net	—		393,045		48,830		—			441,875
Other long-term assets	1,551		13,545		3,025		—			18,121
Total assets	$	3,454,105	$	4,315,925	$	806,314	$	(4,838,023	)	$	3,738,321
Liabilities and Stockholders' Equity:
Current liabilities	$	20,170	$	457,164	$	148,601	$	(23,657	)	$	602,278
Intercompany payables	699,158		321,846		23,685		(1,044,689		)	—
Closure, post-closure and remedial liabilities, net	—		151,480		16,434		—			167,914
Long-term obligations	1,565,021		—		—		—			1,565,021
Intercompany debt payable	—		21,000		14,669		(35,669		)	—
Other long-term liabilities	—		212,924		20,428		—			233,352
Total liabilities	2,284,349		1,164,414		223,817		(1,104,015		)	2,568,565
Stockholders' equity	1,169,756		3,151,511		582,497		(3,734,008		)	1,169,756
Total liabilities and stockholders' equity	$	3,454,105	$	4,315,925	$	806,314	$	(4,838,023	)	$	3,738,321

(20) GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Continued)

Following is the condensed consolidating balance sheet at December 31, 2017 (in thousands):



	Clean Harbors, Inc.		Guarantor Subsidiaries		Non-Guarantor Subsidiaries		Consolidating Adjustments			Total
Assets:
Cash and cash equivalents	$	51,638	$	207,777	$	59,984	$	—		$	319,399
Short-term marketable securities	—		—		38,179		—			38,179
Intercompany receivables	238,339		590,100		52,909		(881,348		)	—
Accounts receivable, net	—		433,042		95,882		—			528,924
Other current assets	897		233,602		52,947		(19,892		)	267,554
Property, plant and equipment, net	—		1,174,975		412,390		—			1,587,365
Investments in subsidiaries	3,112,547		569,568		—		(3,682,115		)	—
Intercompany debt receivable	—		92,530		21,000		(113,530		)	—
Goodwill	—		415,641		62,882		—			478,523
Permits and other intangibles, net	—		408,655		60,473		—			469,128
Other long-term assets	2,084		12,064		3,350		—			17,498
Total assets	$	3,405,505	$	4,137,954	$	859,996	$	(4,696,885	)	$	3,706,570
Liabilities and Stockholders' Equity:
Current liabilities	$	16,954	$	371,135	$	135,620	$	(19,892	)	$	503,817
Intercompany payables	574,812		289,531		17,005		(881,348		)	—
Closure, post-closure and remedial liabilities, net	—		148,872		16,851		—			165,723
Long-term obligations	1,625,537		—		—		—			1,625,537
Intercompany debt payable	—		21,000		92,530		(113,530		)	—
Other long-term liabilities	—		201,086		22,205		—			223,291
Total liabilities	2,217,303		1,031,624		284,211		(1,014,770		)	2,518,368
Stockholders' equity	1,188,202		3,106,330		575,785		(3,682,115		)	1,188,202
Total liabilities and stockholders' equity	$	3,405,505	$	4,137,954	$	859,996	$	(4,696,885	)	$	3,706,570

Schedule of Consolidating Statement of Income

Following is the consolidating statement of operations for the year ended December 31, 2018 (in thousands):



	Clean Harbors, Inc.			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating Adjustments			Total
Revenues
Service revenues	$	—		$	2,145,310		$	621,435		$	(57,506	)	$	2,709,239
Product revenues	—			537,400			66,210			(12,546		)	591,064
Total revenues	—			2,682,710			687,645			(70,052		)	3,300,303
Cost of revenues (exclusive of items shown separately below)
Service cost of revenues	—			1,421,693			497,788			(57,506		)	1,861,975
Product cost of revenues	—			419,377			36,745			(12,546		)	443,576
Total cost of revenues	—			1,841,070			534,533			(70,052		)	2,305,551
Selling, general and administrative expenses	347			419,984			83,416			—			503,747
Accretion of environmental liabilities	—			8,797			1,009			—			9,806
Depreciation and amortization	—			219,530			79,095			—			298,625
(Loss) income from operations	(347		)	193,329			(10,408		)	—			182,574
Other expense, net	(1,384		)	(1,284		)	(1,842		)	—			(4,510		)
Loss on early extinguishment of debt	(2,488		)	—			—			—			(2,488		)
Interest (expense) income, net	(83,362		)	1,252			1,016			—			(81,094		)
Equity in earnings of subsidiaries, net of tax	129,082			(25,765		)	—			(103,317		)	—
Intercompany interest income (expense)	—			2,841			(2,841		)	—			—
Income (loss) before (benefit) provision for income taxes	41,501			170,373			(14,075		)	(103,317		)	94,482
(Benefit) provision for income taxes	(24,135		)	46,267			6,714			—			28,846
Net income (loss)	65,636			124,106			(20,789		)	(103,317		)	65,636
Other comprehensive loss	(50,964		)	(50,964		)	(44,292		)	95,256			(50,964		)
Comprehensive income (loss)	$	14,672		$	73,142		$	(65,081	)	$	(8,061	)	$	14,672

(20) GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Continued)

Following is the consolidating statement of operations for the year ended December 31, 2017 (in thousands):



	Clean Harbors, Inc.			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating Adjustments			Total
Revenues
Service revenues	$	—		$	1,870,256		$	582,042		$	(53,648	)	$	2,398,650
Product revenues	—			492,036			66,511			(12,219		)	546,328
Total revenues	—			2,362,292			648,553			(65,867		)	2,944,978
Cost of revenues (exclusive of items shown separately below)
Service cost of revenues	—			1,224,326			471,120			(53,648		)	1,641,798
Product cost of revenues	—			386,455			46,639			(12,219		)	420,875
Total cost of revenues	—			1,610,781			517,759			(65,867		)	2,062,673
Selling, general and administrative expenses	—			373,050			83,598			—			456,648
Accretion of environmental liabilities	—			8,479			981			—			9,460
Depreciation and amortization	—			205,034			83,388			—			288,422
Income (loss) from operations	—			164,948			(37,173		)	—			127,775
Other expense, net	(222		)	(5,156		)	(741		)	—			(6,119		)
Loss on early extinguishment of debt	(7,891		)	—			—			—			(7,891		)
Gain on sale of business	—			30,732			—			—			30,732
Interest (expense) income, net	(87,113		)	1,523			(218		)	—			(85,808		)
Equity in earnings of subsidiaries, net of tax	157,963			(48,683		)	—			(109,280		)	—
Intercompany interest income (expense)	—			5,288			(5,288		)	—			—
Income (loss) before (benefit) provision for income taxes	62,737			148,652			(43,420		)	(109,280		)	58,689
(Benefit) provision for income taxes	(38,002		)	(10,117		)	6,069			—			(42,050		)
Net income (loss)	100,739			158,769			(49,489		)	(109,280		)	100,739
Other comprehensive income	41,919			41,919			38,131			(80,050		)	41,919
Comprehensive income (loss)	$	142,658		$	200,688		$	(11,358	)	$	(189,330	)	$	142,658

20) GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Continued)

Following is the consolidating statement of operations for the year ended December 31, 2016 (in thousands):



	Clean Harbors, Inc.			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating Adjustments			Total
Revenues
Service revenues	$	—		$	1,747,985		$	582,075		$	(49,251	)	$	2,280,809
Product revenues	—			410,868			73,793			(10,244		)	474,417
Total revenues	—			2,158,853			655,868			(59,495		)	2,755,226
Cost of revenues (exclusive of items shown separately below)
Service cost of revenues	—			1,116,132			476,329			(49,251		)	1,543,210
Product cost of revenues	—			349,069			50,822			(10,244		)	389,647
Total cost of revenues	—			1,465,201			527,151			(59,495		)	1,932,857
Selling, general and administrative expenses	85			341,963			79,967			—			422,015
Accretion of environmental liabilities	—			9,261			916			—			10,177
Depreciation and amortization	—			201,153			85,849			—			287,002
Goodwill impairment charge	—			—			34,013			—			34,013
(Loss) income from operations	(85		)	141,275			(72,028		)	—			69,162
Other income (expense), net	—			7,713			(1,518		)	—			6,195
Gain on sale of business	—			1,704			15,180			—			16,884
Interest (expense) income, net	(88,984		)	5,391			68			—			(83,525		)
Equity in earnings of subsidiaries, net of tax	13,568			(80,244		)	—			66,676			—
Intercompany interest income (expense)	—			19,855			(19,855		)	—			—
(Loss) income before (benefit) provision for income taxes	(75,501		)	95,694			(78,153		)	66,676			8,716
(Benefit) provision for income taxes	(35,628		)	82,643			1,574			—			48,589
Net (loss) income	(39,873		)	13,051			(79,727		)	66,676			(39,873		)
Other comprehensive income	40,566			40,566			15,291			(55,857		)	40,566
Comprehensive income (loss)	$	693		$	53,617		$	(64,436	)	$	10,819		$	693

Schedule of Condensed Consolidating Statement of Cash Flows

Following is the condensed consolidating statement of cash flows for the year ended December 31, 2018 (in thousands):



	Clean Harbors, Inc.			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating Adjustments			Total
Net cash from operating activities	$	34,135		$	260,101		$	78,974		$	—		$	373,210
Cash flows used in investing activities:
Additions to property, plant and equipment	—			(161,342		)	(32,002		)	—			(193,344		)
Proceeds from sale and disposal of fixed assets	—			4,174			11,271			—			15,445
Proceeds from sale of available-for-sale securities	—			—			28,723			—			28,723
Acquisitions, net of cash acquired	—			(151,023		)	—			—			(151,023		)
Additions to intangible assets, including costs to obtain or renew permits	—			(4,326		)	(362		)	—			(4,688		)
Purchases of available-for-sale securities	(1,450		)	—			(43,322		)	—			(44,772		)
Intercompany	—			(54,114		)	—			54,114			—
Net cash used in investing activities	(1,450		)	(366,631		)	(35,692		)	54,114			(349,659		)
Cash flows (used in) from financing activities:
Change in uncashed checks	—			55			77			—			132
Tax payments related to withholdings on vested restricted stock	(3,266		)	—			—			—			(3,266		)
Deferred financing costs paid	(4,027		)	—			—			—			(4,027		)
Repurchases of common stock	(45,080		)	—			—			—			(45,080		)
Principal payments on debt	(405,768		)	—			—			—			(405,768		)
Premium paid on early extinguishment of debt	(1,238		)	—			—			—			(1,238		)
Issuance of senior secured notes, net of discount	348,250			—			—			—			348,250
Borrowing from revolving credit facility	50,000			—			—			—			50,000
Payment on revolving credit facility	(50,000		)	—			—			—			(50,000		)
Intercompany	54,114			—			—			(54,114		)	—
Net cash (used in) from financing activities	(57,015		)	55			77			(54,114		)	(110,997		)
Effect of exchange rate change on cash	—			—			(5,446		)	—			(5,446		)
(Decrease) increase in cash and cash equivalents	(24,330		)	(106,475		)	37,913			—			(92,892		)
Cash and cash equivalents, beginning of year	51,638			207,777			59,984			—			319,399
Cash and cash equivalents, end of year	$	27,308		$	101,302		$	97,897		$	—		$	226,507

(20) GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Continued)

Following is the condensed consolidating statement of cash flows for the year ended December 31, 2017 (in thousands):



	Clean Harbors, Inc.			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating Adjustments			Total
Net cash from operating activities	$	16,292		$	217,001		$	52,405		$	—		$	285,698
Cash flows from (used in) investing activities:
Additions to property, plant and equipment	—			(142,211		)	(24,796		)	—			(167,007		)
Proceeds from sale and disposal of fixed assets	—			1,979			5,145			—			7,124
Proceeds from sale of available-for-sale securities	376			—			—			—			376
Proceeds from sale of business, net of transactional costs	—			45,245			181			—			45,426
Acquisitions, net of cash acquired	—			(11,427		)	(37,800		)	—			(49,227		)
Additions to intangible assets, including costs to obtain or renew permits	—			(1,153		)	(464		)	—			(1,617		)
Purchases of available-for-sale securities	—			—			(38,342		)	—			(38,342		)
Intercompany	—			(54,074		)	—			54,074			—
Intercompany debt	—			—			3,701			(3,701		)	—
Net cash from (used in) investing activities	376			(161,641		)	(92,375		)	50,373			(203,267		)
Cash flows used in financing activities:
Change in uncashed checks	—			(3,526		)	(2,414		)	—			(5,940		)
Proceeds from exercise of stock options	46			—			—			—			46
Tax payments related to withholdings on vested restricted stock	(3,149		)	—			—			—			(3,149		)
Deferred financing costs paid	(5,718		)	—			—			—			(5,718		)
Repurchases of common stock	(48,971		)	—			—			—			(48,971		)
Principal payments on debt	(402,000		)	—			—			—			(402,000		)
Premium paid on early extinguishment of debt	(6,028		)	—			—			—			(6,028		)
Issuance of senior secured notes, net of discount	399,000			—			—			—			399,000
Intercompany	54,074			—			—			(54,074		)	—
Intercompany debt	(3,701		)	—			—			3,701			—
Net cash used in financing activities	(16,447		)	(3,526		)	(2,414		)	(50,373		)	(72,760		)
Effect of exchange rate change on cash	—			—			2,731			—			2,731
Increase (decrease) in cash and cash equivalents	221			51,834			(39,653		)	—			12,402
Cash and cash equivalents, beginning of year	51,417			155,943			99,637			—			306,997
Cash and cash equivalents, end of year	$	51,638		$	207,777		$	59,984		$	—		$	319,399

(20) GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Continued)

Following is the condensed consolidating statement of cash flows for the year ended December 31, 2016 (in thousands):



	Clean Harbors, Inc.			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating Adjustments			Total
Net cash from operating activities	$	51,033		$	125,591		$	83,000		$	—		$	259,624
Cash flows used in investing activities:
Additions to property, plant and equipment	—			(194,184		)	(25,200		)	—			(219,384		)
Proceeds from sale and disposal of fixed assets	—			12,926			7,891			—			20,817
Proceeds on sale of business, net of transactional costs	—			18,885			28,249			—			47,134
Acquisitions, net of cash acquired	—			(196,915		)	(10,000		)	—			(206,915		)
Additions to intangible assets including costs to obtain or renew permits	—			(1,749		)	(1,082		)	—			(2,831		)
Purchases of available-for-sale securities	(102		)	—			(496		)	—			(598		)
Intercompany	—			(23,182		)	—			23,182			—
Intercompany debt	—			63,118			(21,000		)	(42,118		)	—
Investment in subsidiaries	(257,125		)	—			—			257,125			—
Net cash used in investing activities	(257,227		)	(321,101		)	(21,638		)	238,189			(361,777		)
Cash flows from (used in) financing activities:
Change in uncashed checks	—			(3,651		)	474			—			(3,177		)
Proceeds from exercise of stock options	627			—			—			—			627
Tax payments related to withholdings on vested restricted stock	(2,819		)	—			—			—			(2,819		)
Deferred financing costs paid	(4,031		)	—			—			—			(4,031		)
Repurchases of common stock	(22,188		)	—			—			—			(22,188		)
Excess tax benefit of stock-based compensation	1,198			—			—			—			1,198
Issuance of senior unsecured notes, including premium	250,625			250,625			—			(250,625		)	250,625
Intercompany	23,182			—			6,500			(29,682		)	—
Intercompany debt	—			21,000			(63,118		)	42,118			—
Net cash from (used in) financing activities	246,594			267,974			(56,144		)	(238,189		)	220,235
Effect of exchange rate change on cash	—			—			4,207			—			4,207
Increase in cash and cash equivalents	40,400			72,464			9,425			—			122,289
Cash and cash equivalents, beginning of year	11,017			83,479			90,212			—			184,708
Cash and cash equivalents, end of year	$	51,417		$	155,943		$	99,637		$	—		$	306,997

QUARTERLY DATA (UNAUDITED) (Tables)

12 Months Ended

Dec. 31, 2018

Quarterly Financial Information Disclosure [Abstract]

Quarterly Data (Unaudited)



	First Quarter			Second Quarter		Third Quarter			Fourth Quarter
	(in thousands except per share amounts)
2018
Revenues	$	749,778		$	849,140	$	843,181		$	858,204
Cost of revenues (1)	546,425			583,584		580,685			594,857
Income from operations	10,991			64,353		65,745			41,485
Other (expense) income, net	(299		)	846		(996		)	(4,061		)
Net (loss) income (2)	(12,631		)	30,747		31,089			16,431
Basic (loss) earnings per share (3)	(0.22		)	0.55		0.55			0.29
Diluted (loss) earnings per share (3)	(0.22		)	0.54		0.55			0.29



	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
	(in thousands except per share amounts)
2017
Revenues	$	688,941		$	752,788		$	755,846		$	747,403
Cost of revenues (1)	496,585			519,803			519,595			526,690
Income from operations	5,433			46,744			47,663			27,935
Other expense, net	(1,549		)	(833		)	(432		)	(3,305		)
Net (loss) income (2)	(21,393		)	25,880			12,058			84,194
Basic (loss) earnings per share (3)	(0.37		)	0.45			0.21			1.48
Diluted (loss) earnings per share (3)	(0.37		)	0.45			0.21			1.48

______________________________________


(1)	Items shown separately on the statements of operations consist of (i) accretion of environmental liabilities and (ii) depreciation and amortization.

(2)


(3)	(Loss) earnings per share are computed independently for each of the quarters presented. Accordingly, the quarterly basic and diluted (loss) earnings per share may not equal the total computed for the year.

SIGNIFICANT ACCOUNTING POLICIES (Marketable Securities and Cash Equivalents) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Marketable Securities [Line Items]
Total cash equivalents	$ 8,126	$ 2,048
Short-term marketable securities	52,856	38,179
Total financial assets	60,982	40,227
U.S. Treasury securities
Marketable Securities [Line Items]
Short-term marketable securities	10,133	3,855
Corporate notes and bonds
Marketable Securities [Line Items]
Short-term marketable securities	38,036	32,729
Commercial paper
Marketable Securities [Line Items]
Short-term marketable securities	4,687	1,595
Commercial paper
Marketable Securities [Line Items]
Total cash equivalents	$ 8,126	$ 2,048

SIGNIFICANT ACCOUNTING POLICIES (Credit Concentration) (Details) - customer	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounts receivable
Restricted Cash and Cash Equivalents Items [Line Items]
Concentration risk number of major customers over benchmark	0	0	0
Concentration risk benchmark (as a percent)	10.00%	10.00%	10.00%
Total Revenues
Restricted Cash and Cash Equivalents Items [Line Items]
Concentration risk number of major customers over benchmark	0	0	0
Concentration risk benchmark (as a percent)	10.00%	10.00%	10.00%

SIGNIFICANT ACCOUNTING POLICIES (Property, Plant and Equipment) (Details)	12 Months Ended
	Dec. 31, 2018
Minimum \| Buildings
Property, Plant and Equipment [Line Items]
Weighted average remaining useful life (in years)	20 years
Minimum \| Leasehold and building improvements
Property, Plant and Equipment [Line Items]
Weighted average remaining useful life (in years)	2 years
Minimum \| Camp and lodging equipment
Property, Plant and Equipment [Line Items]
Weighted average remaining useful life (in years)	8 years
Minimum \| Vehicles
Property, Plant and Equipment [Line Items]
Weighted average remaining useful life (in years)	2 years
Minimum \| Capitalized software and computer equipment
Property, Plant and Equipment [Line Items]
Weighted average remaining useful life (in years)	3 years
Minimum \| Containers and railcars
Property, Plant and Equipment [Line Items]
Weighted average remaining useful life (in years)	8 years
Minimum \| All other equipment
Property, Plant and Equipment [Line Items]
Weighted average remaining useful life (in years)	4 years
Minimum \| Furniture and fixtures
Property, Plant and Equipment [Line Items]
Weighted average remaining useful life (in years)	5 years
Maximum \| Buildings
Property, Plant and Equipment [Line Items]
Weighted average remaining useful life (in years)	42 years
Maximum \| Leasehold and building improvements
Property, Plant and Equipment [Line Items]
Weighted average remaining useful life (in years)	45 years
Maximum \| Camp and lodging equipment
Property, Plant and Equipment [Line Items]
Weighted average remaining useful life (in years)	15 years
Maximum \| Vehicles
Property, Plant and Equipment [Line Items]
Weighted average remaining useful life (in years)	15 years
Maximum \| Capitalized software and computer equipment
Property, Plant and Equipment [Line Items]
Weighted average remaining useful life (in years)	5 years
Maximum \| Containers and railcars
Property, Plant and Equipment [Line Items]
Weighted average remaining useful life (in years)	16 years
Maximum \| All other equipment
Property, Plant and Equipment [Line Items]
Weighted average remaining useful life (in years)	30 years
Maximum \| Furniture and fixtures
Property, Plant and Equipment [Line Items]
Weighted average remaining useful life (in years)	8 years

SIGNIFICANT ACCOUNTING POLICIES (Goodwill and Intangible Assets) (Details)	12 Months Ended
	Dec. 31, 2018
Minimum \| Permits
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life (in years)	5 years
Minimum \| Other intangible assets
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life (in years)	5 years
Maximum \| Permits
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life (in years)	30 years
Maximum \| Other intangible assets
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life (in years)	20 years

SIGNIFICANT ACCOUNTING POLICIES (Landfill Accounting) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) service_location expansion landfill_site cubic_yard	Dec. 31, 2017 USD ($) cubic_yard	Dec. 31, 2016 USD ($) cubic_yard
Property, Plant and Equipment [Line Items]
Application approvals, acceptance period (in years)	5 years
Number of unpermitted expansions \| expansion	1
Number of service locations \| service_location	1
Percentage of airspace remaining (as a percent)	16.20%
Landfill sites \| landfill_site	11
Remaining highly probable airspace	29,760,000
Permitted, but not highly probable airspace (cubic yards)	0	0
Remaining Airspace Capacity [Roll Forward]
Remaining capacity, beginning of period (cubic yards)	31,113,000	32,228,000	29,786,000
Changes in highly probable airspace, net (cubic yards)	(223,000)	0	3,464,000
Consumed (cubic yards)	(1,130,000)	(1,115,000)	(1,022,000)
Remaining capacity, end of period (cubic yards)	29,760,000	31,113,000	32,228,000
Landfill final closure and post-closure liabilities \| $	$ 37.8	$ 32.4
Regulatory post-closure period for landfill (in years)	30 years
Asset retirement obligations, inflation rate (as a percent)	1.02%	1.02%
Asset retirement obligations, risk free rate (as a percent)	5.66%	6.32%
Non-landfill closure and post-closure liabilities \| $	$ 32.1	$ 28.6
Minimum
Remaining Airspace Capacity [Roll Forward]
Non-landfill closure and post-closure liabilities, period (in years)	10 years
Maximum
Remaining Airspace Capacity [Roll Forward]
Non-landfill closure and post-closure liabilities, period (in years)	30 years
Landfill assets
Property, Plant and Equipment [Line Items]
Amortization \| $	$ 10.3	$ 9.5	$ 9.7
Non-commercial landfills
Property, Plant and Equipment [Line Items]
Landfill sites \| landfill_site	2
Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	24,930,000
Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	4,830,000
Altair \| Texas
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	3 years
Remaining highly probable airspace	311,000
Altair \| Texas \| Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	311,000
Altair \| Texas \| Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0
Buttonwillow \| California
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	21 years
Remaining highly probable airspace	6,234,000
Buttonwillow \| California \| Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	6,234,000
Buttonwillow \| California \| Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0
Deer Park \| Texas
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	4 years
Remaining highly probable airspace	141,000
Deer Park \| Texas \| Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	141,000
Deer Park \| Texas \| Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0
Deer Trail \| Colorado
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	28 years
Remaining highly probable airspace	1,755,000
Deer Trail \| Colorado \| Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	1,755,000
Deer Trail \| Colorado \| Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0
Grassy Mountain \| Utah
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	51 years
Remaining highly probable airspace	5,024,000
Grassy Mountain \| Utah \| Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	194,000
Grassy Mountain \| Utah \| Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	4,830,000
Kimball \| Nebraska
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	9 years
Remaining highly probable airspace	190,000
Kimball \| Nebraska \| Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	190,000
Kimball \| Nebraska \| Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0
Lambton \| Ontario
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	64 years
Remaining highly probable airspace	4,821,000
Lambton \| Ontario \| Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	4,821,000
Lambton \| Ontario \| Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0
Lone Mountain \| Oklahoma
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	18 years
Remaining highly probable airspace	4,124,000
Lone Mountain \| Oklahoma \| Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	4,124,000
Lone Mountain \| Oklahoma \| Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0
Ryley \| Alberta
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	7 years
Remaining highly probable airspace	906,000
Ryley \| Alberta \| Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	906,000
Ryley \| Alberta \| Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0
Sawyer \| North Dakota
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	87 years
Remaining highly probable airspace	3,522,000
Sawyer \| North Dakota \| Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	3,522,000
Sawyer \| North Dakota \| Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0
Westmorland \| California
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	64 years
Remaining highly probable airspace	2,732,000
Westmorland \| California \| Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	2,732,000
Westmorland \| California \| Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0

SIGNIFICANT ACCOUNTING POLICIES (Remedial Liabilities) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) site	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Regulatory Liabilities [Line Items]
Remedial Liability \| $	$ 121,017	$ 124,468	$ 128,007
Period of time over which business acquisitions have been acquired (in years)	16 years
Superfund sites \| site	128
Minimum
Regulatory Liabilities [Line Items]
Remedial liabilities at acquisition, inflation rate (as a percent)	1.01%
Remedial liabilities at acquisition, risk-free interest rate (as a percent)	1.37%
Maximum
Regulatory Liabilities [Line Items]
Remedial liabilities at acquisition, inflation rate (as a percent)	2.57%
Remedial liabilities at acquisition, risk-free interest rate (as a percent)	5.99%

SIGNIFICANT ACCOUNTING POLICIES (Recent Accounting Pronouncements) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other (expense) income, net	$ (4,061,000)	$ (996,000)	$ 846,000	$ (299,000)	$ (3,305,000)	$ (432,000)	$ (833,000)	$ (1,549,000)	$ (4,510,000)	$ (6,119,000)	$ 6,195,000
Cumulative effect of change in accounting principle	(1,564,000)				231,000				(1,564,000)	231,000
ASU 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other (expense) income, net	1,400,000
Accumulated Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of change in accounting principle	$ (1,564,000)				(450,000)				$ (1,564,000)	(450,000)
Accumulated Earnings \| ASU 2016-16
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of change in accounting principle					$ (1,600,000)					$ (1,600,000)
Scenario, Forecast \| Minimum \| ASU 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right-of-use assets												$ 180,000,000
Operating liabilities												180,000,000
Scenario, Forecast \| Maximum \| ASU 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right-of-use assets												220,000,000
Operating liabilities												$ 220,000,000

BUSINESS COMBINATIONS (2018 Acquisitions Narrative) (Details) - USD ($) $ in Thousands			12 Months Ended
	Aug. 31, 2018	Feb. 23, 2018	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Goodwill amount			$ 40,704	$ 8,687
Acquired Company Included in Safety-Kleen and Environmental Services Segments [Member]
Business Acquisition [Line Items]
Goodwill amount	$ 15,800
Veolia Division
Business Acquisition [Line Items]
Purchase price		$ 124,000
Revenue from acquisition included in the company's result of operations			154,000
Pre-tax income			900
Depreciation expense on property, plant and equipment			14,600
Amortization expense related to intangible assets			600
Acquisition-related costs			$ 1,400
Weighted average useful life (in years)		8 years 2 months

REVENUES (Disaggregation of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Revenues	$ 858,204	$ 843,181	$ 849,140	$ 749,778	$ 747,403	$ 755,846	$ 752,788	$ 688,941	$ 3,300,303	$ 2,944,978	$ 2,755,226
United States
Disaggregation of Revenue [Line Items]
Revenues									2,796,145
Canada
Disaggregation of Revenue [Line Items]
Revenues									504,158
Technical Services
Disaggregation of Revenue [Line Items]
Revenues									1,037,388
Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Revenues									304,727
Industrial Services
Disaggregation of Revenue [Line Items]
Revenues									541,895
Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Revenues									120,938
Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Revenues									795,077
Kleen Performance Products
Disaggregation of Revenue [Line Items]
Revenues									500,278
Environmental Services
Disaggregation of Revenue [Line Items]
Revenues									2,003,843	1,728,700	1,641,432
Environmental Services \| United States
Disaggregation of Revenue [Line Items]
Revenues									1,598,402
Environmental Services \| Canada
Disaggregation of Revenue [Line Items]
Revenues									405,441
Environmental Services \| Technical Services
Disaggregation of Revenue [Line Items]
Revenues									1,037,388
Environmental Services \| Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Revenues									304,727
Environmental Services \| Industrial Services
Disaggregation of Revenue [Line Items]
Revenues									541,895
Environmental Services \| Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Revenues									119,833
Environmental Services \| Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Revenues									0
Environmental Services \| Kleen Performance Products
Disaggregation of Revenue [Line Items]
Revenues									0
Safety-Kleen
Disaggregation of Revenue [Line Items]
Revenues									1,295,355	1,213,703	1,110,727
Safety-Kleen \| United States
Disaggregation of Revenue [Line Items]
Revenues									1,196,661
Safety-Kleen \| Canada
Disaggregation of Revenue [Line Items]
Revenues									98,694
Safety-Kleen \| Technical Services
Disaggregation of Revenue [Line Items]
Revenues									0
Safety-Kleen \| Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Revenues									0
Safety-Kleen \| Industrial Services
Disaggregation of Revenue [Line Items]
Revenues									0
Safety-Kleen \| Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Revenues									0
Safety-Kleen \| Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Revenues									795,077
Safety-Kleen \| Kleen Performance Products
Disaggregation of Revenue [Line Items]
Revenues									500,278
Corporate Items
Disaggregation of Revenue [Line Items]
Revenues									1,105	$ 2,575	$ 3,067
Corporate Items \| United States
Disaggregation of Revenue [Line Items]
Revenues									1,082
Corporate Items \| Canada
Disaggregation of Revenue [Line Items]
Revenues									23
Corporate Items \| Technical Services
Disaggregation of Revenue [Line Items]
Revenues									0
Corporate Items \| Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Revenues									0
Corporate Items \| Industrial Services
Disaggregation of Revenue [Line Items]
Revenues									0
Corporate Items \| Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Revenues									1,105
Corporate Items \| Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Revenues									0
Corporate Items \| Kleen Performance Products
Disaggregation of Revenue [Line Items]
Revenues									$ 0

BUSINESS COMBINATIONS (2018 Acquisition) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Goodwill	$ 514,189	$ 478,523	$ 465,154
Veolia Division
Business Acquisition [Line Items]
Accounts receivable	38,201
Inventories and supplies	1,126
Prepaid expenses and other current assets	828
Property, plant and equipment	72,243
Permits and other intangibles	5,140
Current liabilities	(18,025)
Closure and post-closure liabilities, less current portion	(354)
Total identifiable net assets	99,159
Goodwill	24,873
Total purchase price, net of cash acquired	$ 124,032

REVENUES (Contract Balances) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Revenue from Contract with Customer [Abstract]
Receivables	$ 606,952	$ 528,924
Contract Assets (Unbilled Receivables)	54,794	35,922
Contract Liabilities (Deferred Revenue)	$ 61,843	$ 67,822

BUSINESS COMBINATIONS (2017 Acquisitions) (Details) $ / shares in Units, $ in Thousands, $ in Millions				12 Months Ended
	Jul. 14, 2017 CAD ($) $ / shares	Jul. 14, 2017 USD ($)	Jan. 31, 2017 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jul. 14, 2017 USD ($)
Business Acquisition [Line Items]
Goodwill amount				$ 40,704	$ 8,687
Lonestar
Business Acquisition [Line Items]
Goodwill amount		$ 2,800
Payments to acquire businesses	$ 41.8	$ 33,100
Equity payout (in CAD per share) \| $ / shares	$ 0.72
Debt assumed	$ 21.3					$ 16,800
2017 Acquisitions
Business Acquisition [Line Items]
Purchase price			$ 11,900
Goodwill amount			$ 5,000
Revenue from acquisition included in the company's result of operations					$ 14,500

REVENUES (Narrative) (Details) - Veolia Division $ in Millions	Feb. 23, 2018 USD ($)
Business Acquisition [Line Items]
Acquired receivables	$ 20.8
Acquired contract assets	$ 17.4

BUSINESS COMBINATIONS (2016 Acquisitions Narrative) (Details) - 2016 Acquisitions $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) aquisition
Business Acquisition [Line Items]
Number of businesses acquired \| aquisition	7
Purchase price	$ 204.8
Revenue from acquisition included in the company's result of operations	69.8
Acquisition related costs	$ 1.7

BUSINESS COMBINATIONS (2016 Acquisitions) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Goodwill	$ 514,189	$ 478,523		$ 465,154
2016 Acquisitions
Business Acquisition [Line Items]
Accounts receivable			$ 16,242
Inventories and supplies			12,688
Prepaid expenses and other current assets			752
Property, plant and equipment			143,916
Permits and other intangibles			28,856
Current liabilities			(19,905)
Closure and post-closure liabilities, less current portion			(3,004)
Remedial liabilities, less current portion			(2,545)
Deferred taxes, unrecognized tax benefits and other long-term liabilities			(20,219)
Total identifiable net assets			156,781
Goodwill			47,977
Total purchase price, net of cash acquired			$ 204,758

DISPOSITION OF BUSINESS (2017 Disposition Narrative) (Details) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
	Jun. 30, 2017	Jun. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale of businesses		$ 31,700	$ 0	$ 30,732	$ 16,884
Transformer Services \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale	$ 45,500	$ 45,500
Proceeds from sale, net of transactional related costs	43,400
Transition costs	$ 2,100

DISPOSITION OF BUSINESS (2017 Dispositions) (Details) - Transformer Services - Disposal Group, Disposed of by Sale, Not Discontinued Operations $ in Thousands	Jun. 30, 2017 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total current assets	$ 7,241
Property, plant and equipment, net	8,773
Total other assets	1,681
Total assets divested	17,695
Total current liabilities	3,849
Total other liabilities	1,170
Total liabilities divested	5,019
Net carrying value divested	$ 12,676

DISPOSITION OF BUSINESS DISPOSITION OF BUSINESS (Income (Loss) Attributable to Transformer Services) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Transformer Services \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income before provision (benefit) for income taxes	$ 2,771	$ 4,187

DISPOSITION OF BUSINESS (2016 Disposition Narrative) (Details) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
	Sep. 01, 2016	Jun. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale of businesses		$ 31,700	$ 0	$ 30,732	$ 16,884
Catalyst Services \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale	$ 50,600					$ 2,000
Proceeds from sale, net of cash divested	$ 49,200
Transition costs					$ 1,600

DISPOSITION OF BUSINESS (2016 Disposition) (Details) - Catalyst Services - Disposal Group, Disposed of by Sale, Not Discontinued Operations $ in Thousands	Sep. 01, 2016 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total current assets	$ 19,019
Property, plant and equipment, net	11,154
Total other assets	6,500
Total assets divested	36,673
Total current liabilities	4,040
Total other liabilities	566
Total liabilities divested	4,606
Net carrying value divested	$ 32,067

DISPOSITION OF BUSINESS (Income (Loss) Attributable to Catalyst Services) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($)
Catalyst Services \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income before provision (benefit) for income taxes	$ 290

INVENTORIES AND SUPPLIES (Details) - USD ($) $ in Thousands	12 Months Ended
INVENTORIES AND SUPPLIES (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Inventory Disclosure [Abstract]
Oil and oil related products	$ 70,823	$ 58,142
Supplies and drums	104,609	94,242
Solvent and solutions	10,657	9,167
Modular camp accommodations	0	1,826
Other	13,390	12,635
Total inventories and supplies	199,479	176,012
Transfer of inventory to property, plant and equipment	$ 0	$ 12,641	$ 0

PROPERTY, PLANT, AND EQUIPMENT (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 3,332,595	$ 3,190,573
Less - accumulated depreciation and amortization	1,770,617	1,603,208
Total property, plant and equipment, net	1,561,978	1,587,365
Interest capitalization	600	600	$ 5,500
Depreciation inclusive of landfill amortization	264,300	251,400	$ 247,000
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	123,734	121,658
Asset retirement costs (non-landfill)
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	15,148	14,593
Landfill assets
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	154,918	144,539
Buildings and improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	440,188	414,384
Camp and lodging equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	152,998	170,012
Vehicles
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	721,735	617,959
Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,697,490	1,644,102
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	5,453	5,708
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 20,931	$ 57,618

GOODWILL AND OTHER INTANGIBLE ASSETS (Changes to Goodwill) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Goodwill, beginning of period	$ 478,523	$ 465,154
Increase from current period acquisitions	40,704	8,687
Measurement period adjustments from prior period acquisitions	(78)	2,186
Decrease from disposition of business		(1,300)
Goodwill impairment charge	0	0	$ (34,013)
Foreign currency translation	(4,960)	3,796
Goodwill, end of period	514,189	478,523	465,154
Environmental Services
Goodwill [Roll Forward]
Goodwill, beginning of period	172,386	169,084
Increase from current period acquisitions	37,007	3,000
Measurement period adjustments from prior period acquisitions	(78)	0
Decrease from disposition of business		(1,300)
Foreign currency translation	(2,296)	1,602
Goodwill, end of period	207,019	172,386	169,084
Safety-Kleen
Goodwill [Roll Forward]
Goodwill, beginning of period	306,137	296,070
Increase from current period acquisitions	3,697	5,687
Measurement period adjustments from prior period acquisitions	0	2,186
Decrease from disposition of business		0
Foreign currency translation	(2,664)	2,194
Goodwill, end of period	$ 307,170	$ 306,137	$ 296,070

GOODWILL AND OTHER INTANGIBLE ASSETS (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Indefinite-lived Intangible Assets [Line Items]
Accumulated goodwill impairment charges	$ 189,400
Goodwill impairment charge	0	$ 0	$ 34,013
Intangible assets	441,875	469,128
Amortization expense of permits and other intangible assets	$ 34,400	$ 37,000	40,000
Lodging Segment
Indefinite-lived Intangible Assets [Line Items]
Goodwill impairment charge			$ 34,000

GOODWILL AND OTHER INTANGIBLE ASSETS (Finite-lived and Indefinite Lived Intangible Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Finite-lived intangible assets
Cost	$ 608,332	$ 610,711
Accumulated Amortization	288,925	264,911
Net	319,407	345,800
Total permits and other intangible assets, cost	730,800	734,039
Total permits and other intangible assets, net	441,875	469,128
Trademarks and trade names
Finite-lived intangible assets
Trademarks and trade names	122,468	123,328
Permits
Finite-lived intangible assets
Cost	177,583	174,721
Accumulated Amortization	79,358	74,347
Net	98,225	100,374
Customer and supplier relationships
Finite-lived intangible assets
Cost	393,487	399,224
Accumulated Amortization	179,824	158,972
Net	213,663	240,252
Other intangible assets
Finite-lived intangible assets
Cost	37,262	36,766
Accumulated Amortization	29,743	31,592
Net	$ 7,519	$ 5,174

GOODWILL AND OTHER INTANGIBLE ASSETS (Expected Amortization) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Expected amortization
2019	$ 33,091
2020	30,195
2021	27,553
2022	27,386
2023	23,468
Thereafter	177,714
Net	$ 319,407	$ 345,800

ACCRUED EXPENSES - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Payables and Accruals [Abstract]
Insurance	$ 70,217	$ 57,889
Interest	3,930	12,660
Accrued compensation and benefits	77,881	55,861
Income, real estate, sales and other taxes	25,670	27,330
Other	55,707	34,242
Total accrued expenses	$ 233,405	$ 187,982

ACCRUED EXPENSES - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Payables and Accruals [Abstract]
Accrued health insurance	$ 14.7	$ 9.0
Accrual loss for workers' compensation, comprehensive general liability and vehicle liability self-insurance programs	53.9	47.9
Accrued compensation and benefits increase	22.0
Accrued legal matters	7.5	1.4
Accrued severance charges	2.7	$ 3.5
Derivative liability	$ 8.8

CLOSURE AND POST-CLOSURE LIABILITIES (Changes in Post-Closure Liabilities) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Changes to post-closure liabilities
Balance at the beginning of the period	$ 61,037	$ 58,331
Liabilities assumed in acquisitions	685	59
Measurement period adjustments from prior period acquisitions		596
New asset retirement obligations	2,518	1,881
Adjustment related to disposition of business	(5,104)	(1,170)
Accretion		4,748
Changes in estimates recorded to statement of operations	1,460	(240)
Changes in estimates recorded to balance sheet	1,931	(227)
Expenditures	(2,281)	(3,225)
Currency translation and other	(523)	284
Balance at the end of the period	69,931	$ 61,037
Increase in facility closure costs	$ 1,200
Asset retirement obligations, risk free rate (as a percent)	5.66%	6.32%
Landfill Retirement Liability
Changes to post-closure liabilities
Balance at the beginning of the period	$ 32,382	$ 30,630
Liabilities assumed in acquisitions	0	0
Measurement period adjustments from prior period acquisitions		0
New asset retirement obligations	2,518	1,881
Adjustment related to disposition of business	(2,537)	0
Accretion		2,243
Changes in estimates recorded to statement of operations	(37)	(131)
Changes in estimates recorded to balance sheet	1,867	364
Expenditures	(1,224)	(2,777)
Currency translation and other	(234)	172
Balance at the end of the period	37,809	32,382
Non-Landfill Retirement Liability
Changes to post-closure liabilities
Balance at the beginning of the period	28,655	27,701
Liabilities assumed in acquisitions	685	59
Measurement period adjustments from prior period acquisitions		596
New asset retirement obligations	0	0
Adjustment related to disposition of business	(2,567)	(1,170)
Accretion		2,505
Changes in estimates recorded to statement of operations	1,497	(109)
Changes in estimates recorded to balance sheet	64	(591)
Expenditures	(1,057)	(448)
Currency translation and other	(289)	112
Balance at the end of the period	$ 32,122	$ 28,655

CLOSURE AND POST-CLOSURE LIABILITIES (Anticipated Payments) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Environmental Property Sale, Disposal or Abandonment Costs
2019	$ 10,574
2020	9,424
2021	10,941
2022	7,626
2023	9,264
Thereafter	271,314
Undiscounted closure and post-closure liabilities	319,143
Less: Discount at credit-adjusted risk-free rate	(155,999)
Less: Undiscounted estimated closure and post-closure liabilities relating to airspace not yet consumed	(93,213)
Present value of closure and post-closure liabilities	$ 69,931	$ 61,037	$ 58,331

REMEDIAL LIABILITIES (Changes in Remedial Liabilities) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Changes to remedial liabilities
Balance at the beginning of the period	$ 124,468	$ 128,007
Measurement period adjustments from prior period acquisitions		504
Accretion	4,702	4,712
Changes in estimates recorded to statement of operations	687	45
Expenditures	(7,834)	(9,740)
Currency translation and other	(1,006)	940
Balance at the end of the period	121,017	124,468
Remedial Liabilities for Landfill Sites
Changes to remedial liabilities
Balance at the beginning of the period	1,800	1,777
Measurement period adjustments from prior period acquisitions		0
Accretion	86	86
Changes in estimates recorded to statement of operations	(1)	(21)
Expenditures	(47)	(42)
Currency translation and other	0	0
Balance at the end of the period	1,838	1,800
Remedial Liabilities for Inactive Sites
Changes to remedial liabilities
Balance at the beginning of the period	65,342	64,151
Measurement period adjustments from prior period acquisitions		0
Accretion	2,745	2,648
Changes in estimates recorded to statement of operations	130	(289)
Expenditures	(3,759)	(3,906)
Currency translation and other	857	2,738
Balance at the end of the period	65,315	65,342
Remedial Liabilities (Including Superfund) for Non-Landfill Operations
Changes to remedial liabilities
Balance at the beginning of the period	57,326	62,079
Measurement period adjustments from prior period acquisitions		504
Accretion	1,871	1,978
Changes in estimates recorded to statement of operations	558	355
Expenditures	(4,028)	(5,792)
Currency translation and other	(1,863)	(1,798)
Balance at the end of the period	$ 53,864	$ 57,326

REMEDIAL LIABILITIES (Additional Information) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Environmental Remediation Obligations [Abstract]
Changes in estimates recorded to statement of income (loss)	$ 687	$ 45
Future remediation liability	121,017	$ 124,468	$ 128,007
Possible increase in total remedial liabilities	$ 22,800
Accrual for environmental loss contingencies, threshold for disclosure (as a percent)	5.00%

REMEDIAL LIABILITIES (Anticipated Payments) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accrual for Environmental Loss Contingencies, Net [Abstract]
2019	$ 13,975
2020	15,467
2021	14,593
2022	9,560
2023	8,688
Thereafter	81,453
Undiscounted remedial liabilities	143,736
Less: Discount	(22,719)
Total remedial liabilities	$ 121,017	$ 124,468	$ 128,007

REMEDIAL LIABILITIES (Estimates) (Details) $ in Thousands	12 Months Ended
REMEDIAL LIABILITIES (Estimates) (Details) $ in Thousands	Dec. 31, 2018 USD ($) site facility	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Site Contingency [Line Items]
Remedial Liability	$ 121,017	$ 124,468	$ 128,007
% of Total	100.00%
Reasonably possible additional liabilities	$ 22,770
Legal and Administrative Proceedings
Site Contingency [Line Items]
Remedial Liability	17,900
Reasonably possible additional liabilities	1,800
Facilities now used in active conduct of the Company's business (41 facilities)
Site Contingency [Line Items]
Remedial Liability	$ 48,506
% of Total	40.10%
Reasonably possible additional liabilities	$ 11,171
Number of facility by type \| facility	41
Inactive facilities not now used in active conduct of the Company's business but most of which were acquired because the assumption of remedial liabilities for such facilities was part of the purchase price for the CSD assets (35 facilities)
Site Contingency [Line Items]
Remedial Liability	$ 64,344
% of Total	53.20%
Reasonably possible additional liabilities	$ 10,782
Number of facility by type \| facility	35
Superfund sites owned by third parties (17 sites)
Site Contingency [Line Items]
Remedial Liability	$ 8,167
% of Total	6.70%
Reasonably possible additional liabilities	$ 817
Number of facility by type \| site	17
Superfund sites owned by third parties (17 sites) \| Various
Site Contingency [Line Items]
Remedial Liability	$ 8,167
% of Total	6.70%
Reasonably possible additional liabilities	$ 817
Number of facility by type \| site	17
Closed incinerator and landfill \| Baton Rouge LA
Site Contingency [Line Items]
Remedial Liability	$ 23,314
% of Total	19.30%
Reasonably possible additional liabilities	$ 3,963
Closed incinerator \| Bridgeport, NJ
Site Contingency [Line Items]
Remedial Liability	$ 18,616
% of Total	15.40%
Reasonably possible additional liabilities	$ 2,577
Idled incinerator and legal proceedings \| Mercier Quebec
Site Contingency [Line Items]
Remedial Liability	$ 9,809
% of Total	8.10%
Reasonably possible additional liabilities	$ 1,037
Operating solvent recycling center \| Linden, NJ
Site Contingency [Line Items]
Remedial Liability	$ 7,487
% of Total	6.20%
Reasonably possible additional liabilities	$ 790
All other incinerators, landfills, wastewater treatment facilities and service centers (72 facilities) \| Various
Site Contingency [Line Items]
Remedial Liability	$ 53,624
% of Total	44.30%
Reasonably possible additional liabilities	$ 13,586
Number of facility by type \| facility	72

FINANCING ARRANGEMENTS (Summary of Financing Arrangements) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2012	Jul. 30, 2012
Debt Instrument [Line Items]
Current portion of long-term obligations	$ 7,535	$ 4,000
Long-term obligations, at par	1,579,697	1,639,000
Unamortized debt issuance costs and premium, net	(14,676)	(13,463)
Long-term obligations, at carrying value	1,565,021	1,625,537
Secured Debt \| Term Loan Agreement
Debt Instrument [Line Items]
Current portion of long-term obligations	7,535	4,000
Long-term obligations, at par	734,697	394,000
Senior Notes \| Senior unsecured notes, at 5.25%, due August 1, 2020 (2020 Notes)
Debt Instrument [Line Items]
Long-term obligations, at par	$ 0	400,000
Interest rate (as a percent)	5.25%			5.25%
Senior Notes \| Senior unsecured notes, at 5.125%, due June 1, 2021 (2021 Notes)
Debt Instrument [Line Items]
Long-term obligations, at par	$ 845,000	$ 845,000
Interest rate (as a percent)	5.125%		5.125%

FINANCING ARRANGEMENTS (Narrative) (Details)				3 Months Ended	12 Months Ended
FINANCING ARRANGEMENTS (Narrative) (Details)	Aug. 02, 2018	Aug. 01, 2018 USD ($)	Jul. 19, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2018 USD ($)	Apr. 17, 2018	Sep. 30, 2017	Mar. 14, 2016 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2012 USD ($)	Jul. 30, 2012 USD ($)
Financing arrangements
Borrowing from revolving credit facility					$ 50,000,000	$ 0	$ 0
Settlement of borrowing					50,000,000	0	$ 0
Revolving credit facility, available borrowing capacity				$ 235,400,000	235,400,000	217,800,000
Letters of credit outstanding, amount				130,100,000	130,100,000	134,100,000
Effective interest rate (as a percent)	4.67%
Derivative liability				8,800,000	$ 8,800,000
Eurodollar
Financing arrangements
Basis spread on variable rate (as a percent)	1.75%
Parent and Domestic Subsidiaries
Financing arrangements
Credit available subject to percentage of accounts receivable (as a percent)					85.00%
Credit available subject to percentage of cash deposited (as a percent)					100.00%
Canadian Subsidiaries
Financing arrangements
Credit available subject to percentage of accounts receivable (as a percent)					85.00%
Credit available subject to percentage of cash deposited (as a percent)					100.00%
Term Loan Agreement
Financing arrangements
Increase in principal amount of initial term loans			$ 350,000,000.0
Debt outstanding				742,200,000	$ 742,200,000
Senior unsecured notes, at 5.25%, due August 1, 2020 (2020 Notes)
Financing arrangements
Purchase price			330,900,000
Accrued interest			7,900,000
Debt redemption fees			1,000,000
Term Loans with Interest Rate Swap Agreements
Financing arrangements
Debt outstanding								$ 350,000,000
Secured Debt \| First Amendment \| Eurodollar
Financing arrangements
Reduction of applicable interest rate margin									0.0025
Interest rate (as a percent)									1.75%
Secured Debt \| First Amendment \| Base rate loans
Financing arrangements
Reduction of applicable interest rate margin									0.0025
Interest rate (as a percent)									0.75%
Secured Debt \| Term Loan Agreement
Financing arrangements
Fair value of notes				$ 707,000,000	$ 707,000,000	400,500,000
Effective interest rate (as a percent)										4.27%
Senior Notes \| Senior unsecured notes, at 5.25%, due August 1, 2020 (2020 Notes)
Financing arrangements
Interest rate (as a percent)				5.25%	5.25%									5.25%
Redemption of 2020 Notes		$ 78,000,000	$ 322,000,000
Fair value of notes						404,600,000
Face amount														$ 800,000,000
Repurchased amount				$ 400,000,000	$ 400,000,000	400,000,000.0
Senior Notes \| Senior unsecured notes, at 5.125%, due June 1, 2021 (2021 Notes)
Financing arrangements
Interest rate (as a percent)				5.125%	5.125%								5.125%
Fair value of notes				$ 845,000,000	$ 845,000,000	855,700,000
Face amount											$ 250,000,000.0		$ 600,000,000.0
Repurchased amount												$ 5,000,000.0
Revolving credit facility
Financing arrangements
Revolving credit facility, maximum borrowing capacity				400,000,000.0	$ 400,000,000.0
Period for measurement of average liquidity (in days)					30 days
Revolving credit facility \| Minimum
Financing arrangements
Commitment fee (as a percent)					0.25%
Revolving credit facility \| Minimum \| LIBOR loans
Financing arrangements
Basis spread on variable rate (as a percent)					1.25%
Revolving credit facility \| Minimum \| Base rate loans
Financing arrangements
Basis spread on variable rate (as a percent)					0.25%
Revolving credit facility \| Maximum
Financing arrangements
Commitment fee (as a percent)					0.30%
Revolving credit facility \| Maximum \| LIBOR loans
Financing arrangements
Basis spread on variable rate (as a percent)					1.50%
Revolving credit facility \| Maximum \| Base rate loans
Financing arrangements
Basis spread on variable rate (as a percent)					0.50%
Revolving credit facility \| Parent and Domestic Subsidiaries
Financing arrangements
Revolving credit facility, maximum borrowing capacity				300,000,000	$ 300,000,000
Revolving credit facility \| Canadian Subsidiaries
Financing arrangements
Revolving credit facility, maximum borrowing capacity				100,000,000	100,000,000
Letters of credit \| Parent and Domestic Subsidiaries
Financing arrangements
Revolving credit facility, maximum borrowing capacity				250,000,000	250,000,000
Letters of credit \| Canadian Subsidiaries
Financing arrangements
Revolving credit facility, maximum borrowing capacity				75,000,000	75,000,000
Interest rate swap
Financing arrangements
Basis spread on variable rate (as a percent)	2.92%
Notional amount of interest rate swap agreements								$ 350,000,000.0
Revolving credit facility \| Revolving credit facility
Financing arrangements
Borrowing from revolving credit facility		$ 50,000,000
Settlement of borrowing				50,000,000
Debt outstanding				$ 0	$ 0	$ 0

INCOME TAXES (Provision for Tax Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Noncontrolling Interest [Abstract]
Domestic	$ 115,070	$ 101,714	$ 87,328
Foreign	(20,588)	(43,025)	(78,612)
(Loss) income before (benefit) provision for income taxes	94,482	58,689	8,716
Current:
Federal	(7,677)	25,613	14,798
State	12,653	11,083	8,763
Foreign	4,781	4,589	9,844
Current Income Tax Expense (Benefit)	9,757	41,285	33,405
Deferred
Federal	19,899	(85,488)	21,814
State	(1,205)	1,085	1,644
Foreign	395	1,068	(8,274)
Deferred income taxes	19,089	(83,335)	15,184
Provision (benefit) for income taxes	28,846	(42,050)	48,589
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Tax expense at US statutory rate	19,841	20,541	3,051
State income taxes, net of federal benefit	8,711	4,547	6,010
Foreign rate differential	(1,124)	3,733	3,646
Valuation allowance	10,466	16,552	22,564
Uncertain tax position interest and penalties	(1,806)	3,730	107
Goodwill impairment	0	0	11,905
Tax credits	(9,799)	0	0
Other	2,845	1,856	1,306
Adjustment for Tax Cuts and Jobs Act	(288)	(93,009)	0
Provision (benefit) for income taxes	$ 28,846	$ (42,050)	$ 48,589

INCOME TAXES (Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Provision for doubtful accounts	$ 10,715	$ 7,417
Closure, post-closure and remedial liabilities	28,380	28,189
Accrued expenses	15,686	15,382
Accrued compensation	7,774	1,903
Net operating loss carryforwards	43,284	46,650
Tax credit carryforwards	16,909	17,504
Uncertain tax positions accrued interest and federal benefit	519	921
Stock-based compensation	3,440	2,268
Other	7,067	3,258
Total deferred tax assets	133,774	123,492
Deferred tax liabilities:
Property, plant and equipment	(164,246)	(144,325)
Permits and other intangible assets	(103,539)	(107,407)
Prepaids	(9,187)	(8,080)
Total deferred tax liabilities	(276,972)	(259,812)
Total net deferred tax liability before valuation allowance	(143,198)	(136,320)
Less valuation allowance	(79,295)	(68,355)
Net deferred tax liabilities	(222,493)	$ (204,675)
State and local operating loss carryforwards	185,100
Federal operating loss carryforwards	49,800
Foreign operating loss carryforwards	103,300
Foreign tax credit carryforwards	$ 16,500

INCOME TAXES (Additional Information) (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended	12 Months Ended
	Oct. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Effective income tax rate (as a percent)			30.50%	(71.60%)	557.50%
Net benefit from enacted tax act		$ (93,000)	$ 300
Tax benefit for the remeasurement of deferred tax assets and liabilities		100,500		$ 100,500
One-time tax expense on deemed repatriation		7,500		7,500
One-time deemed repatriation, adjusted				6,600
Adjustment from one-time deemed repatriation to tax expense			900
Tax benefit due to reduction in net deferred tax liability		93,000		99,900
Deferred expense			600
Benefit to income tax expense	$ 3,300		9,800
Additional income tax benefit upon amendments of 2014 through 2016 tax returns	$ (7,100)
Valuation allowance		68,355	79,295	68,355
Valuation allowance, foreign tax credits		17,500	16,500	17,500
Valuation allowance, federal net operating loss carryforwards		3,900	800	3,900
Valuation allowance, state net operating loss carryforwards		11,900	9,600	11,900
Valuation allowance, foreign net operating loss carryforwards		22,600	22,700	22,600
Valuation allowance, deferred tax assets of Canadian subsidiary		12,500	26,600	12,500
Valuation allowance, deferred tax assets of Canadian subsidiary, tax attributes			3,100
Unrecognized tax benefits that would impact effective tax rate		5,100	3,200	5,100	$ 1,700
Unrecognized tax benefits, income tax penalties and interest accrued		$ 900	800	900	300
Unrecognized tax benefits, penalties and interest			(100)	$ 500	100
Reduction in unrecognized tax benefit from the expiration of statue of limitations and the resolution of tax audits			$ 600
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Tax effects					$ 5,000

INCOME TAXES (Unrecognized Tax Benefits) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits at beginning of year	$ 5,121	$ 1,738	$ 2,064
Additions to current year tax positions	0	1,457	0
Reductions to prior year tax positions	(625)
Additions to prior year tax positions		2,031	0
Expirations	(1,115)	(231)	(533)
Foreign currency translation	(222)	126	207
Unrecognized tax benefits at end of year	$ 3,159	$ 5,121	$ 1,738

EARNINGS (LOSS) PER SHARE (Reconciliation of Basic and Diluted Earnings Per Share Computations) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator for basic and diluted (loss) earnings per share:
Net income (loss)	$ 16,431	$ 31,089	$ 30,747	$ (12,631)	$ 84,194	$ 12,058	$ 25,880	$ (21,393)	$ 65,636	$ 100,739	$ (39,873)
Denominator:
Weighted basic shares outstanding (in shares)									56,148	57,072	57,532
Dilutive effect of equity-based compensation awards (in shares)									192	128	0
Weighted dilutive shares outstanding (in shares)									56,340	57,200	57,532
Basic earnings (loss) per share (in dollars per share)									$ 1.17	$ 1.77	$ (0.69)
Diluted earnings (loss) per share (in dollars per share)									$ 1.16	$ 1.76	$ (0.69)

- Definition

The amount of net income (loss) from continuing operations per each share of common stock or unit outstanding during the reporting period.

+ References

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+ Details

- Definition

The amount of net income (loss) derived from continuing operations during the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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+ Details

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

EARNINGS (LOSS) PER SHARE (Anti-Dilutive Securities) (Details) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restricted Stock and Performance Stock Awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	79,390	152,831	730,929
Restricted Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	121,803	49,373

STOCKHOLDERS' EQUITY (Details) - USD ($) shares in Thousands	12 Months Ended			14 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Oct. 30, 2017
Class of Stock [Line Items]
Repurchases of common stock	$ 45,080,000	$ 48,971,000	$ 22,188,000
Common Stock
Class of Stock [Line Items]
Stock repurchase program, authorized amount					$ 600,000,000
Repurchase of common stock (in shares)	814	907	453	5,600
Repurchases of common stock	$ 8,000	$ 9,000	$ 4,000	$ 293,900,000
Stock repurchase program, remaining authorized repurchase amount	306,100,000			$ 306,100,000
Additional Paid-in Capital
Class of Stock [Line Items]
Repurchases of common stock	$ 45,072,000	$ 48,962,000	$ 22,184,000

ACCUMULATED OTHER COMPREHENSIVE LOSS (Components of AOCI) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Increase (Decrease) in Equity
Beginning balance	$ 1,188,202	$ 1,084,241	$ 1,096,282
Other comprehensive income (loss) before reclassifications	(56,647)	41,966	23,648
Amounts reclassified out of accumulated other comprehensive loss	806	222	0
Tax benefit (loss)	4,877	(269)	16,918
Other comprehensive income (loss)	(50,964)	41,919	40,566
Ending balance	1,169,756	1,188,202	1,084,241
Foreign Currency Translation Adjustments
Increase (Decrease) in Equity
Beginning balance	(170,575)	(212,211)	(252,939)
Other comprehensive income (loss) before reclassifications	(47,374)	41,636	23,967
Amounts reclassified out of accumulated other comprehensive loss	0	0	0
Tax benefit (loss)	5,024	0	16,761
Other comprehensive income (loss)	(42,350)	41,636	40,728
Ending balance	(212,925)	(170,575)	(212,211)
Unrealized (Losses) Gains on Available-for-Sale Securities
Increase (Decrease) in Equity
Beginning balance	(146)	(321)	0
Other comprehensive income (loss) before reclassifications	182	184	(535)
Amounts reclassified out of accumulated other comprehensive loss	0	222	0
Tax benefit (loss)	(105)	(231)	214
Other comprehensive income (loss)	77	175	(321)
Ending balance	(69)	(146)	(321)
Unrealized Loss on Interest Rate Hedge
Increase (Decrease) in Equity
Beginning balance	0	0	0
Other comprehensive income (loss) before reclassifications	(9,579)	0	0
Amounts reclassified out of accumulated other comprehensive loss	806	0	0
Tax benefit (loss)	0	0	0
Other comprehensive income (loss)	(8,773)	0	0
Ending balance	(8,773)	0	0
Unfunded Pension Liability
Increase (Decrease) in Equity
Beginning balance	(1,686)	(1,794)	(1,953)
Other comprehensive income (loss) before reclassifications	124	146	216
Amounts reclassified out of accumulated other comprehensive loss	0	0	0
Tax benefit (loss)	(42)	(38)	(57)
Other comprehensive income (loss)	82	108	159
Ending balance	(1,604)	(1,686)	(1,794)
Accumulated Other Comprehensive loss
Increase (Decrease) in Equity
Beginning balance	(172,407)	(214,326)	(254,892)
Other comprehensive income (loss)	(50,964)	41,919	40,566
Ending balance	$ (223,371)	$ (172,407)	$ (214,326)

STOCK-BASED COMPENSATION AND EMPLOYEE BENEFIT PLANS (Stock-Based Compensation) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 16.8	$ 13.1	$ 10.5
Restricted Stock \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period (in years)	3 years
Restricted Stock \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period (in years)	5 years
2010 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized (in shares)				6,000,000
Vested in 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total income tax benefit from stock-based compensation	$ 3.2
Vested in 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total income tax benefit from stock-based compensation		$ 3.7
Vested in 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total income tax benefit from stock-based compensation			$ 2.8

STOCK-BASED COMPENSATION AND EMPLOYEE BENEFIT PLANS (Restricted Stock Awards) (Details) - Restricted Stock - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Number of Shares
Unvested, beginning of period (in shares)	604,933
Granted (in shares)	327,466
Vested (in shares)	(198,673)
Forfeited (in shares)	(76,486)
Unvested, end of period (in shares)	657,240	604,933
Weighted Average Grant-Date Fair Value
Unvested, beginning of period (in dollars per share)	$ 54.23
Granted (in dollars per share)	55.02
Vested (in dollars per share)	54.22
Forfeited (in dollars per share)	54.00
Unvested, end of period (in dollars per share)	$ 54.65	$ 54.23
Total unrecognized compensation cost	$ 24.9
Expected to be recognized over a weighted average period	2 years 220 days
Total fair value, vested in period	$ 10.8	$ 7.3	$ 8.3
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period (in years)	3 years
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period (in years)	5 years

STOCK-BASED COMPENSATION AND EMPLOYEE BENEFIT PLANS (Performance Stock Awards) (Details) - Performance Stock Awards - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance evaluation stock-based compensation	2 years
Number of Shares
Unvested, beginning of period (in shares)	190,129
Granted (in shares)	171,584
Vested (in shares)	(21,416)
Forfeited (in shares)	(126,807)
Unvested, end of period (in shares)	213,490	190,129
Weighted Average Grant-Date Fair Value
Unvested, beginning of period (in dollars per share)	$ 55.63
Granted (in dollars per share)	55.71
Forfeited (in dollars per share)	53.59
Vested (in dollars per share)	54.82
Unvested, end of period (in dollars per share)	$ 55.71	$ 55.63
Total unrecognized compensation cost	$ 3.2
Total fair value, vested in period	$ 1.2	$ 3.0	$ 1.0

COMMITMENTS AND CONTINGENCIES (Legal and Administrative Proceedings) (Details) $ in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) proceeding claim	Dec. 31, 2012 CAD ($)	Dec. 31, 1999 municipality	Dec. 31, 1968 permit	Dec. 31, 2017 USD ($) proceeding
Legal and Administrative Proceedings
Reserves	$ 25.4				$ 19.3
Safety-Kleen
Legal and Administrative Proceedings
Number of proceedings \| proceeding	67
Loss contingency, claims settled and dismissed, claims \| claim	10
Legal and Administrative Proceedings
Legal and Administrative Proceedings
Reserves	$ 17.9
Possible increase in legal and administrative proceedings	1.8
Ville Mercier
Legal and Administrative Proceedings
Number of permits issued by government, for dumping organic liquid \| permit				2
Number of neighboring municipalities filing separate legal proceedings against the Mercier subsidiary and the government of Quebec \| municipality			3
General damages sought		$ 2.9
Punitive damages sought		$ 10.0
Federal, State, and Provincial Enforcement Actions
Legal and Administrative Proceedings
Reserves relating to legal and administrative proceedings	$ 7.5				$ 1.4
Number of proceedings \| proceeding	10				5

COMMITMENTS AND CONTINGENCIES (Superfund Proceedings) (Details)	12 Months Ended
	Dec. 31, 2018 USD ($) site
Superfund Proceedings
Number of sites owned by the entity subject to proceedings under federal or state superfund laws	128
Superfund Proceedings
Superfund Proceedings
Number of sites subject to proceedings under federal or state superfund laws	128
Number of sites owned by the entity subject to proceedings under federal or state superfund laws	5
Number of sites owned by third parties subject to proceedings under federal or state superfund laws	123
Number of sites for which environmental remediation expense is settled	30
Third party sites requiring expenditure on remediation	16
Number of sites for which environmental remediation expense is not required	77
Possible increase in legal and administrative proceedings \| $	$ 100,000
Number of sites which potential liability could exceed $100,000	12
Notices received from owners of third party sites seeking indemnification from the company	6
Certain other third party sites
Superfund Proceedings
Indemnification agreement with third party sites, sites	11
Safety-Kleen
Superfund Proceedings
Notices received from owners of third party sites seeking indemnification from the company	17

COMMITMENTS AND CONTINGENCIES (Federal, State and Provincial Enforcement Actions) (Details) - Federal, State, and Provincial Enforcement Actions	Dec. 31, 2018 USD ($) proceeding	Dec. 31, 2017 proceeding
Federal and State Enforcement Actions
Number of proceedings \| proceeding	10	5
Sanctions relating to waste treatment \| $	$ 100,000,000

COMMITMENTS AND CONTINGENCIES (Leases) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Lease terms range minimum	1 year
Lease terms range maximum	25 years
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2019	$ 56,480
2020	45,467
2021	33,564
2022	24,509
2023	15,253
Thereafter	35,778
Total minimum lease payments	211,051
Operating leases, rent expense, net	$ 141,100	$ 125,400	$ 121,900

COMMITMENTS AND CONTINGENCIES (Other Contingencies) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Product Liability Contingency [Line Items]
Retention for environmental impairment	$ 1,000
Self-insurance liabilities	$ 53,900	$ 47,900
Weighted average risk free discount rate for self insurance liabilities	2.96%	1.87%
Self Insurance Losses Expected [Abstract]
2019	$ 20,171
2020	12,799
2021	7,964
2022	4,992
2023	4,082
Thereafter	6,385
Undiscounted self-insurance liabilities	56,393
Less: Discount	2,492
Total self-insurance liabilities (included in accrued expenses)	53,901
Minimum
Product Liability Contingency [Line Items]
Deductible health insurance policy	700
Safety-Kleen
Product Liability Contingency [Line Items]
Deductible per occurrence for workers compensation	1,000
Deductible per occurrence for general liability	2,000
Deductible per occurrence for vehicle liability	$ 2,000

SEGMENT REPORTING (Segment Information, Revenues, EBITA, and Reconciliation to the Consolidated Statement of Operations) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Total revenues	$ 858,204	$ 843,181	$ 849,140	$ 749,778	$ 747,403	$ 755,846	$ 752,788	$ 688,941	$ 3,300,303	$ 2,944,978	$ 2,755,226
Adjusted EBITDA									491,005	425,657	400,354
Reconciliation to Consolidated Statements of Operations:
Accretion of environmental liabilities									9,806	9,460	10,177
Depreciation and amortization									298,625	288,422	287,002
Goodwill impairment charge									0	0	34,013
(Loss) income from operations	41,485	65,745	64,353	10,991	27,935	47,663	46,744	5,433	182,574	127,775	69,162
Other expense (income), net	4,061	996	$ (846)	$ 299	3,305	432	833	$ 1,549	4,510	6,119	(6,195)
Loss on early extinguishment of debt		$ 2,500				$ 1,900	6,000		2,488	7,891	0
Gain on sale of businesses							$ (31,700)		0	(30,732)	(16,884)
Interest expense, net of interest income									81,094	85,808	83,525
(Loss) income before (benefit) provision for income taxes									94,482	58,689	8,716
Assets	3,738,321				3,706,570				3,738,321	3,706,570
Property, plant and equipment, net	1,561,978				1,587,365				1,561,978	1,587,365
Goodwill	514,189				478,523				514,189	478,523	465,154
Permits and other intangibles, net	441,875				469,128				441,875	469,128
Permits and other intangibles, net	956,064				947,651				956,064	947,651
Environmental Services
Segment Reporting Information [Line Items]
Total revenues									2,003,843	1,728,700	1,641,432
Reconciliation to Consolidated Statements of Operations:
Goodwill	207,019				172,386				207,019	172,386	169,084
Safety-Kleen
Segment Reporting Information [Line Items]
Total revenues									1,295,355	1,213,703	1,110,727
Reconciliation to Consolidated Statements of Operations:
Goodwill	307,170				306,137				307,170	306,137	296,070
Corporate Items
Segment Reporting Information [Line Items]
Total revenues									1,105	2,575	3,067
Direct revenues
Segment Reporting Information [Line Items]
Total revenues									3,300,303	2,944,978	2,755,226
Direct revenues \| Environmental Services
Segment Reporting Information [Line Items]
Total revenues									2,141,194	1,857,474	1,758,833
Adjusted EBITDA									380,856	321,310	319,075
Reconciliation to Consolidated Statements of Operations:
Assets	1,640,706				1,541,241				1,640,706	1,541,241
Property, plant and equipment, net	951,867				927,139				951,867	927,139
Goodwill	207,019				172,386				207,019	172,386
Permits and other intangibles, net	93,313				97,519				93,313	97,519
Permits and other intangibles, net	300,332				269,905				300,332	269,905
Direct revenues \| Safety-Kleen
Segment Reporting Information [Line Items]
Total revenues									1,161,282	1,087,886	996,083
Adjusted EBITDA									282,029	249,811	219,546
Reconciliation to Consolidated Statements of Operations:
Assets	1,431,381				1,471,291				1,431,381	1,471,291
Property, plant and equipment, net	553,220				582,162				553,220	582,162
Goodwill	307,170				306,137				307,170	306,137
Permits and other intangibles, net	348,562				371,609				348,562	371,609
Permits and other intangibles, net	655,732				677,746				655,732	677,746
Direct revenues \| Corporate Items
Segment Reporting Information [Line Items]
Total revenues									(2,173)	(382)	310
Intersegment revenues, net \| Environmental Services
Segment Reporting Information [Line Items]
Total revenues									134,104	125,822	115,013
Intersegment revenues, net \| Safety-Kleen
Segment Reporting Information [Line Items]
Total revenues									(134,104)	(125,822)	(115,013)
Corporate
Segment Reporting Information [Line Items]
Adjusted EBITDA									(171,880)	(145,464)	(138,267)
Reconciliation to Consolidated Statements of Operations:
Assets	666,234				694,038				666,234	694,038
Property, plant and equipment, net	$ 56,891				$ 78,064				56,891	78,064
Corporate \| Environmental Services
Segment Reporting Information [Line Items]
Total revenues									3,247	2,952	2,388
Corporate \| Safety-Kleen
Segment Reporting Information [Line Items]
Total revenues									31	5	369
Corporate \| Corporate Items
Segment Reporting Information [Line Items]
Total revenues									$ (3,278)	$ (2,957)	$ (2,757)

SEGMENT REPORTING (Geographical Information) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Revenues	$ 858,204	$ 843,181	$ 849,140	$ 749,778	$ 747,403	$ 755,846	$ 752,788	$ 688,941	$ 3,300,303	$ 2,944,978	$ 2,755,226
Percent of revenues									100.00%	100.00%	100.00%
Property, plant and equipment, net	$ 1,561,978				$ 1,587,365				$ 1,561,978	$ 1,587,365
Percent of property, plant and equipment, net	100.00%				100.00%				100.00%	100.00%
Permits and other intangibles, net	$ 441,875				$ 469,128				$ 441,875	$ 469,128
Percent of permits and other intangibles, net	100.00%				100.00%				100.00%	100.00%
Assets	$ 3,738,321				$ 3,706,570				$ 3,738,321	$ 3,706,570
United States
Segment Reporting Information [Line Items]
Revenues									2,796,145
Property, plant and equipment, net	$ 1,233,949				$ 1,175,437				$ 1,233,949	$ 1,175,437
Percent of property, plant and equipment, net	79.00%				74.00%				79.00%	74.00%
Permits and other intangibles, net	$ 393,045				$ 408,654				$ 393,045	$ 408,654
Percent of permits and other intangibles, net	88.90%				87.10%				88.90%	87.10%
Assets	$ 3,090,311				$ 2,985,394				$ 3,090,311	$ 2,985,394
Canada
Segment Reporting Information [Line Items]
Revenues									504,158
Property, plant and equipment, net	$ 328,029				$ 411,928				$ 328,029	$ 411,928
Percent of property, plant and equipment, net	21.00%				26.00%				21.00%	26.00%
Permits and other intangibles, net	$ 48,830				$ 60,474				$ 48,830	$ 60,474
Percent of permits and other intangibles, net	11.10%				12.90%				11.10%	12.90%
Assets	$ 648,010				$ 721,176				$ 648,010	$ 721,176
Direct revenues
Segment Reporting Information [Line Items]
Revenues									3,300,303	2,944,978	$ 2,755,226
Direct revenues \| United States
Segment Reporting Information [Line Items]
Revenues									$ 2,721,814	$ 2,392,000	$ 2,213,355
Percent of revenues									82.50%	81.20%	80.30%
Direct revenues \| Canada
Segment Reporting Information [Line Items]
Revenues									$ 578,489	$ 552,978	$ 541,871
Percent of revenues									17.50%	18.80%	19.70%

GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Balance Sheet) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Assets:
Cash and cash equivalents	$ 226,507	$ 319,399	$ 306,997	$ 184,708
Short-term marketable securities	52,856	38,179
Intercompany receivables	0	0
Accounts receivable, net	606,952	528,924
Other current assets	315,843	267,554
Property, plant and equipment, net	1,561,978	1,587,365
Investments in subsidiaries	0	0
Intercompany debt receivable	0	0
Goodwill	514,189	478,523	465,154
Permits and other intangibles, net	441,875	469,128
Other long-term assets	18,121	17,498
Total assets	3,738,321	3,706,570
Liabilities and Stockholders' Equity:
Current liabilities	602,278	503,817
Intercompany payables	0	0
Closure, post-closure and remedial liabilities, net	167,914	165,723
Long-term obligations, less current portion	1,565,021	1,625,537
Intercompany debt payable	0	0
Other long-term liabilities	233,352	223,291
Total liabilities	2,568,565	2,518,368
Stockholders' equity	1,169,756	1,188,202	1,084,241	1,096,282
Total liabilities and stockholders' equity	3,738,321	3,706,570
Reportable Legal Entities \| Clean Harbors, Inc.
Assets:
Cash and cash equivalents	27,308	51,638	51,417	11,017
Short-term marketable securities	67	0
Intercompany receivables	262,475	238,339
Accounts receivable, net	0	0
Other current assets	0	897
Property, plant and equipment, net	0	0
Investments in subsidiaries	3,162,704	3,112,547
Intercompany debt receivable	0	0
Goodwill	0	0
Permits and other intangibles, net	0	0
Other long-term assets	1,551	2,084
Total assets	3,454,105	3,405,505
Liabilities and Stockholders' Equity:
Current liabilities	20,170	16,954
Intercompany payables	699,158	574,812
Closure, post-closure and remedial liabilities, net	0	0
Long-term obligations, less current portion	1,565,021	1,625,537
Intercompany debt payable	0	0
Other long-term liabilities	0	0
Total liabilities	2,284,349	2,217,303
Stockholders' equity	1,169,756	1,188,202
Total liabilities and stockholders' equity	3,454,105	3,405,505
Reportable Legal Entities \| Guarantor Subsidiaries
Assets:
Cash and cash equivalents	101,302	207,777	155,943	83,479
Short-term marketable securities	0	0
Intercompany receivables	721,521	590,100
Accounts receivable, net	520,785	433,042
Other current assets	289,869	233,602
Property, plant and equipment, net	1,233,578	1,174,975
Investments in subsidiaries	571,304	569,568
Intercompany debt receivable	14,669	92,530
Goodwill	456,307	415,641
Permits and other intangibles, net	393,045	408,655
Other long-term assets	13,545	12,064
Total assets	4,315,925	4,137,954
Liabilities and Stockholders' Equity:
Current liabilities	457,164	371,135
Intercompany payables	321,846	289,531
Closure, post-closure and remedial liabilities, net	151,480	148,872
Long-term obligations, less current portion	0	0
Intercompany debt payable	21,000	21,000
Other long-term liabilities	212,924	201,086
Total liabilities	1,164,414	1,031,624
Stockholders' equity	3,151,511	3,106,330
Total liabilities and stockholders' equity	4,315,925	4,137,954
Reportable Legal Entities \| Non-Guarantor Subsidiaries
Assets:
Cash and cash equivalents	97,897	59,984	99,637	90,212
Short-term marketable securities	52,789	38,179
Intercompany receivables	60,693	52,909
Accounts receivable, net	86,167	95,882
Other current assets	49,631	52,947
Property, plant and equipment, net	328,400	412,390
Investments in subsidiaries	0	0
Intercompany debt receivable	21,000	21,000
Goodwill	57,882	62,882
Permits and other intangibles, net	48,830	60,473
Other long-term assets	3,025	3,350
Total assets	806,314	859,996
Liabilities and Stockholders' Equity:
Current liabilities	148,601	135,620
Intercompany payables	23,685	17,005
Closure, post-closure and remedial liabilities, net	16,434	16,851
Long-term obligations, less current portion	0	0
Intercompany debt payable	14,669	92,530
Other long-term liabilities	20,428	22,205
Total liabilities	223,817	284,211
Stockholders' equity	582,497	575,785
Total liabilities and stockholders' equity	806,314	859,996
Consolidating Adjustments
Assets:
Cash and cash equivalents	0	0	$ 0	$ 0
Short-term marketable securities	0	0
Intercompany receivables	(1,044,689)	(881,348)
Accounts receivable, net	0	0
Other current assets	(23,657)	(19,892)
Property, plant and equipment, net	0	0
Investments in subsidiaries	(3,734,008)	(3,682,115)
Intercompany debt receivable	(35,669)	(113,530)
Goodwill	0	0
Permits and other intangibles, net	0	0
Other long-term assets	0	0
Total assets	(4,838,023)	(4,696,885)
Liabilities and Stockholders' Equity:
Current liabilities	(23,657)	(19,892)
Intercompany payables	(1,044,689)	(881,348)
Closure, post-closure and remedial liabilities, net	0	0
Long-term obligations, less current portion	0	0
Intercompany debt payable	(35,669)	(113,530)
Other long-term liabilities	0	0
Total liabilities	(1,104,015)	(1,014,770)
Stockholders' equity	(3,734,008)	(3,682,115)
Total liabilities and stockholders' equity	$ (4,838,023)	$ (4,696,885)

GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Income Statement) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues
Total revenues	$ 858,204	$ 843,181	$ 849,140	$ 749,778	$ 747,403	$ 755,846	$ 752,788	$ 688,941	$ 3,300,303	$ 2,944,978	$ 2,755,226
Cost of revenues (exclusive of items shown separately below)
Total cost of revenues	594,857	580,685	583,584	546,425	526,690	519,595	519,803	496,585	2,305,551	2,062,673	1,932,857
Selling, general and administrative expenses									503,747	456,648	422,015
Accretion of environmental liabilities									9,806	9,460	10,177
Depreciation and amortization									298,625	288,422	287,002
Goodwill impairment charge									0	0	34,013
(Loss) income from operations	41,485	65,745	64,353	10,991	27,935	47,663	46,744	5,433	182,574	127,775	69,162
Other (expense) income, net	(4,061)	(996)	846	(299)	(3,305)	(432)	(833)	(1,549)	(4,510)	(6,119)	6,195
Loss on early extinguishment of debt		(2,500)				(1,900)	(6,000)		(2,488)	(7,891)	0
Gain on sale of businesses							31,700		0	30,732	16,884
Interest (expense) income, net									(81,094)	(85,808)	(83,525)
Equity in earnings of subsidiaries, net of tax									0	0	0
Intercompany interest income (expense)									0	0	0
(Loss) income before (benefit) provision for income taxes									94,482	58,689	8,716
(Benefit) provision for income taxes									28,846	(42,050)	48,589
Net income (loss)	$ 16,431	$ 31,089	$ 30,747	$ (12,631)	$ 84,194	$ 12,058	$ 25,880	$ (21,393)	65,636	100,739	(39,873)
Other comprehensive loss									(50,964)	41,919	40,566
Comprehensive income (loss)									14,672	142,658	693
Reportable Legal Entities \| Clean Harbors, Inc.
Revenues
Total revenues									0	0	0
Cost of revenues (exclusive of items shown separately below)
Total cost of revenues									0	0	0
Selling, general and administrative expenses									347	0	85
Accretion of environmental liabilities									0	0	0
Depreciation and amortization									0	0	0
Goodwill impairment charge											0
(Loss) income from operations									(347)	0	(85)
Other (expense) income, net									(1,384)	(222)	0
Loss on early extinguishment of debt									(2,488)	(7,891)
Gain on sale of businesses										0	0
Interest (expense) income, net									(83,362)	(87,113)	(88,984)
Equity in earnings of subsidiaries, net of tax									129,082	157,963	13,568
Intercompany interest income (expense)									0	0	0
(Loss) income before (benefit) provision for income taxes									41,501	62,737	(75,501)
(Benefit) provision for income taxes									(24,135)	(38,002)	(35,628)
Net income (loss)									65,636	100,739	(39,873)
Other comprehensive loss									(50,964)	41,919	40,566
Comprehensive income (loss)									14,672	142,658	693
Reportable Legal Entities \| Guarantor Subsidiaries
Revenues
Total revenues									2,682,710	2,362,292	2,158,853
Cost of revenues (exclusive of items shown separately below)
Total cost of revenues									1,841,070	1,610,781	1,465,201
Selling, general and administrative expenses									419,984	373,050	341,963
Accretion of environmental liabilities									8,797	8,479	9,261
Depreciation and amortization									219,530	205,034	201,153
Goodwill impairment charge											0
(Loss) income from operations									193,329	164,948	141,275
Other (expense) income, net									(1,284)	(5,156)	7,713
Loss on early extinguishment of debt									0	0
Gain on sale of businesses										30,732	1,704
Interest (expense) income, net									1,252	1,523	5,391
Equity in earnings of subsidiaries, net of tax									(25,765)	(48,683)	(80,244)
Intercompany interest income (expense)									2,841	5,288	19,855
(Loss) income before (benefit) provision for income taxes									170,373	148,652	95,694
(Benefit) provision for income taxes									46,267	(10,117)	82,643
Net income (loss)									124,106	158,769	13,051
Other comprehensive loss									(50,964)	41,919	40,566
Comprehensive income (loss)									73,142	200,688	53,617
Reportable Legal Entities \| Non-Guarantor Subsidiaries
Revenues
Total revenues									687,645	648,553	655,868
Cost of revenues (exclusive of items shown separately below)
Total cost of revenues									534,533	517,759	527,151
Selling, general and administrative expenses									83,416	83,598	79,967
Accretion of environmental liabilities									1,009	981	916
Depreciation and amortization									79,095	83,388	85,849
Goodwill impairment charge											34,013
(Loss) income from operations									(10,408)	(37,173)	(72,028)
Other (expense) income, net									(1,842)	(741)	(1,518)
Loss on early extinguishment of debt									0	0
Gain on sale of businesses										0	15,180
Interest (expense) income, net									1,016	(218)	68
Equity in earnings of subsidiaries, net of tax									0	0	0
Intercompany interest income (expense)									(2,841)	(5,288)	(19,855)
(Loss) income before (benefit) provision for income taxes									(14,075)	(43,420)	(78,153)
(Benefit) provision for income taxes									6,714	6,069	1,574
Net income (loss)									(20,789)	(49,489)	(79,727)
Other comprehensive loss									(44,292)	38,131	15,291
Comprehensive income (loss)									(65,081)	(11,358)	(64,436)
Consolidating Adjustments
Revenues
Total revenues									(70,052)	(65,867)	(59,495)
Cost of revenues (exclusive of items shown separately below)
Total cost of revenues									(70,052)	(65,867)	(59,495)
Selling, general and administrative expenses									0	0	0
Accretion of environmental liabilities									0	0	0
Depreciation and amortization									0	0	0
Goodwill impairment charge											0
(Loss) income from operations									0	0	0
Other (expense) income, net									0	0	0
Loss on early extinguishment of debt									0	0
Gain on sale of businesses										0	0
Interest (expense) income, net									0	0	0
Equity in earnings of subsidiaries, net of tax									(103,317)	(109,280)	66,676
Intercompany interest income (expense)									0	0	0
(Loss) income before (benefit) provision for income taxes									(103,317)	(109,280)	66,676
(Benefit) provision for income taxes									0	0	0
Net income (loss)									(103,317)	(109,280)	66,676
Other comprehensive loss									95,256	(80,050)	(55,857)
Comprehensive income (loss)									(8,061)	(189,330)	10,819
Service revenues
Revenues
Total revenues									2,709,239	2,398,650	2,280,809
Cost of revenues (exclusive of items shown separately below)
Total cost of revenues									1,861,975	1,641,798	1,543,210
Service revenues \| Reportable Legal Entities \| Clean Harbors, Inc.
Revenues
Total revenues									0	0	0
Cost of revenues (exclusive of items shown separately below)
Total cost of revenues									0	0	0
Service revenues \| Reportable Legal Entities \| Guarantor Subsidiaries
Revenues
Total revenues									2,145,310	1,870,256	1,747,985
Cost of revenues (exclusive of items shown separately below)
Total cost of revenues									1,421,693	1,224,326	1,116,132
Service revenues \| Reportable Legal Entities \| Non-Guarantor Subsidiaries
Revenues
Total revenues									621,435	582,042	582,075
Cost of revenues (exclusive of items shown separately below)
Total cost of revenues									497,788	471,120	476,329
Service revenues \| Consolidating Adjustments
Revenues
Total revenues									(57,506)	(53,648)	(49,251)
Cost of revenues (exclusive of items shown separately below)
Total cost of revenues									(57,506)	(53,648)	(49,251)
Product revenues
Revenues
Total revenues									591,064	546,328	474,417
Cost of revenues (exclusive of items shown separately below)
Total cost of revenues									443,576	420,875	389,647
Product revenues \| Reportable Legal Entities \| Clean Harbors, Inc.
Revenues
Total revenues									0	0	0
Cost of revenues (exclusive of items shown separately below)
Total cost of revenues									0	0	0
Product revenues \| Reportable Legal Entities \| Guarantor Subsidiaries
Revenues
Total revenues									537,400	492,036	410,868
Cost of revenues (exclusive of items shown separately below)
Total cost of revenues									419,377	386,455	349,069
Product revenues \| Reportable Legal Entities \| Non-Guarantor Subsidiaries
Revenues
Total revenues									66,210	66,511	73,793
Cost of revenues (exclusive of items shown separately below)
Total cost of revenues									36,745	46,639	50,822
Product revenues \| Consolidating Adjustments
Revenues
Total revenues									(12,546)	(12,219)	(10,244)
Cost of revenues (exclusive of items shown separately below)
Total cost of revenues									$ (12,546)	$ (12,219)	$ (10,244)

GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Cash Flows) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed consolidating statement of cash flows
Net cash from operating activities	$ 373,210	$ 285,698	$ 259,624
Cash flows used in investing activities:
Additions to property, plant and equipment	(193,344)	(167,007)	(219,384)
Proceeds from sale and disposal of fixed assets	15,445	7,124	20,817
Proceeds from sale of available-for-sale securities	28,723	376
Acquisitions, net of cash acquired	(151,023)	(49,227)	(206,915)
Proceeds from sale of businesses, net of transactional costs	0	45,426	47,134
Additions to intangible assets including costs to obtain or renew permits	(4,688)	(1,617)	(2,831)
Purchases of available-for-sale securities	(44,772)	(38,342)	(598)
Intercompany	0	0	0
Intercompany debt		0	0
Investment in subsidiaries			0
Net cash used in investing activities	(349,659)	(203,267)	(361,777)
Cash flows (used in) from financing activities:
Change in uncashed checks	132	(5,940)	(3,177)
Proceeds from exercise of stock options	0	46	627
Tax payments related to withholdings on vested restricted stock	(3,266)	(3,149)	(2,819)
Excess tax benefit of stock-based compensation	0	0	1,198
Deferred financing costs paid	(4,027)	(5,718)	(4,031)
Repurchases of common stock	(45,080)	(48,971)	(22,188)
Principal payments on debt	(405,768)	(402,000)	0
Premiums paid on early extinguishment of debt	(1,238)	(6,028)	0
Issuance of senior secured notes, net of discount	348,250	399,000	0
Issuance of senior secured notes, net of discount	0	0	250,625
Borrowing from revolving credit facility	50,000	0	0
Payment on revolving credit facility	(50,000)	0	0
Intercompany	0	0	0
Intercompany debt		0	0
Net cash (used in) from financing activities	(110,997)	(72,760)	220,235
Effect of exchange rate change on cash	(5,446)	2,731	4,207
(Decrease) increase in cash and cash equivalents	(92,892)	12,402	122,289
Cash and cash equivalents, beginning of year	319,399	306,997	184,708
Cash and cash equivalents, end of year	226,507	319,399	306,997
Guarantor Subsidiaries
Cash flows used in investing activities:
Proceeds from sale of available-for-sale securities	0
Reportable Legal Entities \| Clean Harbors, Inc.
Condensed consolidating statement of cash flows
Net cash from operating activities	34,135	16,292	51,033
Cash flows used in investing activities:
Additions to property, plant and equipment	0	0	0
Proceeds from sale and disposal of fixed assets	0	0	0
Proceeds from sale of available-for-sale securities	0	376
Acquisitions, net of cash acquired	0	0	0
Proceeds from sale of businesses, net of transactional costs		0	0
Additions to intangible assets including costs to obtain or renew permits	0	0	0
Purchases of available-for-sale securities	(1,450)	0	(102)
Intercompany	0	0	0
Intercompany debt		0	0
Investment in subsidiaries			(257,125)
Net cash used in investing activities	(1,450)	376	(257,227)
Cash flows (used in) from financing activities:
Change in uncashed checks	0	0	0
Proceeds from exercise of stock options		46	627
Tax payments related to withholdings on vested restricted stock	(3,266)	(3,149)	(2,819)
Excess tax benefit of stock-based compensation			1,198
Deferred financing costs paid	(4,027)	(5,718)	(4,031)
Repurchases of common stock	(45,080)	(48,971)	(22,188)
Principal payments on debt	(405,768)	(402,000)
Premiums paid on early extinguishment of debt	(1,238)	(6,028)
Issuance of senior secured notes, net of discount	348,250	399,000
Issuance of senior secured notes, net of discount			250,625
Borrowing from revolving credit facility	50,000
Payment on revolving credit facility	(50,000)
Intercompany	54,114	54,074	23,182
Intercompany debt		(3,701)	0
Net cash (used in) from financing activities	(57,015)	(16,447)	246,594
Effect of exchange rate change on cash	0	0	0
(Decrease) increase in cash and cash equivalents	(24,330)	221	40,400
Cash and cash equivalents, beginning of year	51,638	51,417	11,017
Cash and cash equivalents, end of year	27,308	51,638	51,417
Reportable Legal Entities \| Guarantor Subsidiaries
Condensed consolidating statement of cash flows
Net cash from operating activities	260,101	217,001	125,591
Cash flows used in investing activities:
Additions to property, plant and equipment	(161,342)	(142,211)	(194,184)
Proceeds from sale and disposal of fixed assets	4,174	1,979	12,926
Proceeds from sale of available-for-sale securities		0
Acquisitions, net of cash acquired	(151,023)	(11,427)	(196,915)
Proceeds from sale of businesses, net of transactional costs		45,245	18,885
Additions to intangible assets including costs to obtain or renew permits	(4,326)	(1,153)	(1,749)
Purchases of available-for-sale securities	0	0	0
Intercompany	(54,114)	(54,074)	(23,182)
Intercompany debt		0	63,118
Investment in subsidiaries			0
Net cash used in investing activities	(366,631)	(161,641)	(321,101)
Cash flows (used in) from financing activities:
Change in uncashed checks	55	(3,526)	(3,651)
Proceeds from exercise of stock options		0	0
Tax payments related to withholdings on vested restricted stock	0	0	0
Excess tax benefit of stock-based compensation			0
Deferred financing costs paid	0	0	0
Repurchases of common stock	0	0	0
Principal payments on debt	0	0
Premiums paid on early extinguishment of debt	0	0
Issuance of senior secured notes, net of discount	0	0
Issuance of senior secured notes, net of discount			250,625
Borrowing from revolving credit facility	0
Payment on revolving credit facility	0
Intercompany	0	0	0
Intercompany debt		0	21,000
Net cash (used in) from financing activities	55	(3,526)	267,974
Effect of exchange rate change on cash	0	0	0
(Decrease) increase in cash and cash equivalents	(106,475)	51,834	72,464
Cash and cash equivalents, beginning of year	207,777	155,943	83,479
Cash and cash equivalents, end of year	101,302	207,777	155,943
Reportable Legal Entities \| Non-Guarantor Subsidiaries
Condensed consolidating statement of cash flows
Net cash from operating activities	78,974	52,405	83,000
Cash flows used in investing activities:
Additions to property, plant and equipment	(32,002)	(24,796)	(25,200)
Proceeds from sale and disposal of fixed assets	11,271	5,145	7,891
Proceeds from sale of available-for-sale securities	28,723	0
Acquisitions, net of cash acquired	0	(37,800)	(10,000)
Proceeds from sale of businesses, net of transactional costs		181	28,249
Additions to intangible assets including costs to obtain or renew permits	(362)	(464)	(1,082)
Purchases of available-for-sale securities	(43,322)	(38,342)	(496)
Intercompany	0	0	0
Intercompany debt		3,701	(21,000)
Investment in subsidiaries			0
Net cash used in investing activities	(35,692)	(92,375)	(21,638)
Cash flows (used in) from financing activities:
Change in uncashed checks	77	(2,414)	474
Proceeds from exercise of stock options		0	0
Tax payments related to withholdings on vested restricted stock	0	0	0
Excess tax benefit of stock-based compensation			0
Deferred financing costs paid	0	0	0
Repurchases of common stock	0	0	0
Principal payments on debt	0	0
Premiums paid on early extinguishment of debt	0	0
Issuance of senior secured notes, net of discount	0	0
Issuance of senior secured notes, net of discount			0
Borrowing from revolving credit facility	0
Payment on revolving credit facility	0
Intercompany	0	0	6,500
Intercompany debt		0	(63,118)
Net cash (used in) from financing activities	77	(2,414)	(56,144)
Effect of exchange rate change on cash	(5,446)	2,731	4,207
(Decrease) increase in cash and cash equivalents	37,913	(39,653)	9,425
Cash and cash equivalents, beginning of year	59,984	99,637	90,212
Cash and cash equivalents, end of year	97,897	59,984	99,637
Consolidating Adjustments
Condensed consolidating statement of cash flows
Net cash from operating activities	0	0	0
Cash flows used in investing activities:
Additions to property, plant and equipment	0	0	0
Proceeds from sale and disposal of fixed assets	0	0	0
Proceeds from sale of available-for-sale securities	0	0
Acquisitions, net of cash acquired	0	0	0
Proceeds from sale of businesses, net of transactional costs		0	0
Additions to intangible assets including costs to obtain or renew permits	0	0	0
Purchases of available-for-sale securities	0	0	0
Intercompany	54,114	54,074	23,182
Intercompany debt		(3,701)	(42,118)
Investment in subsidiaries			257,125
Net cash used in investing activities	54,114	50,373	238,189
Cash flows (used in) from financing activities:
Change in uncashed checks	0	0	0
Proceeds from exercise of stock options		0	0
Tax payments related to withholdings on vested restricted stock	0	0	0
Excess tax benefit of stock-based compensation			0
Deferred financing costs paid	0	0	0
Repurchases of common stock	0	0	0
Principal payments on debt	0	0
Premiums paid on early extinguishment of debt	0	0
Issuance of senior secured notes, net of discount	0	0
Issuance of senior secured notes, net of discount			(250,625)
Borrowing from revolving credit facility	0
Payment on revolving credit facility	0
Intercompany	(54,114)	(54,074)	(29,682)
Intercompany debt		3,701	42,118
Net cash (used in) from financing activities	(54,114)	(50,373)	(238,189)
Effect of exchange rate change on cash	0	0	0
(Decrease) increase in cash and cash equivalents	0	0	0
Cash and cash equivalents, beginning of year	0	0	0
Cash and cash equivalents, end of year	$ 0	$ 0	$ 0

QUARTERLY DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 858,204	$ 843,181	$ 849,140	$ 749,778	$ 747,403	$ 755,846	$ 752,788	$ 688,941	$ 3,300,303	$ 2,944,978	$ 2,755,226
Total cost of revenues	594,857	580,685	583,584	546,425	526,690	519,595	519,803	496,585	2,305,551	2,062,673	1,932,857
(Loss) income from operations	41,485	65,745	64,353	10,991	27,935	47,663	46,744	5,433	182,574	127,775	69,162
Other (expense) income, net	(4,061)	(996)	846	(299)	(3,305)	(432)	(833)	(1,549)	(4,510)	(6,119)	6,195
Net income (loss)	$ 16,431	$ 31,089	$ 30,747	$ (12,631)	$ 84,194	$ 12,058	$ 25,880	$ (21,393)	$ 65,636	$ 100,739	$ (39,873)
Basic (loss) earnings per share (in dollars per share)	$ 0.29	$ 0.55	$ 0.55	$ (0.22)	$ 1.48	$ 0.21	$ 0.45	$ (0.37)	$ 1.17	$ 1.77	$ (0.69)
Diluted (loss) earnings per share (in dollars per share)	$ 0.29	$ 0.55	$ 0.54	$ (0.22)	$ 1.48	$ 0.21	$ 0.45	$ (0.37)	$ 1.16	$ 1.76	$ (0.69)
Gain on sale of businesses							$ 31,700		$ 0	$ 30,732	$ 16,884
Loss on early extinguishment of debt		$ 2,500				$ 1,900	$ 6,000		$ 2,488	7,891	$ 0
Tax benefit due to reduction in net deferred tax liability					$ 93,000					$ 99,900

SCHEDULE II VALUATION AND QUALIFYING ACCOUNTS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for Doubtful Accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance Beginning of Period	$ 16,173	$ 15,046	$ 15,194
Additions Charged to Operating Expense	15,817	7,901	6,907
Deductions from Reserves	5,622	6,774	7,055
Balance End of Period	26,368	16,173	15,046
Revenue Allowance
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance Beginning of Period	11,626	14,203	16,232
Additions Charged to Operating Expense	41,338	24,862	24,252
Deductions from Reserves	35,017	27,439	26,281
Balance End of Period	17,947	11,626	14,203
Valuation Allowance on Deferred Tax Assets
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance Beginning of Period	68,355	55,189	30,916
Additions Charged to Operating Expense	10,466	9,052	22,564
Deductions from Reserves	474	4,114	1,709
Balance End of Period	$ 79,295	$ 68,355	$ 55,189

CONSOLIDATED STATEMENTS OF OPERATIONS (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Interest expense, interest income	$ 2,958	$ 1,897	$ 784

OPERATIONS	12 Months Ended
OPERATIONS	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
OPERATIONS	OPERATIONS Clean Harbors, Inc., through its subsidiaries (collectively, the "Company"), is a leading provider of environmental, energy and industrial services throughout North America. We are also the largest re-refiner and recycler of used oil in the world and the largest provider of parts cleaning and related environmental services to commercial, industrial and automotive customers in North America.

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (PARENTHETICAL) - $ / shares	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Stockholders' Equity [Abstract]
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01	$ 0.01

SIGNIFICANT ACCOUNTING POLICIES (Cash, Cash Equivalents and Uncashed Checks) (Details)	Dec. 31, 2018 USD ($)
Accounting Policies [Abstract]
Bank disbursement account balance	$ 0

SEGMENT REPORTING (Segment Additional Information) (Details)	12 Months Ended
	Dec. 31, 2018 segment
Segment Reporting [Abstract]
Number of operating segments	2

GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Narrative) (Details)	12 Months Ended
	Dec. 31, 2018
Guarantor and Non-Guarantor Subsidiaries Financial Information [Abstract]
Guarantor, ownership interest by Clean Harbors, Inc.	100.00%