0000822818-21-000003 | 10-K | XBRL Viewer

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Cover - USD ($) $ in Billions	12 Months Ended
Cover - USD ($) $ in Billions	Dec. 31, 2020	Feb. 17, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-34223
Entity Registrant Name	CLEAN HARBORS, INC
Entity Incorporation, State or Country Code	MA
Entity Tax Identification Number	04-2997780
Entity Address, Address Line One	42 Longwater Drive
Entity Address, City or Town	Norwell
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02061-9149
City Area Code	781
Local Phone Number	792-5000
Title of 12(b) Security	Common Stock, $0.01 par value
Trading Symbol	CLH
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 3.1
Entity Common Stock, Shares Outstanding		54,796,559
Documents Incorporated by Reference	Certain portions of the registrant's definitive proxy statement for its 2021 annual meeting of stockholders (which will be filed with the Commission not later than April 23, 2021) are incorporated by reference into Part III of this report.
Entity Central Index Key	0000822818
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	false

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 519,101	$ 371,991
Short-term marketable securities	51,857	42,421
Accounts receivable, net of allowances aggregating $44,749 and $38,711, respectively	611,534	644,738
Unbilled accounts receivable	55,681	56,326
Inventories and supplies	220,498	214,744
Prepaid expenses and other current assets	67,051	70,688
Total current assets	1,525,722	1,400,908
Property, plant and equipment, net	1,525,298	1,588,151
Other assets:
Operating lease right-of-use assets	150,341	162,206
Goodwill	527,023	525,013
Permits and other intangibles, net	386,620	419,066
Other	16,516	13,560
Total other assets	1,080,500	1,119,845
Total assets	4,131,520	4,108,904
Current liabilities:
Current portion of long-term debt	7,535	7,535
Accounts payable	195,878	298,375
Deferred revenue	74,066	73,370
Accrued expenses	295,823	276,540
Current portion of closure, post-closure and remedial liabilities	26,093	23,301
Current portion of operating lease liabilities	36,750	40,979
Total current liabilities	636,145	720,100
Other liabilities:
Closure and post-closure liabilities, less current portion of $13,903 and $7,283, respectively	74,023	68,368
Remedial liabilities, less current portion of $12,190 and $16,018, respectively	102,623	98,155
Long-term debt, less current portion	1,549,641	1,554,116
Operating lease liabilities, less current portion	114,258	121,020
Deferred tax liabilities	230,097	231,337
Other long-term liabilities	83,182	45,995
Total other liabilities	2,153,824	2,118,991
Commitments and contingent liabilities (See Note 17)
Stockholders' equity:
Common stock, $.01 par value: Authorized 80,000,000 shares; issued and outstanding — and 55,797,734 shares, respectively	548	558
Additional paid-in capital	582,749	644,412
Accumulated other comprehensive loss	(211,477)	(210,051)
Accumulated earnings	969,731	834,894
Total stockholders' equity	1,341,551	1,269,813
Total liabilities and stockholders' equity	$ 4,131,520	$ 4,108,904

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Account receivable, allowances aggregating	$ 44,749	$ 38,711
Closure and post-closure liabilities, current portion	13,903	7,283
Remedial liabilities, current portion	$ 12,190	$ 16,018
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)	54,772,696	55,797,734
Common stock, outstanding shares (in shares)	54,772,696	55,797,734

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues:
Total revenues	$ 3,144,097	$ 3,412,190	$ 3,300,303
Cost of revenues: (exclusive of items shown separately below)
Total cost of revenues	2,137,751	2,387,819	2,305,551
Selling, general and administrative expenses	451,044	484,054	503,747
Accretion of environmental liabilities	11,051	10,136	9,806
Depreciation and amortization	292,915	300,725	298,625
Income from operations	251,336	229,456	182,574
Other (expense) income, net	(290)	2,897	(4,510)
Loss on early extinguishment of debt	0	(6,131)	(2,488)
(Loss) gain on sale of businesses	(3,376)	687	0
Interest expense, net of interest income of $3,462, $4,227 and $2,958, respectively	(73,120)	(78,670)	(81,094)
Income before provision for income taxes	174,550	148,239	94,482
Provision for income taxes	39,713	50,499	28,846
Net income	$ 134,837	$ 97,740	$ 65,636
Earnings per share:
Basic (in dollars per share)	$ 2.43	$ 1.75	$ 1.17
Diluted (in dollars per share)	$ 2.42	$ 1.74	$ 1.16
Shares used to compute earnings per share — Basic (in shares)	55,479	55,845	56,148
Shares used to compute earnings per share — Diluted (in shares)	55,690	56,129	56,340
Service revenues
Revenues:
Total revenues	$ 2,724,584	$ 2,842,881	$ 2,709,239
Cost of revenues: (exclusive of items shown separately below)
Total cost of revenues	1,786,718	1,945,021	1,861,975
Product revenues
Revenues:
Total revenues	419,513	569,309	591,064
Cost of revenues: (exclusive of items shown separately below)
Total cost of revenues	$ 351,033	$ 442,798	$ 443,576

CONSOLIDATED STATEMENTS OF OPERATIONS (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Interest income	$ 3,462	$ 4,227	$ 2,958

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 134,837	$ 97,740	$ 65,636
Other comprehensive (loss) income, net of tax:
Unrealized (losses) gains on available-for-sale securities	(8)	(120)	77
Reclassification adjustment for losses on available-for-sale securities included in net income	0	332	0
Unrealized loss on interest rate hedge	(20,970)	(14,401)	(9,579)
Reclassification adjustment for losses on interest rate hedge included in net income	8,180	2,335	806
Foreign currency translation adjustments	11,561	25,130	(42,350)
Unrealized (loss) gain on net pension liability	(189)	44	82
Other comprehensive (loss) income, net of tax	(1,426)	13,320	(50,964)
Comprehensive income	$ 133,411	$ 111,060	$ 14,672

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net income	$ 134,837	$ 97,740	$ 65,636
Adjustments to reconcile net income to net cash from operating activities:
Depreciation and amortization	292,915	300,725	298,625
Allowance for doubtful accounts	10,133	2,408	15,817
Amortization of deferred financing costs and debt discount	3,666	3,809	3,846
Accretion of environmental liabilities	11,051	10,136	9,806
Changes in environmental liability estimates	10,698	(332)	2,147
Deferred income taxes	(9,748)	8,005	19,089
Other expense (income), net	290	(2,897)	4,510
Stock-based compensation	18,502	17,816	16,792
Loss (gain) on sale of businesses	3,376	(687)	0
Loss on early extinguishment of debt	0	6,131	2,488
Environmental expenditures	(12,401)	(18,701)	(10,115)
Changes in assets and liabilities, net of acquisitions:
Accounts receivable and unbilled accounts receivable	22,422	(33,271)	(79,563)
Inventories and supplies	(7,933)	(15,869)	(26,958)
Other current and non-current assets	(12,602)	(14,421)	(7,946)
Accounts payable	(80,328)	7,153	46,915
Other current and long-term liabilities	45,719	45,447	12,121
Net cash from operating activities	430,597	413,192	373,210
Cash flows used in investing activities:
Additions to property, plant and equipment	(196,256)	(216,324)	(193,344)
Proceeds from sale and disposal of fixed assets	9,623	11,655	15,445
Acquisitions, net of cash acquired	(8,839)	(29,363)	(151,023)
Additions to intangible assets including costs to obtain or renew permits	(2,029)	(3,904)	(4,688)
Purchases of available-for-sale securities	(70,891)	(35,836)	(44,772)
Proceeds from sale of available-for-sale securities	61,220	51,202	28,723
Proceeds from sale of businesses, net of transactional costs	7,712	4,714	0
Net cash used in investing activities	(199,460)	(217,856)	(349,659)
Cash flows used in financing activities:
Change in uncashed checks	5,404	(3,705)	132
Tax payments related to withholdings on vested restricted stock	(5,331)	(7,429)	(3,266)
Repurchases of common stock	(74,844)	(21,390)	(45,080)
Deferred financing costs paid	(2,171)	(10,079)	(4,027)
Payments on finance leases	(4,469)	(586)	0
Premiums paid on early extinguishment of debt	0	(2,701)	(1,238)
Principal payments on debt	(7,535)	(852,535)	(405,768)
Proceeds from issuance of debt, net of discount	0	845,000	348,250
Borrowings from revolving credit facility	150,000	0	50,000
Payments on revolving credit facility	(150,000)	0	(50,000)
Net cash used in financing activities	(88,946)	(53,425)	(110,997)
Effect of exchange rate change on cash	4,919	3,573	(5,446)
Increase (decrease) in cash and cash equivalents	147,110	145,484	(92,892)
Cash and cash equivalents, beginning of year	371,991	226,507	319,399
Cash and cash equivalents, end of year	519,101	371,991	226,507
Cash payments for interest and income taxes:
Interest paid	72,535	60,852	89,171
Income taxes paid, net of refunds	53,123	27,035	20,036
Non-cash investing activities:
Property, plant and equipment accrued	3,536	30,964	15,657
Payable for estimated purchase price adjustment	$ 0	$ 0	$ 4,032

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Earnings	Accumulated Earnings Cumulative Effect, Period of Adoption, Adjustment
Beginning balance (in shares) at Dec. 31, 2017			56,501
Beginning balance at Dec. 31, 2017	$ 1,188,202	$ (1,564)	$ 565	$ 686,962	$ (172,407)	$ 673,082	$ (1,564)
Increase (Decrease) in Stockholders' Equity
Net income	65,636					65,636
Other comprehensive income (loss)	(50,964)				(50,964)
Stock-based compensation	16,792			16,792
Issuance of common stock for restricted share vesting, net of employee tax withholding (in shares)			160
Issuance of common stock for restricted share vesting, net of employee tax withholdings	$ (3,266)		$ 1	(3,267)
Repurchases of common stock (in shares)	(800)		(814)
Repurchases of common stock	$ (45,080)		$ (8)	(45,072)
Ending balance (in shares) at Dec. 31, 2018			55,847
Ending balance at Dec. 31, 2018	1,169,756		$ 558	655,415	(223,371)	737,154
Increase (Decrease) in Stockholders' Equity
Net income	97,740					97,740
Other comprehensive income (loss)	13,320				13,320
Stock-based compensation	17,816			17,816
Issuance of common stock for restricted share vesting, net of employee tax withholding (in shares)			249
Issuance of common stock for restricted share vesting, net of employee tax withholdings	$ (7,429)		$ 3	(7,432)
Repurchases of common stock (in shares)	(300)		(298)
Repurchases of common stock	$ (21,390)		$ (3)	(21,387)
Ending balance (in shares) at Dec. 31, 2019			55,798
Ending balance at Dec. 31, 2019	1,269,813		$ 558	644,412	(210,051)	834,894
Increase (Decrease) in Stockholders' Equity
Net income	134,837					134,837
Other comprehensive income (loss)	(1,426)				(1,426)
Stock-based compensation	18,502			18,502
Issuance of common stock for restricted share vesting, net of employee tax withholding (in shares)			179
Issuance of common stock for restricted share vesting, net of employee tax withholdings	$ (5,331)		$ 2	(5,333)
Repurchases of common stock (in shares)	(1,200)		(1,204)
Repurchases of common stock	$ (74,844)		$ (12)	(74,832)
Ending balance (in shares) at Dec. 31, 2020			54,773
Ending balance at Dec. 31, 2020	$ 1,341,551		$ 548	$ 582,749	$ (211,477)	$ 969,731

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (PARENTHETICAL) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
Statement of Stockholders' Equity [Abstract]
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01

OPERATIONS	12 Months Ended
OPERATIONS	Dec. 31, 2020
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 and industrial services throughout North America. The Company is also the largest re-refiner and recycler of used oil and the largest provider of parts cleaning and related environmental services to commercial, industrial and automotive customers in North America. A novel strain of coronavirus ("COVID-19") was first identified in December 2019, and subsequently declared a global pandemic by the World Health Organization on March 11, 2020. As a result of the outbreak, many companies experienced significant disruptions in their operations, workforce and markets served, also resulting in a significant reduction in the demand for petroleum-based products. Areas of the Company's businesses and operations were adversely impacted by the effects of COVID-19 when circumstances surrounding and responses to the pandemic, including stay-at-home orders, began to materialize in North America. These disruptions had a significant impact on the Company's operating results for the year ended December 31, 2020. The Company expects that operations will continue to be impacted. The full extent of the ongoing COVID-19 pandemic and the resulting changes in demand for oil and the impact on the Company's operations is uncertain. A prolonged disruption could have a material adverse impact on financial results and business operations of the Company.

SIGNIFICANT ACCOUNTING POLICIES

12 Months Ended

Dec. 31, 2020

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 financial 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.

Reclassifications

Certain prior year amounts have been reclassified to conform to the current year presentation. These reclassifications have no impact on previously reported subtotals.

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. 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. 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 consolidated statements 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. As of December 31, 2020 and 2019, the Company had

total marketable securities and cash equivalents as follows (in thousands):


	December 31, 2020		December 31, 2019
Commercial paper	$	—	$	2,395
Total cash equivalents	—		2,395
U.S. Treasury securities	28,901		12,406
Corporate notes and bonds	22,956		26,678
Commercial paper	—		3,337

Total marketable securities	51,857		42,421
Total	$	51,857	$	44,816

Realized gains and losses on sales of available-for-sale marketable securities in the years presented 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, reasonable expectations of future collections, 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 direct 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 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, net (excluding landfill assets and finance lease right of use assets)

Property, plant and equipment, net is stated at cost less accumulated depreciation. 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. Gains and losses on the sale of property, plant and equipment are included in other (expense) income, net. During the construction and development period of an asset, the costs incurred are classified as construction-in-progress. When the asset is ready for its intended use, the asset is reclassified to an appropriate asset classification and depreciation or amortization commences. The Company depreciates and amortizes the capitalized 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 tests asset groups for impairment whenever events or changes in circumstances indicate that the carrying value may not be recoverable. An impairment in the carrying value of long-lived assets is recognized if the expected future undiscounted cash flows derived from the assets, or group of assets, are less than their carrying value. The Company did not record any impairment charges related to long-lived assets in the periods presented.

Goodwill

Goodwill is comprised of the purchase price of business acquisitions in excess of the fair value of the net assets acquired. Goodwill 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. If the carrying value of a reporting unit exceeds the fair value, an impairment loss will be recognized in an amount equal to that excess, limited to the total amount of goodwill allocated to that reporting unit. The Company did not recognize any impairment losses in any of the periods presented. See Note 7, "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 five to 30 years on a straight-line basis. Finite-lived intangible assets are amortized on a straight-line basis over their respective useful lives, which range from five to 20 years.

All 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.

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 $10.9 million, $12.3 million and $10.3 million for the years ended December 31, 2020, 2019 and 2018, respectively. Changes in the determination of when the landfill will cease accepting waste, either through a business decision by the Company, determination that expansion capacity should no longer be considered probable or changes in estimates on annual airspace consumption, will impact the amortization expense of the landfill assets. 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 highly probable of ultimately being permitted. As of December 31, 2020, there were no unpermitted expansions included in the Company's landfill accounting model. If actual expansion airspace is significantly different from management's estimate of expansion airspace, the amortization rates used for the units-of-consumption method would change, therefore impacting our profitability.

As of December 31, 2020, the Company had 9 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:


Facility Name	Location	Remaining Lives (Years)	Permitted Remaining Highly Probable Airspace (cubic yards) (in thousands)
Buttonwillow	California	22	5,739
Deer Park	Texas	2	67
Deer Trail	Colorado	27	1,629
Grassy Mountain	Utah	41	4,710
Kimball	Nebraska	6	144
Lambton	Ontario, Canada	51	4,633
Lone Mountain	Oklahoma	32	3,803
Ryley	Alberta, Canada	5	575
Sawyer	North Dakota	68	3,416
			24,716

At December 31, 2020 and 2019, 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, 2018 through December 31, 2020 (in thousands of cubic yards):


	2020	2019	2018
Remaining capacity, beginning of year	28,494	29,760	31,113
Changes in highly probable airspace, net	(2,962)	—	(223)
Consumed	(816)	(1,266)	(1,130)
Remaining capacity, end of year	24,716	28,494	29,760

During the year ended December 31, 2020, the Company took actions to begin the closure of two of the Company's commercial landfill sites, Altair and Westmorland, and is therefore classifying these landfills as inactive as of December 31, 2020. During 2020, the Altair landfill, a non-hazardous landfill, reached permitted capacity. Airspace consumed from the Altair landfill in the years ended December 31, 2020, 2019 and 2018 was 25, 132 and 127 thousand cubic yards, respectively. During 2020, the Company decided to close the Westmorland landfill, a hazardous landfill, due to the costs of obtaining and

maintaining permits and operating the landfill. No airspace had been consumed at the Westmorland landfill in the years ended December 31, 2020, 2019 and 2018. The change in the highly probable airspace, net in the table above is predominately the result of the Company's decision to close the Westmorland and Altair landfills.

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 consolidated statements of cash flows.

Landfill final closure and post-closure liabilities—The balance of landfill final closure and post-closure liabilities at December 31, 2020 and 2019 was $48.4 million and $39.4 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. 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 ceases 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 both 2020 and 2019) and discounted at the Company's credit-adjusted risk-free interest rate (5.60% and 6.02% during 2020 and 2019, respectively).

Non-Landfill Closure and Post-Closure Liabilities

The balance of non-landfill closure and post-closure liabilities at December 31, 2020 and 2019 was $39.5 million and $36.3 million, respectively. Non-landfill closure and post-closure obligations arise when the Company commences non-landfill facility operations and 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 typically 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 government agencies; (ii) estimates as to when future operations may cease; (iii) cost estimates of closing the non-landfill facility using the inflation rate to the time of closing; and (iv) discounting the future value back to the present using the credit-adjusted risk-free interest rate.

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 estimate as to when future operations at a location might cease or in the expected timing of the costs. Changes in estimates for non-landfill closure and post-closure events immediately impact the liability and the value of the corresponding asset. If a change is made to a fully-amortized asset, the adjustment is charged immediately to expense. When a change in estimate relates to an asset that has not been fully amortized, the adjustment to the asset is recognized in income prospectively as a component of amortization. Historically, changes to non-landfill closure and post-closure estimates have not been material.

Remedial Liabilities

The balance of remedial liabilities at December 31, 2020 and 2019 was $114.8 million and $114.2 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 18 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 obligations, have been identified as potentially responsible parties ("PRPs") or potential PRPs. The Company's estimate of remedial liabilities involves 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 in the consolidated statements of operations 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 Chemical Services Division of Safety-Kleen ("CSD") assets (or the respective predecessors of the Company or such sellers) transported or disposed of waste, including 130 Superfund sites as of December 31, 2020. The Company periodically reviews and evaluates sites requiring remediation 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 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 liability is recognized.

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 previously identified. 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 Company incurring the 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 when the timing of the payments is determinable and the amounts are estimable. 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. Discount rates used in the present value determination of the Company's remedial liabilities range from 1.37% to 4.90%.

Self-Insurance Liabilities

The Company self-insures a significant portion of expected losses related to workers' compensation, employee medical, comprehensive general liability and vehicle liability. Liabilities associated with these losses are recorded based on the Company's estimates of the ultimate cost to settle incurred claims. These recorded liabilities are estimated based on independent actuarial estimates and judgments which consider the frequency and settlement amount of historical claims data.

Revenue Recognition

The Company generates service 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.

The majority of the Company’s revenues are for services, which are recognized based on time and materials incurred at contractually agreed-upon rates. Product revenues are recognized when the products are delivered and control transfers to the customer. 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. 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 operations, the Company 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 government authorities. The Company excludes sales and other excise taxes that it collects from customers from its revenues.

The Company's Environmental Services operating segment generally has the following three sources of revenue:

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, using time and materials incurred as a basis for measuring the satisfaction of the performance obligation. 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 the relative standalone selling price (i.e. the estimated price that a customer would pay for the services on a standalone basis). Revenues and the related costs from waste that is not yet completely processed and disposed of are deferred. The deferred revenues and costs are recognized when the disposal 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 or other locations. 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. More recently, demand has increased for projects involving contagion disinfection, decontamination and disposal services in response to the COVID-19 pandemic. Field and emergency response 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 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 and Other—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 upstream energy services, such as exploration and drilling for industrial oil and gas customers. 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.

The Company's Safety-Kleen operating segment generally has the following two sources of revenue:

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, vacuum 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 sale of complementary supply products including automotive fluids and shop supplies and other environmental services. Parts washer services include customer use of our parts washer equipment, cleaning and maintenance of the parts washer equipment and removal and replacement of 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.

Safety-Kleen Oil—Revenues from Safety-Kleen Oil 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 and pulp and paper companies. The used oil is also processed into vacuum gas oil which can be further re-refined into lubricant base oils or sold directly into the marine diesel oil fuel market. 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.

Foreign Currency

The Company has international operations, substantially all of which are located in Canada from an operational perspective with more limited administrative support services located in India. The functional currencies of foreign operations are the 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 from transactions not denominated in the functional currency of an entity 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 consolidated statements of operations.

Advertising Expense

Advertising costs are expensed as incurred. Advertising expense was $9.0 million in 2020, $9.8 million in 2019 and $10.5 million in 2018.

Government Grants

On March 27, 2020, the Coronavirus Aid, Relief and Economic Security Act ("CARES Act") was signed into law in response to the widespread economic impact of the COVID-19 pandemic, providing companies, among other things, tax credits for a portion of wages paid to qualifying employees. Additionally, the Canadian government enacted the Canada Emergency Wage Subsidy ("CEWS") to help employers offset a portion of their employee wages.

During the year ended December 31, 2020, the Company recorded a benefit of $42.3 million as an offset to the related operating expenses in either cost of revenues or selling, general and administrative expenses for the eligible employee retention

credit under the CARES Act and the subsidy under CEWS, as amended. The benefits received under these government sponsored programs do not require repayment.

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 established at the grant date. The expense for these awards is recognized over the requisite service period when management believes it is probable those performance targets will be achieved. The fair value of the Company's grants are based on the closing price of the Company's common stock on the respective dates of grant. Forfeitures are recognized as they occur. Stock-based compensation is recognized in selling, general and administrative expense.

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 upon 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. Liabilities for unrecognized tax benefits are included within other long-term liabilities in the consolidated balance sheets.

The Company recognizes interest and penalties related to unrecognized tax benefits within the provision for income taxes line in the consolidated statements of operations. Accrued interest and penalties are included within the 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.

Leases

The Company’s leases predominately relate to real estate, equipment, such as vehicles and industrial equipment utilized in operations, and rail cars utilized in connection with the Company’s transportation needs. Contracts are reviewed at inception to determine if the arrangement is a lease and, if so, whether it is an operating or finance lease. For all of its leases, the Company has elected not to separate lease and nonlease components, such as common area maintenance.

The Company generally enters into long-term real estate leases with three to ten-year terms and long-term non-real estate leases with two to eight-year terms. In the normal course of business, the Company also enters into short-term leases having terms of less than one-year. These leases are generally equipment leases entered into for short periods of time (e.g. daily, weekly or monthly) to satisfy immediate and/or short-term operational needs of the business which can arise based upon the nature of particular services performed or seasonality factors. The Company has elected not to recognize right of use ("ROU") assets and lease liabilities for these short-term leases. Expense for all such short-term leases is disclosed as short-term lease cost as shown in Note 18, "Leases."

Operating and finance leases with terms exceeding one year are recognized as ROU assets and lease liabilities and measured based on the present value of the future lease payments over the lease term at commencement date. When applicable, the ROU asset includes any lease payments made at or before the commencement date and initial direct costs incurred and is reduced by lease incentives received under the lease agreement.

Certain of the Company's real estate leases contain escalating future lease payments. Escalating lease payments that are based upon explicit amounts contained in the lease or an index (e.g., consumer price index) are included in its determination of future lease payments to determine the ROU asset and lease liability recognized at the commencement date. Any differences in the future lease payments from initial recognition are not anticipated to be material and will be recorded as variable lease cost in the period incurred. The variable lease cost will also include the Company’s portion of property tax, utilities and common area maintenance. A significant portion of the Company’s real estate lease agreements include renewal periods at the Company’s option. The Company includes these renewal periods in the lease term only when renewal is reasonably certain based upon facts and circumstances specific to the lease and known by the Company. Certain of the equipment and rail car leases transfer ownership upon the conclusion of the lease term and as such, are classified as finance leases. Leases containing purchase options are classified as finance leases only when it is reasonably certain that the Company will execute such options.

The Company uses its incremental borrowing rate on collateralized debt based on the information available at the lease commencement date in determining the present value of future lease payments as the implicit rate is typically not readily determinable.

For operating leases, lease cost is recognized on a straight-line basis over the lease term and is included in cost of revenues or selling, general and administrative expenses depending on the use of the asset. For finance leases, ROU assets are amortized on a straight-line basis over the shorter of the lease term or the estimated useful life of the leased asset and interest expense is recognized based on the incremental borrowing rate. Amortization and interest expense for finance leases are included in depreciation and amortization and interest expense, net of interest income, respectively.

The Company adopted Accounting Standards Codification 842, Leases ("ASC 842"), on January 1, 2019 using the modified retrospective method of adoption. Prior period amounts have not been adjusted and continue to be reported in accordance with the Company's historical accounting methodology pursuant to Accounting Standards Codification 840, Leases. The standard did not have a material impact on the consolidated statements of operations or cash flows.

REVENUES

12 Months Ended

Dec. 31, 2020

Revenue from Contract with Customer [Abstract]

REVENUES

Disaggregation of Revenue

We disaggregate the Company’s third-party revenues by geographic location and source of revenue as we believe these categories depict how revenue and cash flows are affected by economic factors (in thousands):


	For the year ended December 31, 2020
	Environmental Services		Safety-Kleen		Corporate		Total
Primary Geographical Markets
United States	$	1,690,256	$	1,049,975	$	(674)	$	2,739,557
Canada	313,825		89,751		964		404,540
Total third-party revenues	$	2,004,081	$	1,139,726	$	290	$	3,144,097

Sources of Revenue (1)
Technical Services	$	1,062,714	$	—	$	—	$	1,062,714
Field and Emergency Response Services	461,036		—		—		461,036
Industrial Services and Other	480,331		—		290		480,621
Safety-Kleen Environmental Services	—		809,236		—		809,236
Safety-Kleen Oil	—		330,490		—		330,490
Total third-party revenues	$	2,004,081	$	1,139,726	$	290	$	3,144,097


	For the year ended December 31, 2019
	Environmental Services		Safety-Kleen		Corporate		Total
Primary Geographical Markets
United States	$	1,721,322	$	1,220,096	$	(586)	$	2,940,832
Canada	371,041		98,595		1,722		471,358
Total third-party revenues	$	2,092,363	$	1,318,691	$	1,136	$	3,412,190

Sources of Revenue (1)
Technical Services	$	1,120,043	$	—	$	—	$	1,120,043
Field and Emergency Response Services	340,906		—		—		340,906
Industrial Services and Other (2)	631,414		—		1,136		632,550
Safety-Kleen Environmental Services	—		851,520		—		851,520
Safety-Kleen Oil	—		467,171		—		467,171
Total third-party revenues	$	2,092,363	$	1,318,691	$	1,136	$	3,412,190


	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 and Other (3)	661,728		—		1,105		662,833
Safety-Kleen Environmental Services	—		795,077		—		795,077
Safety-Kleen Oil	—		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 Safety-Kleen Oil 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. Safety-Kleen Oil and Safety-Kleen Environmental Services product sales are recognized at a point in time.

(2)Environmental Services third-party revenues of $117.0 million and Corporate third party revenues of $1.1 million previously reported as Oil, Gas and Lodging Services and Other for the year ended December 31, 2019 are now reported within Industrial Services and Other based on relative materiality to the business.

(3)Environmental Services third-party revenues of $119.8 million and Corporate third party revenues of $1.1 million previously reported as Oil, Gas and Lodging Services and Other for the year ended December 31, 2018 are now reported within Industrial Services and Other based on relative materiality to the business.

Contract Balances


(in thousands)	December 31, 2020		December 31, 2019
Receivables	$	611,534	$	644,738
Contract assets (unbilled receivables)	55,681		56,326
Contract liabilities (deferred revenue)	74,066		73,370

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 reported on the consolidated balance sheet on a contract-by-contract basis at the end of each reporting period. 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 management's 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. 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.

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. As of December 31, 2020 and 2019, the Company's deferred contract costs totaled $22.8 million and $21.7 million, respectively. Deferred parts washer costs are recognized over the service interval as the customer receives the benefit of the services, and deferred costs related to treatment and disposal of waste are recognized when the corresponding waste is disposed. Deferred costs are included 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.

- Definition

The entire disclosure of revenue from contract with customer to transfer good or service and to transfer nonfinancial asset. Includes, but is not limited to, disaggregation of revenue, credit loss recognized from contract with customer, judgment and change in judgment related to contract with customer, and asset recognized from cost incurred to obtain or fulfill contract with customer. Excludes insurance and lease contracts.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-URI http://asc.fasb.org/topic&trid=49130388

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130551-203045

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (b)(2)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130556-203045

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 12
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130554-203045

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130550-203045

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 12
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130554-203045

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 12
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130554-203045

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 12
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130554-203045

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130558-203045

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 12
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130554-203045

+ Details

BUSINESS COMBINATIONS	12 Months Ended
BUSINESS COMBINATIONS	Dec. 31, 2020
Business Combinations [Abstract]
BUSINESS COMBINATIONS	BUSINESS COMBINATIONS 2020 Acquisition On April 17, 2020, the Company acquired a privately-owned business for $8.8 million cash consideration. The acquired company expands the Safety-Kleen segment's oil re-refining operations to the northeast United States. In connection with this acquisition, a preliminary goodwill amount of $1.4 million was recognized. The results of operations of this acquired business were not material in 2020. 2019 Acquisitions On May 31, 2019, the Company acquired a privately-owned business for $14.8 million cash consideration. The acquired company expands the environmental services and hazardous materials management services of the Company and is included in the Environmental Services segment. In connection with this acquisition, a goodwill amount of $7.4 million was recognized. On March 1, 2019, the Company acquired certain assets of a privately-owned business for $10.4 million cash consideration. The acquired business complements the Safety-Kleen segment's core service offerings, such as used motor oil collection, parts washers, oil filter recycling and vacuum services. In connection with this acquisition, a goodwill amount of $5.2 million was recognized. The results of operations of these acquired businesses were not material in 2019. Pro forma revenue and earnings amounts on a combined basis as if these acquisitions had been completed on January 1, 2018 are immaterial to the consolidated financial statements of the Company since that date. 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 $26.7 million purchase price, net of cash. 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 purchase price of $124.5 million. The Veolia Business has been integrated into the Environmental Services segment. 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 are included in selling, general and administrative expenses in the consolidated statements of operations.

INVENTORIES AND SUPPLIES

12 Months Ended

Dec. 31, 2020

Inventory Disclosure [Abstract]

INVENTORIES AND SUPPLIES

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


	December 31, 2020		December 31, 2019
Oil and oil related products	$	76,209	$	75,408
Supplies and drums	120,007		115,128
Solvent and solutions	8,812		9,973
Other	15,470		14,235
Total inventories and supplies	$	220,498	$	214,744

Supplies and drums inventories consist primarily of drums and containers used in providing the Company's products and services, critical spare parts to support the Company's incinerator and re-refinery operations, and personal protective equipment. Other inventories consist primarily of parts washer components, cleaning fluids, absorbents and automotive fluids, such as windshield washer fluid and antifreeze.

PROPERTY, PLANT, AND EQUIPMENT

12 Months Ended

Dec. 31, 2020

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, 2020		December 31, 2019
Land	$	139,776	$	131,023
Asset retirement costs (non-landfill)	16,407		15,924
Landfill assets	191,687		182,276
Buildings and improvements (1)	509,804		499,159
Camp equipment	159,021		158,277
Vehicles (2)	844,026		785,056
Equipment (3)	1,807,235		1,779,366
Furniture and fixtures	7,082		6,054
Construction in progress	24,378		36,679
	3,699,416		3,593,814
Less - accumulated depreciation and amortization	2,174,118		2,005,663
Total property, plant and equipment, net	$	1,525,298	$	1,588,151

___________________________________

(1) Balances inclusive of gross ROU assets classified as finance leases of $8.9 million and $31.0 million, respectively.

(2) Balances inclusive of gross ROU assets classified as finance leases of $47.2 million and $2.4 million, respectively.

(3) December 31, 2020 balance inclusive of gross ROU assets classified as finance leases of $9.3 million.

Depreciation expense, inclusive of landfill and finance lease amortization was $257.1 million, $265.5 million and $264.3 million for the years ended December 31, 2020, 2019 and 2018, respectively.

GOODWILL AND OTHER INTANGIBLE ASSETS

12 Months Ended

Dec. 31, 2020

Goodwill and Intangible Assets Disclosure [Abstract]

GOODWILL AND OTHER INTANGIBLE ASSETS

The changes in goodwill for the years ended December 31, 2020 and 2019 were as follows (in thousands):


	Environmental Services		Safety-Kleen		Totals
Balance at January 1, 2019	$	207,019	$	307,170	$	514,189
Increase from current period acquisitions	7,378		5,225		12,603
Measurement period adjustments from prior period acquisitions	(2,675)		(1,355)		(4,030)


Foreign currency translation	809		1,442		2,251
Balance at December 31, 2019	$	212,531	$	312,482	$	525,013
Increase from current period acquisition	—		1,439		1,439
Measurement period adjustments from prior period acquisitions	23		—		23
Decrease from disposition of businesses	(674)		—		(674)

Foreign currency translation	506		716		1,222
Balance at December 31, 2020	$	212,386	$	314,637	$	527,023

The Company regularly assesses goodwill for impairment when it is more likely than not that events or changes in the business environment ("triggering events") would reduce the fair value of a reporting unit below its carrying value. The Company considered the effects of COVID-19 and evolving changes in demand and pricing for oil during 2020 but concluded that there were no triggering events requiring an impairment assessment.

Goodwill impairment is also tested annually. The Company conducted its annual impairment test of goodwill as of December 31, 2020 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 the respective carrying values.

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 impairment tests are reasonable, but variations in any of the assumptions may result in different measurements of fair values.

The impacts of any adverse business and market conditions which may 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, or if the impact of the COVID-19 pandemic and macroeconomic factors on the Company and its customers result in significant prolonged changes in demand for our products and services, 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.

As of December 31, 2020 and 2019, the Company's finite-lived and indefinite-lived intangible assets consisted of the following (in thousands):


	December 31, 2020						December 31, 2019
	Cost		Accumulated Amortization		Net			Cost		Accumulated Amortization		Net
Permits	$	183,766	$	95,033	$	88,733		$	184,235	$	87,228	$	97,007
Customer and supplier relationships	382,083		211,895		170,188			401,696		207,884		193,812
Other intangible assets	39,287		34,744		4,543			38,331		33,018		5,313
Total amortizable permits and other intangible assets	605,136		341,672		263,464			624,262		328,130		296,132
Trademarks and trade names	123,156		—		123,156			122,934		—		122,934
Total permits and other intangible assets	$	728,292	$	341,672	$	386,620		$	747,196	$	328,130	$	419,066

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 periods presented, 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, including prolonged macroeconomic impacts from the COVID-19 pandemic as noted above, future impairments may become evident.

Amortization expense of permits and other intangible assets for the years ended December 31, 2020, 2019 and 2018 were $35.8 million, $35.2 million and $34.4 million, respectively.

The expected amortization of the net carrying amount of finite-lived intangible assets at December 31, 2020 is as follows (in thousands):


Years ending December 31,	Expected Amortization
2021	$	30,163
2022	29,911
2023	25,587
2024	24,092
2025	23,121
Thereafter	130,590
	$	263,464

ACCRUED EXPENSES

12 Months Ended

Dec. 31, 2020

Payables and Accruals [Abstract]

ACCRUED EXPENSES

Accrued expenses consisted of the following (in thousands):


	December 31, 2020		December 31, 2019
Accrued insurance	$	77,514	$	74,376
Accrued interest	19,697		21,222
Accrued compensation and benefits	81,437		72,473
Accrued income, real estate, sales and other taxes	25,843		35,749
Interest rate swap liability	33,630		20,840
Accrued other	57,702		51,880
	$	295,823	$	276,540

As of December 31, 2020 and 2019, accrued insurance included employee medical insurance costs of $9.4 million and $14.3 million, respectively, and accruals for losses under our workers' compensation, comprehensive general liability and vehicle liability self-insurance programs of $65.6 million and $59.4 million, respectively.

Accrued compensation and benefits increased from the comparable period in 2019 primarily due to an increase in payroll tax payable of $17.0 million due to the deferral of employer payroll tax payments under the CARES Act which are due to be repaid in the fourth quarter of 2021. This increase was partially offset by decreases in accrued payroll of $4.8 million and accrued bonuses of $3.5 million.

The increase in the fair value of the interest rate swap liability from December 31, 2019 is mainly due to changes in variable interest rates. For additional information relating to the derivative liability, see Note 11, "Financing Arrangements."

CLOSURE AND POST-CLOSURE LIABILITIES

12 Months Ended

Dec. 31, 2020

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, 2019 through December 31, 2020 were as follows (in thousands):


	Landfill Retirement Liability		Non-Landfill Retirement Liability		Total
Balance at January 1, 2019	$	37,809	$	32,122	$	69,931
Liabilities assumed in acquisitions	—		220		220

New asset retirement obligations	2,705		—		2,705

Accretion	2,772		2,829		5,601
Changes in estimates recorded to consolidated statement of operations	248		2,437		2,685
Changes in estimates recorded to consolidated balance sheet	3,303		562		3,865
Expenditures	(7,718)		(2,121)		(9,839)
Currency translation and other	282		201		483
Balance at December 31, 2019	39,401		36,250		75,651
Liabilities assumed in acquisitions	—		265		265

New asset retirement obligations	2,101		—		2,101

Accretion	3,254		3,399		6,653
Changes in estimates recorded to consolidated statement of operations	6,465		103		6,568
Changes in estimates recorded to consolidated balance sheet	481		201		682
Expenditures	(3,445)		(753)		(4,198)
Currency translation and other	155		49		204
Balance at December 31, 2020	$	48,412	$	39,514	$	87,926

During 2020, the Company took actions to begin the closure of two of its commercial landfill sites. The Altair landfill was closed because it had reached permitted capacity. The Westmorland landfill was closed due to the costs of obtaining and maintaining permits and operating the landfill. The 2020 environmental changes in estimates recorded to the consolidated statement of operations included $6.8 million related to the closure of these two commercial landfills. The 2019 environmental changes in estimates recorded to the consolidated statements of operations included $2.3 million related to increased facility closure costs at one of our locations.

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,
2021	$	14,941
2022	7,816
2023	16,181
2024	6,868
2025	5,628
Thereafter	269,477
Undiscounted closure and post-closure liabilities	320,911
Less: Discount at credit-adjusted risk-free rate	(159,164)
Less: Undiscounted estimated closure and post-closure liabilities relating to airspace not yet consumed	(73,821)
Present value of closure and post-closure liabilities	$	87,926

REMEDIAL LIABILITIES

12 Months Ended

Dec. 31, 2020

Environmental Remediation Obligations [Abstract]

REMEDIAL LIABILITIES

The changes to remedial liabilities from January 1, 2019 through December 31, 2020 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, 2019	$	1,838	$	65,315	$	53,864	$	121,017


Accretion	88		2,639		1,808		4,535
Changes in estimates recorded to consolidated statement of operations	(17)		(913)		(2,087)		(3,017)
Expenditures	(59)		(5,079)		(3,724)		(8,862)
Currency translation and other	1		29		470		500
Balance at December 31, 2019	1,851		61,991		50,331		114,173


Accretion	90		2,607		1,701		4,398
Changes in estimates recorded to consolidated statement of operations	(15)		2,873		1,272		4,130
Expenditures	(61)		(4,332)		(3,810)		(8,203)
Currency translation and other	—		(79)		394		315
Balance at December 31, 2020	$	1,865	$	63,060	$	49,888	$	114,813

During 2020, the Company increased its remedial liabilities for an inactive site and a Superfund site by $3.3 million and $1.8 million, respectively, due to updated regulatory remediation requirements received during the year. In 2019, the net reduction in the Company's remedial liabilities from changes in estimates recorded to the consolidated statement of operations was $3.0 million and primarily related to reductions in estimates for remedial activities at five locations.

Anticipated payments at December 31, 2020 (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,
2021	$	12,718
2022	19,275
2023	11,420
2024	9,073
2025	6,526
Thereafter	75,915
Undiscounted remedial liabilities	134,927
Less: Discount	(20,114)
Total remedial liabilities	$	114,813

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, 2020.

Estimates based on type of facility or site (in thousands, except percentages):


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 (37 facilities)	$	42,151	36.7	%	$	10,565
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 (27 facilities)	63,060		54.9		10,716
Superfund sites (16 sites)	9,602		8.4		960
Total	$	114,813	100.0	%	$	22,241

___________________________________

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

Estimates based on amount of potential liability (in thousands, except percentages):


Location	Type of Facility or Site	Remedial Liability(1)		% of Total		Reasonably Possible Additional Liabilities(2)
Baton Rouge, LA	Closed incinerator and landfill	$	25,650	22.3	%	$	4,208
Bridgeport, NJ	Closed incinerator	17,832		15.5		2,510
Mercier, Quebec	Idled incinerator and legal proceedings	11,158		9.7		1,157
Linden, NJ	Operating solvent recycling center	7,220		6.3		758
Various	All other incinerators, landfills, wastewater treatment facilities and service centers (60 facilities)	43,351		37.8		12,648
Various	Superfund sites (each representing less than 5% of total liabilities) (16 sites)	9,602		8.4		960
Total		$	114,813	100.0	%	$	22,241

_________________________________

(1)$24.0 million of the $114.8 million remedial liabilities include estimates related to the legal and administrative proceedings discussed in Note 17, "Commitments and Contingencies," as well as other such estimated remedial liabilities.

(2)Amounts represent the high end of the range of management's best estimate of the reasonably possible additional 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 future changes in available technology, 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. Since the Company's satisfaction of the liabilities will occur over many years, the Company cannot reasonably predict the nature or extent of possible future events or the impact that those events, if any, might have on the current estimates of remedial liabilities.

FINANCING ARRANGEMENTS

12 Months Ended

Dec. 31, 2020

Debt Disclosure [Abstract]

FINANCING ARRANGEMENTS

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


Current Debt:	December 31, 2020		December 31, 2019
Secured senior term loans ("Term Loans")	$	7,535	$	7,535


Long-Term Debt:
Secured senior Term Loans due June 30, 2024	$	719,626	$	727,162
Unsecured senior notes, at 4.875%, due July 15, 2027 ("2027 Notes")	545,000		545,000
Unsecured senior notes, at 5.125%, due July 15, 2029 ("2029 Notes")	300,000		300,000

Long-term debt, at par	1,564,626		1,572,162
Unamortized debt issuance costs and premium, net	(14,985)		(18,046)
Long-term debt, at carrying value	$	1,549,641	$	1,554,116

Financing Activities

Unsecured Senior Notes. On July 2, 2019, the Company completed a private placement of $545.0 million aggregate principal amount of 2027 Notes and $300.0 million aggregate principal amount of 2029 Notes (collectively, the "Notes"). The 2027 Notes will mature on July 15, 2027, and the 2029 Notes will mature on July 15, 2029. Interest payments on each series of the Notes are paid semiannually on January 15 and July 15.

The Company may redeem all or any portion of the 2027 Notes prior to July 15, 2022 or the 2029 Notes prior to July 15, 2024 at a redemption price equal to 100% of the principal amount redeemed plus a make whole premium as of the date of redemption including accrued and unpaid interest, if any, up to the date of redemption. Additionally, prior to July 15, 2022 for

the 2027 Notes and July 15, 2024 for the 2029 Notes, the Company may use cash proceeds of one or more equity offerings to redeem up to 35% in aggregate principal of the 2027 Notes or the 2029 Notes at a redemption price equal to 104.875% or 105.125%, respectively, plus accrued and unpaid interest thereon, if any, up to the date of redemption.

After the dates in the preceding paragraph, the Company may redeem all or any portion of the Notes which remain outstanding at any time upon proper notice at the following redemption prices if redeemed during the twelve-month period commencing on July 15 of the years set forth below plus accrued and unpaid interest, if any, up to the date of redemption:

2027 Notes


Year	Percentage
2022	102.438	%
2023	101.219	%
2024 and thereafter	100.000	%

2029 Notes


Year	Percentage
2024	102.563	%
2025	101.281	%
2026 and thereafter	100.000	%

Concurrently with the closing of the Notes in July 2019, the Company repurchased an aggregate principal amount of $845.0 million of previously outstanding notes due in 2021 ("2021 Notes") using a combination of the net proceeds from the sale of the Notes and available cash. The total amount paid in repurchasing the 2021 Notes was $850.2 million, including $4.0 million of accrued interest. In connection with this repurchase of the 2021 Notes, the Company recorded a loss on early extinguishment of debt of $6.1 million during the year ended December 31, 2019.

The Notes and the related indenture contain various customary non-financial covenants and are guaranteed by substantially all of the Company’s current and future domestic subsidiaries. The Notes are effectively subordinated to the loan agreement under which the Company's Term Loans are outstanding, revolving credit facility and finance lease obligations to the extent of the value of the assets securing such secured indebtedness. The Notes are also effectively subordinated to all indebtedness and other liabilities of the Company's subsidiaries that are not guarantors of the Notes.

Senior Secured Term Loans. 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 Loans. The Incremental Facility Amendment increased the principal amount of the Term Loans outstanding by $350.0 million. The total Term Loans outstanding 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 Loans 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 applicable interest rate margins for the Term Loans are 1.75% for Eurocurrency borrowings and 0.75% for base rate borrowings. The effective annual interest rate of the Term Loans on December 31, 2020 was 1.90%.

Concurrently with the closing on July 19, 2018 of the Incremental Facility Amendment, the Company repurchased $322.0 million aggregate principal of previously outstanding unsecured senior notes. The total amount paid to repurchase those 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 principal of those previously outstanding notes. In connection with this redemption, the Company recorded a loss on early extinguishment of debt of $2.5 million during the year ended December 31, 2018.

As of December 31, 2020 and December 31, 2019, the estimated fair value of the Company’s outstanding long-term debt, including the current portion, was $1.6 billion. The Company’s estimates of the fair value of its long-term debt, including the current portion, are based on quoted market prices or other available market data which are considered Level 2 measures according to the fair value hierarchy. Level 2 utilizes quoted market prices in markets that are not active, broker or dealer quotation, or alternative pricing sources with reasonable levels of price transparency for similar assets and liabilities.

Revolving Credit Facility. On October 28, 2020, 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 $350.0 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 $50.0 million. Availability under the U.S. line is subject to a borrowing base primarily 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 primarily 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 revolving credit facility will expire on October 28, 2025.

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 1.50% to 1.75% 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 0.50% to 0.75% 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 0.375% per annum of the unused commitment. For outstanding letters of credit, the Company pays 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. In the event that LIBOR ceases to be available during the term of the revolving credit facility, the amended and restated credit agreement provides procedures to determine a LIBOR successor rate.

The Company utilizes letters of credit issued under the revolving credit facility primarily as security for our insurance program that includes casualty and financial assurance.

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.

On March 31, 2020, the Company borrowed $150.0 million under the revolving credit facility. The Company repaid the full amount of the borrowing during 2020. The revolving credit facility had no outstanding loan balances at December 31, 2020 and 2019 and had availability of $264.0 million and outstanding letters of credit of $120.6 million at December 31, 2020.

Cash Flow Hedges

The Company’s strategy to hedge against fluctuations in variable interest rates involves entering into interest rate derivative agreements.

Although the interest rate on the Term Loans is variable, the Company has effectively fixed the interest rate on $350.0 million principal 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 one-month LIBOR index and pays interest at a weighted average rate of approximately 2.92%, resulting in an effective annual interest rate of approximately 4.67%.

The Company recognizes derivative instruments as either assets or liabilities on the consolidated balance sheet at fair value. No ineffectiveness has been identified on these swaps and, therefore the change in fair value is recorded in stockholders’ equity as a component of accumulated other comprehensive loss. Amounts are reclassified from accumulated other comprehensive loss into interest expense on the consolidated statement of operations in the same period or periods during which the hedged transactions affect earnings.

As of December 31, 2020 and December 31, 2019, the Company recorded a derivative liability with a fair value of $33.6 million and $20.8 million, respectively, within accrued expenses in connection with these cash flow hedges.

The fair value of the interest rate swaps 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 interest rate swaps and as such is considered a Level 2 measure according to the fair value hierarchy.

INCOME TAXES

12 Months Ended

Dec. 31, 2020

Income Tax Disclosure [Abstract]

INCOME TAXES

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


	For the years ended December 31,
	2020		2019		2018
Domestic	$	168,117	$	156,571	$	115,070
Foreign	6,433		(8,332)		(20,588)
Total	$	174,550	$	148,239	$	94,482

The provision for income taxes consisted of the following (in thousands, except percentages):


	For the years ended December 31,
	2020		2019		2018
Current:
Federal	$	33,327	$	20,482	$	(7,677)
State	14,575		14,564		12,653
Foreign	1,559		7,448		4,781
	49,461		42,494		9,757
Deferred
Federal	(965)		7,933		19,899
State	(2,506)		550		(1,205)
Foreign	(6,277)		(478)		395
	(9,748)		8,005		19,089
Provision for income taxes	$	39,713	$	50,499	$	28,846

Effective tax rate	22.8%		34.1%		30.5%

The Company's effective income tax rate varied from the amount computed using the statutory federal income tax rate of 21% as follows (in thousands):


	For the years ended December 31,
	2020		2019		2018
Tax expense at US statutory rate	$	36,655	$	31,130	$	19,841
State income taxes, net of federal benefit	9,837		10,597		8,711
Foreign rate differential	1,256		276		(1,124)
Valuation allowance	(11,339)		4,459		10,466


Uncertain tax position interest and penalties	(712)		474		(1,806)
Tax credits	2,039		(50)		(9,799)
Non-deductible compensation	1,406		1,922		1,813
Other	571		1,691		1,032
Adjustment for Tax Cuts and Jobs Act	—		—		(288)
Provision for income taxes	$	39,713	$	50,499	$	28,846

The valuation allowance benefit of $11.3 million recognized in 2020 is predominately related to taxable earnings in certain Canadian entities that benefited from the wage subsidy received under the CEWS. In addition, the foreign tax credit that expired in 2020 had a full valuation allowance which was also written off, contributing to the valuation allowance benefit in the table above. The foreign tax credit expiration and valuation allowance write off had no net impact to the provision for income taxes.

During 2018, the Company 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 (shown as Tax credits in the table above). The Company collected the refund during 2020.

During the years ended December 31, 2020 and December 31, 2018, the Company recorded $1.3 million and $5.0 million, respective, 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 for income taxes. See Note 15, "Accumulated Other Comprehensive Loss," for additional information related to these transactions.

The components of the total net deferred tax assets and liabilities as of December 31, 2020 and 2019 were as follows (in thousands):


	2020		2019
Deferred tax assets:

Provision for doubtful accounts	$	10,305	$	8,949
Closure, post-closure and remedial liabilities	28,665		26,960
Operating lease liabilities	38,151		40,879
Accrued expenses	16,797		17,602
Accrued compensation and benefits	11,372		7,155
Net operating loss carryforwards(1)	50,433		50,824
Tax credit carryforwards(2)	14,471		16,909
Interest rate swap liability	10,089		6,252
Stock-based compensation	3,040		2,435
Other	5,553		8,342
Total deferred tax assets	188,876		186,307
Deferred tax liabilities:
Property, plant and equipment	(194,604)		(184,594)
Operating lease right-of-use assets	(38,018)		(40,985)
Permits and other intangible assets	(95,492)		(98,654)
Prepaid expenses	(9,660)		(9,694)
Total deferred tax liabilities	(337,774)		(333,927)
Total net deferred tax liability before valuation allowance	(148,898)		(147,620)
Less valuation allowance	(77,044)		(83,643)
Net deferred tax liabilities	$	(225,942)	$	(231,263)

___________________________________

(1)As of December 31, 2020, the net operating loss carryforwards included (i) state net operating loss carryovers of $193.2 million which will begin to expire in 2021, (ii) federal net operating loss carryforwards of $16.8 million which will begin to expire in 2025 and (iii) foreign net operating loss carryforwards of $151.5 million which will begin to expire in 2021.

(2)As of December 31, 2020, the foreign tax credit carryforwards of $14.1 million will expire between 2021 and 2024.

The Company has not accrued for any remaining undistributed 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. The components of the total valuation allowance as of December 31, 2020 and 2019 were as follows (in thousands):


	2020		2019
Allowance related to:
Foreign tax credits	14,127		16,565
Acquired federal net operating losses	779		779
State net operating loss carryforwards	10,429		10,663
Foreign net operating loss carryforwards	29,839		34,149
Deferred tax assets of a Canadian subsidiary	11,468		14,922
Realized and unrealized capital losses	10,402		6,565
Total valuation allowance	$	77,044	$	83,643

The changes to unrecognized tax benefits (excluding related penalties and interest) from January 1, 2018 through December 31, 2020, were as follows (in thousands):


	2020		2019		2018
Unrecognized tax benefits, beginning of year	$	6,414	$	3,159	$	5,121

(Reductions) additions to prior year tax positions	(833)		3,354		(625)

Expirations	(203)		(209)		(1,115)

Foreign currency translation	112		110		(222)
Unrecognized tax benefits, end of year	$	5,490	$	6,414	$	3,159

The unrecognized tax benefits at December 31, 2020 if and when recognized will affect the annual effective tax rate. However, the balance at December 31, 2020 included $3.1 million of unrecognized tax benefits for Canadian Revenue Agency transfer pricing adjustments. Should these be recognized, the Company would request relief from double taxation. Therefore, an offsetting benefit of $3.1 million would also recognized resulting in no net effect on the annual effective tax rate.

The Company does not currently believe that the total unrecognized tax benefits will change within the next 12 months.

At December 31, 2020, 2019 and 2018, the Company had accrued interest of $2.1 million, $1.7 million and $0.8 million, respectively, relative to unrecognized tax benefits. Interest expense and penalties relative to unrecognized tax benefits for the years ended December 31, 2020, 2019 and 2018 were immaterial.

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 IRS for calendar years 2015 through 2019. The Company may be subject to examination by Canadian federal and provincial authorities for calendar years 2013 through 2019 and by state and local revenue authorities for calendar years 2014 through 2019. 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.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References + Details

EARNINGS PER SHARE

12 Months Ended

Dec. 31, 2020

Earnings Per Share [Abstract]

EARNINGS PER SHARE

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


	For the years ended December 31,
	2020		2019		2018
Numerator for basic and diluted earnings per share:
Net income	$	134,837	$	97,740	$	65,636
Denominator:
Weighted basic shares outstanding	55,479		55,845		56,148
Dilutive effect of equity-based compensation awards	211		284		192
Weighted dilutive shares outstanding	55,690		56,129		56,340

Basic earnings per share	$	2.43	$	1.75	$	1.17
Diluted earnings per share	$	2.42	$	1.74	$	1.16

For the years ended December 31, 2020, 2019 and 2018, all then outstanding performance awards and restricted stock awards were included in the calculation of diluted earnings per share except for 53,667, 122,785 and 79,390 respectively, of performance stock awards for which the performance criteria were not attained at the reporting dates and 8,878, 16,304 and 121,803 respectively, of restricted stock awards and performance stock awards which were excluded as their inclusion would have had an antidilutive effect.

STOCKHOLDERS' EQUITY	12 Months Ended
STOCKHOLDERS' EQUITY	Dec. 31, 2020
Equity [Abstract]
STOCKHOLDERS' EQUITY	STOCKHOLDERS' EQUITY The Company's board of directors has authorized the repurchase of up to $600.0 million of the Company's common stock. 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, 2020, 2019 and 2018, the Company repurchased and retired a total of 1.2 million, 0.3 million and 0.8 million shares, respectively, of the Company's common stock for total costs of $74.8 million, $21.4 million and $45.1 million, respectively. As of December 31, 2020, an additional $209.9 million remained available for repurchase of shares under this program.

ACCUMULATED OTHER COMPREHENSIVE LOSS

12 Months Ended

Dec. 31, 2020

Equity [Abstract]

ACCUMULATED OTHER COMPREHENSIVE LOSS

The changes in accumulated other comprehensive loss by component and related tax impacts for the years ended December 31, 2020, 2019 and 2018 were as follows (in thousands):


	Foreign Currency Translation Adjustments		Unrealized (Losses) Gains on Available-for-Sale Securities		Unrealized Loss on Interest Rate Hedge		Unrealized (loss) gain on unfunded pension liability		Total
Balance at January 1, 2018	$	(170,575)	$	(146)	$	—	$	(1,686)	$	(172,407)
Other comprehensive (loss) income before reclassifications	(47,374)		182		(9,579)		124		(56,647)
Amounts reclassified out of accumulated other comprehensive loss	—		—		806		—		806
Tax benefit (expense)	5,024		(105)		—		(42)		4,877
Other comprehensive (loss) income, net of tax	(42,350)		77		(8,773)		82		(50,964)
Balance at December 31, 2018	(212,925)		(69)		(8,773)		(1,604)		(223,371)
Other comprehensive income (loss) before reclassifications	25,130		(70)		(14,401)		60		10,719
Amounts reclassified out of accumulated other comprehensive loss	—		332		2,335		—		2,667
Tax expense	—		(50)		—		(16)		(66)
Other comprehensive income (loss)	25,130		212		(12,066)		44		13,320
Balance at December 31, 2019	(187,795)		143		(20,839)		(1,560)		(210,051)
Other comprehensive income (loss) before reclassifications	10,212		(10)		(20,970)		(255)		(11,023)
Amounts reclassified out of accumulated other comprehensive loss	—		—		8,180		—		8,180
Tax benefit	1,349		2		—		66		1,417
Other comprehensive income (loss)	11,561		(8)		(12,790)		(189)		(1,426)
Balance at December 31, 2020	$	(176,234)	$	135	$	(33,629)	$	(1,749)	$	(211,477)

During the years ended December 31, 2020 and December 31, 2018, the Company converted intercompany loans with a foreign subsidiary to equity, which resulted in deductible tax losses. The loans had been historically treated as a component of the Company’s investment 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 tax benefits of $1.3 million and $5.0 million, respectively, which were triggered by the conversions were therefore allocated to other comprehensive loss rather than net income.

The amounts reclassified out of accumulated other comprehensive loss into the consolidated statement of operations, with presentation location, during the years ended December 31, 2020, 2019 and 2018 were as follows (in thousands):


	For the years ended December 31,
Other Comprehensive Income Components	2020		2019		2018		Location
Unrealized loss on available-for-sale securities	$	—	$	(332)	$	—	Other (expense) income, net
Unrealized loss on interest rate hedge	(8,180)		(2,335)		(806)		Interest expense, net of interest income

STOCK-BASED COMPENSATION

12 Months Ended

Dec. 31, 2020

Share-based Payment Arrangement [Abstract]

STOCK-BASED COMPENSATION

Stock-Based Compensation

On June 3, 2020, our shareholders approved the Clean Harbors, Inc. 2020 Stock Incentive Plan (the "2020 Plan"). The 2020 Plan provides for future awards of up to 2.5 million shares of the Company’s common stock (subject to certain anti-dilution adjustments) in the form of stock options, stock appreciation rights, restricted stock, restricted stock units and other stock-based awards. The 2020 Plan is administered by the Compensation Committee of the Company’s Board of Directors. The Company's previous stock incentive plan (the "2010 Plan") expired on May 10, 2020. In connection with the adoption of the 2020 Plan, no further awards will be made under the 2010 Plan.

The Company grants 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 conditions 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 subsequent to the attainment of any performance conditions.

Total stock-based compensation expense for the years ended December 31, 2020, 2019 and 2018 was $18.5 million, $17.8 million and $16.8 million, respectively. The total income tax benefit recognized in the consolidated statements of operations from stock-based compensation expense was $4.2 million, $3.1 million and $3.2 million for the years ended December 31, 2020, 2019 and 2018, respectively.

Restricted Stock Awards

The following table summarizes information about restricted stock awards for the year ended December 31, 2020:


Restricted Stock	Number of Shares	Weighted Average Grant-Date Fair Value
Balance at January 1, 2020	522,597	$	59.57
Granted	225,548	58.23
Vested	(208,652)	57.89
Forfeited	(45,614)	58.81
Balance at December 31, 2020	493,879	$	59.74

As of December 31, 2020, there was $19.8 million of total unrecognized compensation cost arising from restricted stock awards. This cost is expected to be recognized over a weighted average period of 2.7 years. The total fair value of restricted stock vested during 2020, 2019 and 2018 was $13.3 million, $16.8 million and $10.8 million, respectively.

Performance Stock Awards

The following table summarizes information about performance stock awards for the year ended December 31, 2020:


Performance Stock	Number of Shares	Weighted Average Grant-Date Fair Value
Balance at January 1, 2020	204,553	$	64.78
Granted	161,610	58.30
Vested	(54,377)	55.75
Forfeited	(57,337)	78.02
Balance at December 31, 2020	254,449	$	53.79

As of December 31, 2020, there was $5.1 million of total unrecognized compensation cost arising from performance stock awards whereby the performance conditions had either been met or were probable of vesting. The total fair value of performance awards vested during 2020, 2019 and 2018 was $3.5 million, $8.1 million and $1.2 million, respectively.

COMMITMENTS AND CONTINGENCIES

12 Months Ended

Dec. 31, 2020

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 government 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 waste.

At December 31, 2020 and 2019, the Company had recorded reserves of $29.8 million and $26.0 million, respectively, 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. In management's opinion, it is not reasonably possible that the potential liability beyond what has been recorded, if any, that may result from these actions, either individually or collectively, will have a material effect on our financial position, results of operations or cash flows. 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, 2020 and 2019, the $29.8 million and $26.0 million, respectively, of reserves consisted of (i) $24.0 million and $18.4 million, respectively, related to pending legal or administrative proceedings, including Superfund liabilities, which were included in remedial liabilities on the consolidated balance sheets, and (ii) $5.8 million and $7.6 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, 2020, the principal legal and administrative proceedings in which the Company was involved, or which had been terminated during 2020, 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 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, 2020 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 68 proceedings (excluding cases which have been settled but not formally dismissed) as of December 31, 2020, 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.

The Company 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. The Company 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, The Company is unable to ascertain the ultimate aggregate amount of monetary liability or financial impact with respect to these matters as of December 31, 2020. From January 1, 2020 to December 31, 2020, 12 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 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, has included 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 PRPs or potential PRPs in connection with 130 sites which are subject to or are proposed to become subject to proceedings under federal or state Superfund laws. Of the 130 Superfund related sites, five (including the BR Facility described below) involve facilities that are now owned or leased by the Company and 125 involve third-party sites to which either the Company or the prior owners of certain of the Company’s facilities shipped waste. Of the 125 third-party sites, 31 are now settled, 15 are currently requiring expenditures on remediation and 79 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 monetary liability could exceed $1.0 million at each of three of the 130 Superfund related sites.

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 completed conducting the remedial investigation and feasibility study for Devil's Swamp, at which point the feasibility study, with several remedial alternatives, was submitted to the EPA for review. During the year ended December 31, 2020, the EPA signed a Record of Decision which defines the remediation alternative selected and approved by the EPA. Based upon this Record of Decision, the Company increased the estimated remedial liability for this inactive site by $3.3 million. As of December 31, 2020, the Company has recorded its best estimate of the costs to execute upon this remediation alternative. Changes in the natural landscape and/or new information identified during the remediation could impact this estimate, but are not expected to have a future material effect on the Company's financial position, liquidity or results of operation.

Third-Party Sites. Of the 125 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 waste 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 125 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, 2020 there were no proceedings for which the Company reasonably believes that the sanctions could equal or exceed $1.0 million. 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.

Self-Insurance Liabilities

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, employee medical, 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 employee medical insurance policy is $0.8 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. We maintain umbrella insurance to limit our exposure to certain catastrophic claim costs, including general liability and vehicle claim costs. For the policy year starting in the fourth quarter of 2020, the Company changed the umbrella policy terms to include a $5.0 million annual aggregate self-insured corridor retention. At December 31, 2020 and 2019, the Company had accrued $65.6 million and $59.4 million, respectively, for its self-insurance liabilities (exclusive of employee medical insurance) using a risk-free discount rate of 0.29% and 1.52%, respectively.

Anticipated payments for contingencies related to workers' compensation, comprehensive general liability and vehicle liability related claims at December 31, 2020 for each of the next five years and thereafter were as follows (in thousands):


Years ending December 31,
2021	$	22,896
2022	13,751
2023	9,655
2024	6,448
2025	4,990
Thereafter	8,188
Undiscounted self-insurance liabilities	65,928
Less: Discount	(320)
Total self-insurance liabilities (included in accrued expenses)	$	65,608

LEASES

12 Months Ended

Dec. 31, 2020

Leases [Abstract]

LEASES

As of December 31, 2020, the Company’s lease portfolio was predominately operating leases for real estate, equipment, such as vehicles and industrial equipment utilized in operations, and rail cars. The Company presents operating lease balances separately on the consolidated balance sheet. The Company's finance leases relate to equipment, rail cars and certain real estate. The following table presents our finance lease balances and their classification on the consolidated balance sheets (in thousands):


Finance Lease Balances (Classification)	December 31, 2020		December 31, 2019
ROU assets (Property, plant and equipment, net)	$	60,271	$	32,307
Current portion of lease liabilities (Accrued expenses)	5,840		801
Long-term portion of lease liabilities (Other long-term liabilities)	55,038		34,517

The Company’s lease expense was as follows (in thousands):


	For the year ended December 31, 2020		For the year ended December 31, 2019
Operating lease cost	$	53,194	$	55,402
Finance lease cost:
Amortization of ROU assets	4,966		1,142
Interest on lease liabilities	1,523		1,415
Total finance lease cost	6,489		2,557
Short-term lease cost	70,692		84,749
Variable lease cost	3,691		6,702
Total lease cost	$	134,066	$	149,410

Rent expense, including short-term rentals for the year ended December 31, 2018, prior to the Company's adoption of ASC 842, was $141.1 million.

Other information related to leases was as follows:


Weighted Average Remaining Lease Term (years)	December 31, 2020		December 31, 2019
Operating leases	5.1		5.1
Finance leases	9.3		21.3
Weighted Average Discount Rate
Operating leases	4.89	%	5.29	%
Finance leases	3.57	%	4.97	%

The weighted average remaining lease term of the finance leases decreased significantly due to the 2020 acquisition of the Company's corporate headquarters which had previously been recognized as a finance lease.


Supplemental Cash Flow Related Disclosures (in thousands)	For the year ended December 31, 2020		For the year ended December 31, 2019
Cash paid for amounts included in the measurement of lease liabilities
Operating cash flows from operating leases	$	53,498	$	56,240
Operating cash flows from finance leases	1,523		1,415
Financing cash flows from finance leases	4,469		586
ROU assets obtained in exchange for operating lease liabilities	34,358		17,699
ROU assets obtained in exchange for finance lease liabilities	32,526		33,449

At December 31, 2020, the Company's future lease payments under non-cancelable leases that have lease terms in excess of one year were as follows (in thousands):


Years ending December 31,	December 31, 2020
	Operating Leases		Finance Leases
2021	$	45,341	$	8,407
2022	37,629		8,972
2023	29,014		8,281
2024	21,048		8,248
2025	14,672		7,573
Thereafter	25,064		31,632
Total future lease payments	172,768		73,113
Amount representing interest	(21,760)		(12,235)
Total lease liabilities	$	151,008	$	60,878

At December 31, 2020, none of the Company's executed leases that had not yet commenced will create significant rights or obligations in the future and its sublease transactions are not material. Additionally, the Company does not have any related party leases, and there were no restrictions or covenants imposed by its leases.

LEASES


Finance Lease Balances (Classification)	December 31, 2020		December 31, 2019
ROU assets (Property, plant and equipment, net)	$	60,271	$	32,307
Current portion of lease liabilities (Accrued expenses)	5,840		801
Long-term portion of lease liabilities (Other long-term liabilities)	55,038		34,517

The Company’s lease expense was as follows (in thousands):


	For the year ended December 31, 2020		For the year ended December 31, 2019
Operating lease cost	$	53,194	$	55,402
Finance lease cost:
Amortization of ROU assets	4,966		1,142
Interest on lease liabilities	1,523		1,415
Total finance lease cost	6,489		2,557
Short-term lease cost	70,692		84,749
Variable lease cost	3,691		6,702
Total lease cost	$	134,066	$	149,410

Rent expense, including short-term rentals for the year ended December 31, 2018, prior to the Company's adoption of ASC 842, was $141.1 million.

Other information related to leases was as follows:


Weighted Average Remaining Lease Term (years)	December 31, 2020		December 31, 2019
Operating leases	5.1		5.1
Finance leases	9.3		21.3
Weighted Average Discount Rate
Operating leases	4.89	%	5.29	%
Finance leases	3.57	%	4.97	%


Supplemental Cash Flow Related Disclosures (in thousands)	For the year ended December 31, 2020		For the year ended December 31, 2019
Cash paid for amounts included in the measurement of lease liabilities
Operating cash flows from operating leases	$	53,498	$	56,240
Operating cash flows from finance leases	1,523		1,415
Financing cash flows from finance leases	4,469		586
ROU assets obtained in exchange for operating lease liabilities	34,358		17,699
ROU assets obtained in exchange for finance lease liabilities	32,526		33,449

At December 31, 2020, the Company's future lease payments under non-cancelable leases that have lease terms in excess of one year were as follows (in thousands):


Years ending December 31,	December 31, 2020
	Operating Leases		Finance Leases
2021	$	45,341	$	8,407
2022	37,629		8,972
2023	29,014		8,281
2024	21,048		8,248
2025	14,672		7,573
Thereafter	25,064		31,632
Total future lease payments	172,768		73,113
Amount representing interest	(21,760)		(12,235)
Total lease liabilities	$	151,008	$	60,878

SEGMENT REPORTING

12 Months Ended

Dec. 31, 2020

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. The Company is managed and reports as two operating segments; (i) the Environmental Services segment and (ii) the Safety-Kleen segment.

Third-party revenue is revenue billed to outside customers by a particular segment. Direct revenues 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.”

The following tables reconcile third-party revenues to direct revenues for the years ended December 31, 2020, 2019 and 2018 (in thousands):


	For the year ended December 31, 2020
	Environmental Services		Safety-Kleen		Corporate Items		Totals
Third-party revenues	$	2,004,081	$	1,139,726	$	290	$	3,144,097
Intersegment revenues, net	129,666		(129,666)		—		—
Corporate Items, net	3,559		142		(3,701)		—
Direct revenues	$	2,137,306	$	1,010,202	$	(3,411)	$	3,144,097


	For the year ended December 31, 2019
	Environmental Services		Safety-Kleen		Corporate Items		Totals
Third-party revenues	$	2,092,363	$	1,318,691	$	1,136	$	3,412,190
Intersegment revenues, net	140,577		(140,577)		—		—
Corporate Items, net	4,128		15		(4,143)		—
Direct revenues	$	2,237,068	$	1,178,129	$	(3,007)	$	3,412,190


	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

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

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


	For the years ended December 31,
	2020		2019		2018
Adjusted EBITDA:
Environmental Services	$	519,960	$	446,284	$	380,856
Safety-Kleen	229,172		282,378		282,029
Corporate Items	(193,830)		(188,345)		(171,880)
Total	555,302		540,317		491,005
Reconciliation to Consolidated Statements of Operations:

Accretion of environmental liabilities	11,051		10,136		9,806
Depreciation and amortization	292,915		300,725		298,625

Income from operations	251,336		229,456		182,574
Other expense (income), net	290		(2,897)		4,510
Loss on early extinguishment of debt	—		6,131		2,488
Loss (gain) on sale of businesses	3,376		(687)		—
Interest expense, net of interest income	73,120		78,670		81,094
Income from operations before provision for income taxes	$	174,550	$	148,239	$	94,482

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


	December 31, 2020		December 31, 2019
Property, plant and equipment, net
Environmental Services	$	879,176	$	939,352
Safety-Kleen	555,894		555,310
Corporate Items	90,228		93,489
Total property, plant and equipment, net	$	1,525,298	$	1,588,151

Goodwill and Permits and other intangibles, net
Environmental Services
Goodwill	$	212,386	$	212,531
Permits and other intangibles, net	78,928		89,722
Total Environmental Services	291,314		302,253

Safety-Kleen
Goodwill	$	314,637	$	312,482
Permits and other intangibles, net	307,692		329,344
Total Safety-Kleen	622,329		641,826

Total	$	913,643	$	944,079

Geographic Information

As of December 31, 2020 and 2019, the Company had property, plant and equipment, net of depreciation and amortization and permits and other intangible assets, net of amortization in the following geographic locations (in thousands):


	December 31, 2020				December 31, 2019
	Total		% of Total		Total		% of Total
Property, plant and equipment, net
United States	$	1,246,758	81.7	%	$	1,273,205	80.2	%
Canada and other foreign	278,540		18.3		314,946		19.8
Total property, plant and equipment, net	$	1,525,298	100.0	%	$	1,588,151	100.0	%

Permits and other intangibles, net
United States	$	342,787	88.7	%	$	372,609	88.9	%
Canada and other foreign	43,833		11.3		46,457		11.1
Total permits and other intangibles, net	$	386,620	100.0	%	$	419,066	100.0	%

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


	December 31, 2020		December 31, 2019
United States	$	3,447,811	$	3,413,254
Canada and other foreign	683,709		695,650

Total	$	4,131,520	$	4,108,904

- Definition

The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 31
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8924-108599

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8981-108599

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8721-108599

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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-Paragraph 32
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
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-Paragraph 41
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9038-108599

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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-Section 50
-Paragraph 32
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-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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-Paragraph 22
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8736-108599

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
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-Paragraph 42
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8657-108599

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8721-108599

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-URI http://asc.fasb.org/topic&trid=2134510

+ Details

SCHEDULE II VALUATION AND QUALIFYING ACCOUNTS

12 Months Ended

Dec. 31, 2020

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, 2020

(in thousands)


Allowance for Doubtful Accounts	Balance Beginning of Period		Additions Charged to Operating Expense		Deductions from Reserves (1)		Balance End of Period
2018	$	16,173	$	15,817	$	5,622	$	26,368
2019	26,368		2,408		6,283		22,493
2020	22,493		10,133		7,992		24,634

___________________________________

(1) Amounts deemed uncollectible, net of recoveries.


Revenue Allowance(2)	Balance Beginning of Period		Additions Charged to Revenue		Deductions from Reserves		Balance End of Period
2018	$	11,626	$	41,338	$	35,017	$	17,947
2019	17,947		35,549		37,278		16,218
2020	16,218		45,784		41,887		20,115

___________________________________

(2) 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
2018	$	68,355	$	10,466	$	474	$	79,295
2019	79,295		4,459		(111)		83,643
2020	83,643		(11,339)		4,740		77,044

SIGNIFICANT ACCOUNTING POLICIES (Policies)

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

Principles of Consolidation

Principles of ConsolidationThe accompanying consolidated financial 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

Reclassifications

Certain prior year amounts have been reclassified to conform to the current year presentation. These reclassifications have no impact on previously reported subtotals.

Cash, Cash Equivalents and Uncashed Checks

Marketable Securities

total marketable securities and cash equivalents as follows (in thousands):


	December 31, 2020		December 31, 2019
Commercial paper	$	—	$	2,395
Total cash equivalents	—		2,395
U.S. Treasury securities	28,901		12,406
Corporate notes and bonds	22,956		26,678
Commercial paper	—		3,337

Total marketable securities	51,857		42,421
Total	$	51,857	$	44,816

Allowances for Doubtful Accounts

Credit Concentration

Inventories and Supplies

Property, Plant and Equipment, net (excluding landfill assets and finance lease right of use assets)

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

Permits and Other Intangibles

Landfill Accounting


Facility Name	Location	Remaining Lives (Years)	Permitted Remaining Highly Probable Airspace (cubic yards) (in thousands)
Buttonwillow	California	22	5,739
Deer Park	Texas	2	67
Deer Trail	Colorado	27	1,629
Grassy Mountain	Utah	41	4,710
Kimball	Nebraska	6	144
Lambton	Ontario, Canada	51	4,633
Lone Mountain	Oklahoma	32	3,803
Ryley	Alberta, Canada	5	575
Sawyer	North Dakota	68	3,416
			24,716

At December 31, 2020 and 2019, 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, 2018 through December 31, 2020 (in thousands of cubic yards):


	2020	2019	2018
Remaining capacity, beginning of year	28,494	29,760	31,113
Changes in highly probable airspace, net	(2,962)	—	(223)
Consumed	(816)	(1,266)	(1,130)
Remaining capacity, end of year	24,716	28,494	29,760

Non-Landfill Closure and Post-Closure Liabilities

Remedial Liabilities

Self Insurance Liabilities

Self-Insurance Liabilities

Revenue recognition

Revenue Recognition

The Company's Environmental Services operating segment generally has the following three sources of revenue:

The Company's Safety-Kleen operating segment generally has the following two sources of revenue:

Foreign Currency

Advertising Expense

Advertising costs are expensed as incurred. Advertising expense was $9.0 million in 2020, $9.8 million in 2019 and $10.5 million in 2018.

Stock-Based Compensation

Income Taxes

Earnings per Share ("EPS")

Leases

SIGNIFICANT ACCOUNTING POLICIES (Tables)

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

Schedule of Cash Equivalents and Marketable Securities

As of December 31, 2020 and 2019, the Company had

total marketable securities and cash equivalents as follows (in thousands):


	December 31, 2020		December 31, 2019
Commercial paper	$	—	$	2,395
Total cash equivalents	—		2,395
U.S. Treasury securities	28,901		12,406
Corporate notes and bonds	22,956		26,678
Commercial paper	—		3,337

Total marketable securities	51,857		42,421
Total	$	51,857	$	44,816

Schedule of Asset Classification and Estimated Useful Life

The Company depreciates and amortizes the capitalized 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, 2020		December 31, 2019
Land	$	139,776	$	131,023
Asset retirement costs (non-landfill)	16,407		15,924
Landfill assets	191,687		182,276
Buildings and improvements (1)	509,804		499,159
Camp equipment	159,021		158,277
Vehicles (2)	844,026		785,056
Equipment (3)	1,807,235		1,779,366
Furniture and fixtures	7,082		6,054
Construction in progress	24,378		36,679
	3,699,416		3,593,814
Less - accumulated depreciation and amortization	2,174,118		2,005,663
Total property, plant and equipment, net	$	1,525,298	$	1,588,151

___________________________________

(1) Balances inclusive of gross ROU assets classified as finance leases of $8.9 million and $31.0 million, respectively.

(2) Balances inclusive of gross ROU assets classified as finance leases of $47.2 million and $2.4 million, respectively.

(3) December 31, 2020 balance inclusive of gross ROU assets classified as finance leases of $9.3 million.

Schedule of Active Landfill Sites


Facility Name	Location	Remaining Lives (Years)	Permitted Remaining Highly Probable Airspace (cubic yards) (in thousands)
Buttonwillow	California	22	5,739
Deer Park	Texas	2	67
Deer Trail	Colorado	27	1,629
Grassy Mountain	Utah	41	4,710
Kimball	Nebraska	6	144
Lambton	Ontario, Canada	51	4,633
Lone Mountain	Oklahoma	32	3,803
Ryley	Alberta, Canada	5	575
Sawyer	North Dakota	68	3,416
			24,716

Schedule of Remaining Highly Probable Airspace

The following table presents the remaining highly probable airspace from January 1, 2018 through December 31, 2020 (in thousands of cubic yards):


	2020	2019	2018
Remaining capacity, beginning of year	28,494	29,760	31,113
Changes in highly probable airspace, net	(2,962)	—	(223)
Consumed	(816)	(1,266)	(1,130)
Remaining capacity, end of year	24,716	28,494	29,760

REVENUES (Tables)

12 Months Ended

Dec. 31, 2020

Revenue from Contract with Customer [Abstract]

Schedule of Disaggregation of Revenue


	For the year ended December 31, 2020
	Environmental Services		Safety-Kleen		Corporate		Total
Primary Geographical Markets
United States	$	1,690,256	$	1,049,975	$	(674)	$	2,739,557
Canada	313,825		89,751		964		404,540
Total third-party revenues	$	2,004,081	$	1,139,726	$	290	$	3,144,097

Sources of Revenue (1)
Technical Services	$	1,062,714	$	—	$	—	$	1,062,714
Field and Emergency Response Services	461,036		—		—		461,036
Industrial Services and Other	480,331		—		290		480,621
Safety-Kleen Environmental Services	—		809,236		—		809,236
Safety-Kleen Oil	—		330,490		—		330,490
Total third-party revenues	$	2,004,081	$	1,139,726	$	290	$	3,144,097


	For the year ended December 31, 2019
	Environmental Services		Safety-Kleen		Corporate		Total
Primary Geographical Markets
United States	$	1,721,322	$	1,220,096	$	(586)	$	2,940,832
Canada	371,041		98,595		1,722		471,358
Total third-party revenues	$	2,092,363	$	1,318,691	$	1,136	$	3,412,190

Sources of Revenue (1)
Technical Services	$	1,120,043	$	—	$	—	$	1,120,043
Field and Emergency Response Services	340,906		—		—		340,906
Industrial Services and Other (2)	631,414		—		1,136		632,550
Safety-Kleen Environmental Services	—		851,520		—		851,520
Safety-Kleen Oil	—		467,171		—		467,171
Total third-party revenues	$	2,092,363	$	1,318,691	$	1,136	$	3,412,190


	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 and Other (3)	661,728		—		1,105		662,833
Safety-Kleen Environmental Services	—		795,077		—		795,077
Safety-Kleen Oil	—		500,278		—		500,278
Total third-party revenues	$	2,003,843	$	1,295,355	$	1,105	$	3,300,303

_____________________

Schedule of Contract Balances

Contract Balances


(in thousands)	December 31, 2020		December 31, 2019
Receivables	$	611,534	$	644,738
Contract assets (unbilled receivables)	55,681		56,326
Contract liabilities (deferred revenue)	74,066		73,370

INVENTORIES AND SUPPLIES (Tables)

12 Months Ended

Dec. 31, 2020

Inventory Disclosure [Abstract]

Schedule of Inventories

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


	December 31, 2020		December 31, 2019
Oil and oil related products	$	76,209	$	75,408
Supplies and drums	120,007		115,128
Solvent and solutions	8,812		9,973
Other	15,470		14,235
Total inventories and supplies	$	220,498	$	214,744

PROPERTY, PLANT, AND EQUIPMENT (Tables)

12 Months Ended

Dec. 31, 2020

Property, Plant and Equipment [Abstract]

Schedule of Property, Plant and Equipment

The Company depreciates and amortizes the capitalized 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, 2020		December 31, 2019
Land	$	139,776	$	131,023
Asset retirement costs (non-landfill)	16,407		15,924
Landfill assets	191,687		182,276
Buildings and improvements (1)	509,804		499,159
Camp equipment	159,021		158,277
Vehicles (2)	844,026		785,056
Equipment (3)	1,807,235		1,779,366
Furniture and fixtures	7,082		6,054
Construction in progress	24,378		36,679
	3,699,416		3,593,814
Less - accumulated depreciation and amortization	2,174,118		2,005,663
Total property, plant and equipment, net	$	1,525,298	$	1,588,151

___________________________________

(1) Balances inclusive of gross ROU assets classified as finance leases of $8.9 million and $31.0 million, respectively.

(2) Balances inclusive of gross ROU assets classified as finance leases of $47.2 million and $2.4 million, respectively.

(3) December 31, 2020 balance inclusive of gross ROU assets classified as finance leases of $9.3 million.

GOODWILL AND OTHER INTANGIBLE ASSETS (Tables)

12 Months Ended

Dec. 31, 2020

Goodwill and Intangible Assets Disclosure [Abstract]

Schedule of Changes to Goodwill

The changes in goodwill for the years ended December 31, 2020 and 2019 were as follows (in thousands):


	Environmental Services		Safety-Kleen		Totals
Balance at January 1, 2019	$	207,019	$	307,170	$	514,189
Increase from current period acquisitions	7,378		5,225		12,603
Measurement period adjustments from prior period acquisitions	(2,675)		(1,355)		(4,030)


Foreign currency translation	809		1,442		2,251
Balance at December 31, 2019	$	212,531	$	312,482	$	525,013
Increase from current period acquisition	—		1,439		1,439
Measurement period adjustments from prior period acquisitions	23		—		23
Decrease from disposition of businesses	(674)		—		(674)

Foreign currency translation	506		716		1,222
Balance at December 31, 2020	$	212,386	$	314,637	$	527,023

Schedule of Finite-Lived Intangible Assets by Major Class

As of December 31, 2020 and 2019, the Company's finite-lived and indefinite-lived intangible assets consisted of the following (in thousands):


	December 31, 2020						December 31, 2019
	Cost		Accumulated Amortization		Net			Cost		Accumulated Amortization		Net
Permits	$	183,766	$	95,033	$	88,733		$	184,235	$	87,228	$	97,007
Customer and supplier relationships	382,083		211,895		170,188			401,696		207,884		193,812
Other intangible assets	39,287		34,744		4,543			38,331		33,018		5,313
Total amortizable permits and other intangible assets	605,136		341,672		263,464			624,262		328,130		296,132
Trademarks and trade names	123,156		—		123,156			122,934		—		122,934
Total permits and other intangible assets	$	728,292	$	341,672	$	386,620		$	747,196	$	328,130	$	419,066

Schedule of Indefinite-Lived Intangible Assets

As of December 31, 2020 and 2019, the Company's finite-lived and indefinite-lived intangible assets consisted of the following (in thousands):


	December 31, 2020						December 31, 2019
	Cost		Accumulated Amortization		Net			Cost		Accumulated Amortization		Net
Permits	$	183,766	$	95,033	$	88,733		$	184,235	$	87,228	$	97,007
Customer and supplier relationships	382,083		211,895		170,188			401,696		207,884		193,812
Other intangible assets	39,287		34,744		4,543			38,331		33,018		5,313
Total amortizable permits and other intangible assets	605,136		341,672		263,464			624,262		328,130		296,132
Trademarks and trade names	123,156		—		123,156			122,934		—		122,934
Total permits and other intangible assets	$	728,292	$	341,672	$	386,620		$	747,196	$	328,130	$	419,066

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, 2020 is as follows (in thousands):


Years ending December 31,	Expected Amortization
2021	$	30,163
2022	29,911
2023	25,587
2024	24,092
2025	23,121
Thereafter	130,590
	$	263,464

ACCRUED EXPENSES (Tables)

12 Months Ended

Dec. 31, 2020

Payables and Accruals [Abstract]

Schedule of Accrued Expenses

Accrued expenses consisted of the following (in thousands):


	December 31, 2020		December 31, 2019
Accrued insurance	$	77,514	$	74,376
Accrued interest	19,697		21,222
Accrued compensation and benefits	81,437		72,473
Accrued income, real estate, sales and other taxes	25,843		35,749
Interest rate swap liability	33,630		20,840
Accrued other	57,702		51,880
	$	295,823	$	276,540

CLOSURE AND POST-CLOSURE LIABILITIES (Tables)

12 Months Ended

Dec. 31, 2020

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, 2019 through December 31, 2020 were as follows (in thousands):


	Landfill Retirement Liability		Non-Landfill Retirement Liability		Total
Balance at January 1, 2019	$	37,809	$	32,122	$	69,931
Liabilities assumed in acquisitions	—		220		220

New asset retirement obligations	2,705		—		2,705

Accretion	2,772		2,829		5,601
Changes in estimates recorded to consolidated statement of operations	248		2,437		2,685
Changes in estimates recorded to consolidated balance sheet	3,303		562		3,865
Expenditures	(7,718)		(2,121)		(9,839)
Currency translation and other	282		201		483
Balance at December 31, 2019	39,401		36,250		75,651
Liabilities assumed in acquisitions	—		265		265

New asset retirement obligations	2,101		—		2,101

Accretion	3,254		3,399		6,653
Changes in estimates recorded to consolidated statement of operations	6,465		103		6,568
Changes in estimates recorded to consolidated balance sheet	481		201		682
Expenditures	(3,445)		(753)		(4,198)
Currency translation and other	155		49		204
Balance at December 31, 2020	$	48,412	$	39,514	$	87,926

Schedule of Expected Payments Related to Asset Retirement Obligations


Year ending December 31,
2021	$	14,941
2022	7,816
2023	16,181
2024	6,868
2025	5,628
Thereafter	269,477
Undiscounted closure and post-closure liabilities	320,911
Less: Discount at credit-adjusted risk-free rate	(159,164)
Less: Undiscounted estimated closure and post-closure liabilities relating to airspace not yet consumed	(73,821)
Present value of closure and post-closure liabilities	$	87,926

REMEDIAL LIABILITIES (Tables)

12 Months Ended

Dec. 31, 2020

Environmental Remediation Obligations [Abstract]

Schedule of Changes to Remedial Liabilities

The changes to remedial liabilities from January 1, 2019 through December 31, 2020 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, 2019	$	1,838	$	65,315	$	53,864	$	121,017


Accretion	88		2,639		1,808		4,535
Changes in estimates recorded to consolidated statement of operations	(17)		(913)		(2,087)		(3,017)
Expenditures	(59)		(5,079)		(3,724)		(8,862)
Currency translation and other	1		29		470		500
Balance at December 31, 2019	1,851		61,991		50,331		114,173


Accretion	90		2,607		1,701		4,398
Changes in estimates recorded to consolidated statement of operations	(15)		2,873		1,272		4,130
Expenditures	(61)		(4,332)		(3,810)		(8,203)
Currency translation and other	—		(79)		394		315
Balance at December 31, 2020	$	1,865	$	63,060	$	49,888	$	114,813

Remedial Liabilities Anticipated Payments for Each of the Next Five Years


Year ending December 31,
2021	$	12,718
2022	19,275
2023	11,420
2024	9,073
2025	6,526
Thereafter	75,915
Undiscounted remedial liabilities	134,927
Less: Discount	(20,114)
Total remedial liabilities	$	114,813

Schedule of Environmental Exit Costs by Cost

Estimates based on type of facility or site (in thousands, except percentages):


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 (37 facilities)	$	42,151	36.7	%	$	10,565
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 (27 facilities)	63,060		54.9		10,716
Superfund sites (16 sites)	9,602		8.4		960
Total	$	114,813	100.0	%	$	22,241

___________________________________

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

Estimates based on amount of potential liability (in thousands, except percentages):


Location	Type of Facility or Site	Remedial Liability(1)		% of Total		Reasonably Possible Additional Liabilities(2)
Baton Rouge, LA	Closed incinerator and landfill	$	25,650	22.3	%	$	4,208
Bridgeport, NJ	Closed incinerator	17,832		15.5		2,510
Mercier, Quebec	Idled incinerator and legal proceedings	11,158		9.7		1,157
Linden, NJ	Operating solvent recycling center	7,220		6.3		758
Various	All other incinerators, landfills, wastewater treatment facilities and service centers (60 facilities)	43,351		37.8		12,648
Various	Superfund sites (each representing less than 5% of total liabilities) (16 sites)	9,602		8.4		960
Total		$	114,813	100.0	%	$	22,241

_________________________________

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

FINANCING ARRANGEMENTS (Tables)

12 Months Ended

Dec. 31, 2020

Debt Disclosure [Abstract]

Schedule of Financing Arrangements

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


Current Debt:	December 31, 2020		December 31, 2019
Secured senior term loans ("Term Loans")	$	7,535	$	7,535


Long-Term Debt:
Secured senior Term Loans due June 30, 2024	$	719,626	$	727,162
Unsecured senior notes, at 4.875%, due July 15, 2027 ("2027 Notes")	545,000		545,000
Unsecured senior notes, at 5.125%, due July 15, 2029 ("2029 Notes")	300,000		300,000

Long-term debt, at par	1,564,626		1,572,162
Unamortized debt issuance costs and premium, net	(14,985)		(18,046)
Long-term debt, at carrying value	$	1,549,641	$	1,554,116

Schedule of Redemption Prices

2027 Notes


Year	Percentage
2022	102.438	%
2023	101.219	%
2024 and thereafter	100.000	%

2029 Notes


Year	Percentage
2024	102.563	%
2025	101.281	%
2026 and thereafter	100.000	%

- 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.

+ References

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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 9: http://fasb.org/us-gaap/role/ref/legacyRef
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-Topic 505
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-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21475-112644

+ Details

INCOME TAXES (Tables)

12 Months Ended

Dec. 31, 2020

Income Tax Disclosure [Abstract]

Schedule of Income before Income Tax, Domestic and Foreign

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


	For the years ended December 31,
	2020		2019		2018
Domestic	$	168,117	$	156,571	$	115,070
Foreign	6,433		(8,332)		(20,588)
Total	$	174,550	$	148,239	$	94,482

Schedule of Components of Provision for Income Taxes

The provision for income taxes consisted of the following (in thousands, except percentages):


	For the years ended December 31,
	2020		2019		2018
Current:
Federal	$	33,327	$	20,482	$	(7,677)
State	14,575		14,564		12,653
Foreign	1,559		7,448		4,781
	49,461		42,494		9,757
Deferred
Federal	(965)		7,933		19,899
State	(2,506)		550		(1,205)
Foreign	(6,277)		(478)		395
	(9,748)		8,005		19,089
Provision for income taxes	$	39,713	$	50,499	$	28,846

Effective tax rate	22.8%		34.1%		30.5%

Schedule of Effective Income Tax Rate Reconciliation

The Company's effective income tax rate varied from the amount computed using the statutory federal income tax rate of 21% as follows (in thousands):


	For the years ended December 31,
	2020		2019		2018
Tax expense at US statutory rate	$	36,655	$	31,130	$	19,841
State income taxes, net of federal benefit	9,837		10,597		8,711
Foreign rate differential	1,256		276		(1,124)
Valuation allowance	(11,339)		4,459		10,466


Uncertain tax position interest and penalties	(712)		474		(1,806)
Tax credits	2,039		(50)		(9,799)
Non-deductible compensation	1,406		1,922		1,813
Other	571		1,691		1,032
Adjustment for Tax Cuts and Jobs Act	—		—		(288)
Provision for income taxes	$	39,713	$	50,499	$	28,846

Schedule of Deferred Tax Assets and Liabilities

The components of the total net deferred tax assets and liabilities as of December 31, 2020 and 2019 were as follows (in thousands):


	2020		2019
Deferred tax assets:

Provision for doubtful accounts	$	10,305	$	8,949
Closure, post-closure and remedial liabilities	28,665		26,960
Operating lease liabilities	38,151		40,879
Accrued expenses	16,797		17,602
Accrued compensation and benefits	11,372		7,155
Net operating loss carryforwards(1)	50,433		50,824
Tax credit carryforwards(2)	14,471		16,909
Interest rate swap liability	10,089		6,252
Stock-based compensation	3,040		2,435
Other	5,553		8,342
Total deferred tax assets	188,876		186,307
Deferred tax liabilities:
Property, plant and equipment	(194,604)		(184,594)
Operating lease right-of-use assets	(38,018)		(40,985)
Permits and other intangible assets	(95,492)		(98,654)
Prepaid expenses	(9,660)		(9,694)
Total deferred tax liabilities	(337,774)		(333,927)
Total net deferred tax liability before valuation allowance	(148,898)		(147,620)
Less valuation allowance	(77,044)		(83,643)
Net deferred tax liabilities	$	(225,942)	$	(231,263)

___________________________________

(2)As of December 31, 2020, the foreign tax credit carryforwards of $14.1 million will expire between 2021 and 2024.

Summary of Valuation Allowance

The components of the total valuation allowance as of December 31, 2020 and 2019 were as follows (in thousands):


	2020		2019
Allowance related to:
Foreign tax credits	14,127		16,565
Acquired federal net operating losses	779		779
State net operating loss carryforwards	10,429		10,663
Foreign net operating loss carryforwards	29,839		34,149
Deferred tax assets of a Canadian subsidiary	11,468		14,922
Realized and unrealized capital losses	10,402		6,565
Total valuation allowance	$	77,044	$	83,643

Schedule of Income Tax Contingencies

The changes to unrecognized tax benefits (excluding related penalties and interest) from January 1, 2018 through December 31, 2020, were as follows (in thousands):


	2020		2019		2018
Unrecognized tax benefits, beginning of year	$	6,414	$	3,159	$	5,121

(Reductions) additions to prior year tax positions	(833)		3,354		(625)

Expirations	(203)		(209)		(1,115)

Foreign currency translation	112		110		(222)
Unrecognized tax benefits, end of year	$	5,490	$	6,414	$	3,159

EARNINGS PER SHARE (Tables)

12 Months Ended

Dec. 31, 2020

Earnings Per Share [Abstract]

Reconciliation of Basic and Diluted Earnings Per Share Computations

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


	For the years ended December 31,
	2020		2019		2018
Numerator for basic and diluted earnings per share:
Net income	$	134,837	$	97,740	$	65,636
Denominator:
Weighted basic shares outstanding	55,479		55,845		56,148
Dilutive effect of equity-based compensation awards	211		284		192
Weighted dilutive shares outstanding	55,690		56,129		56,340

Basic earnings per share	$	2.43	$	1.75	$	1.17
Diluted earnings per share	$	2.42	$	1.74	$	1.16

ACCUMULATED OTHER COMPREHENSIVE LOSS (Tables)

12 Months Ended

Dec. 31, 2020

Equity [Abstract]

Schedule of Reclassification of Accumulated Other Comprehensive Income (Loss)

The changes in accumulated other comprehensive loss by component and related tax impacts for the years ended December 31, 2020, 2019 and 2018 were as follows (in thousands):


	Foreign Currency Translation Adjustments		Unrealized (Losses) Gains on Available-for-Sale Securities		Unrealized Loss on Interest Rate Hedge		Unrealized (loss) gain on unfunded pension liability		Total
Balance at January 1, 2018	$	(170,575)	$	(146)	$	—	$	(1,686)	$	(172,407)
Other comprehensive (loss) income before reclassifications	(47,374)		182		(9,579)		124		(56,647)
Amounts reclassified out of accumulated other comprehensive loss	—		—		806		—		806
Tax benefit (expense)	5,024		(105)		—		(42)		4,877
Other comprehensive (loss) income, net of tax	(42,350)		77		(8,773)		82		(50,964)
Balance at December 31, 2018	(212,925)		(69)		(8,773)		(1,604)		(223,371)
Other comprehensive income (loss) before reclassifications	25,130		(70)		(14,401)		60		10,719
Amounts reclassified out of accumulated other comprehensive loss	—		332		2,335		—		2,667
Tax expense	—		(50)		—		(16)		(66)
Other comprehensive income (loss)	25,130		212		(12,066)		44		13,320
Balance at December 31, 2019	(187,795)		143		(20,839)		(1,560)		(210,051)
Other comprehensive income (loss) before reclassifications	10,212		(10)		(20,970)		(255)		(11,023)
Amounts reclassified out of accumulated other comprehensive loss	—		—		8,180		—		8,180
Tax benefit	1,349		2		—		66		1,417
Other comprehensive income (loss)	11,561		(8)		(12,790)		(189)		(1,426)
Balance at December 31, 2020	$	(176,234)	$	135	$	(33,629)	$	(1,749)	$	(211,477)

Reclassification out of Accumulated Other Comprehensive Income


	For the years ended December 31,
Other Comprehensive Income Components	2020		2019		2018		Location
Unrealized loss on available-for-sale securities	$	—	$	(332)	$	—	Other (expense) income, net
Unrealized loss on interest rate hedge	(8,180)		(2,335)		(806)		Interest expense, net of interest income

STOCK-BASED COMPENSATION (Tables)

12 Months Ended

Dec. 31, 2020

Share-based Payment Arrangement [Abstract]

Schedule of Restricted Stock

The following table summarizes information about restricted stock awards for the year ended December 31, 2020:


Restricted Stock	Number of Shares	Weighted Average Grant-Date Fair Value
Balance at January 1, 2020	522,597	$	59.57
Granted	225,548	58.23
Vested	(208,652)	57.89
Forfeited	(45,614)	58.81
Balance at December 31, 2020	493,879	$	59.74

Schedule of Performance Stock Awards

The following table summarizes information about performance stock awards for the year ended December 31, 2020:


Performance Stock	Number of Shares	Weighted Average Grant-Date Fair Value
Balance at January 1, 2020	204,553	$	64.78
Granted	161,610	58.30
Vested	(54,377)	55.75
Forfeited	(57,337)	78.02
Balance at December 31, 2020	254,449	$	53.79

COMMITMENTS AND CONTINGENCIES (Tables)

12 Months Ended

Dec. 31, 2020

Commitments and Contingencies Disclosure [Abstract]

Schedule of Self-Insurance Liabilities Anticipated Payments


Years ending December 31,
2021	$	22,896
2022	13,751
2023	9,655
2024	6,448
2025	4,990
Thereafter	8,188
Undiscounted self-insurance liabilities	65,928
Less: Discount	(320)
Total self-insurance liabilities (included in accrued expenses)	$	65,608

LEASES (Tables)

12 Months Ended

Dec. 31, 2020

Leases [Abstract]

Supplemental Lease Balance Sheet Information

The following table presents our finance lease balances and their classification on the consolidated balance sheets (in thousands):


Finance Lease Balances (Classification)	December 31, 2020		December 31, 2019
ROU assets (Property, plant and equipment, net)	$	60,271	$	32,307
Current portion of lease liabilities (Accrued expenses)	5,840		801
Long-term portion of lease liabilities (Other long-term liabilities)	55,038		34,517

Schedule of Lease Expense and Other Information

The Company’s lease expense was as follows (in thousands):


	For the year ended December 31, 2020		For the year ended December 31, 2019
Operating lease cost	$	53,194	$	55,402
Finance lease cost:
Amortization of ROU assets	4,966		1,142
Interest on lease liabilities	1,523		1,415
Total finance lease cost	6,489		2,557
Short-term lease cost	70,692		84,749
Variable lease cost	3,691		6,702
Total lease cost	$	134,066	$	149,410

Rent expense, including short-term rentals for the year ended December 31, 2018, prior to the Company's adoption of ASC 842, was $141.1 million.

Other information related to leases was as follows:


Weighted Average Remaining Lease Term (years)	December 31, 2020		December 31, 2019
Operating leases	5.1		5.1
Finance leases	9.3		21.3
Weighted Average Discount Rate
Operating leases	4.89	%	5.29	%
Finance leases	3.57	%	4.97	%


Supplemental Cash Flow Related Disclosures (in thousands)	For the year ended December 31, 2020		For the year ended December 31, 2019
Cash paid for amounts included in the measurement of lease liabilities
Operating cash flows from operating leases	$	53,498	$	56,240
Operating cash flows from finance leases	1,523		1,415
Financing cash flows from finance leases	4,469		586
ROU assets obtained in exchange for operating lease liabilities	34,358		17,699
ROU assets obtained in exchange for finance lease liabilities	32,526		33,449

Schedule of Operating Lease Maturity

At December 31, 2020, the Company's future lease payments under non-cancelable leases that have lease terms in excess of one year were as follows (in thousands):


Years ending December 31,	December 31, 2020
	Operating Leases		Finance Leases
2021	$	45,341	$	8,407
2022	37,629		8,972
2023	29,014		8,281
2024	21,048		8,248
2025	14,672		7,573
Thereafter	25,064		31,632
Total future lease payments	172,768		73,113
Amount representing interest	(21,760)		(12,235)
Total lease liabilities	$	151,008	$	60,878

Schedule of Finance Lease Maturity

At December 31, 2020, the Company's future lease payments under non-cancelable leases that have lease terms in excess of one year were as follows (in thousands):


Years ending December 31,	December 31, 2020
	Operating Leases		Finance Leases
2021	$	45,341	$	8,407
2022	37,629		8,972
2023	29,014		8,281
2024	21,048		8,248
2025	14,672		7,573
Thereafter	25,064		31,632
Total future lease payments	172,768		73,113
Amount representing interest	(21,760)		(12,235)
Total lease liabilities	$	151,008	$	60,878

SEGMENT REPORTING (Tables)

12 Months Ended

Dec. 31, 2020

Segment Reporting [Abstract]

Reconciliation of Third Party Revenues to Direct Revenues

The following tables reconcile third-party revenues to direct revenues for the years ended December 31, 2020, 2019 and 2018 (in thousands):


	For the year ended December 31, 2020
	Environmental Services		Safety-Kleen		Corporate Items		Totals
Third-party revenues	$	2,004,081	$	1,139,726	$	290	$	3,144,097
Intersegment revenues, net	129,666		(129,666)		—		—
Corporate Items, net	3,559		142		(3,701)		—
Direct revenues	$	2,137,306	$	1,010,202	$	(3,411)	$	3,144,097


	For the year ended December 31, 2019
	Environmental Services		Safety-Kleen		Corporate Items		Totals
Third-party revenues	$	2,092,363	$	1,318,691	$	1,136	$	3,412,190
Intersegment revenues, net	140,577		(140,577)		—		—
Corporate Items, net	4,128		15		(4,143)		—
Direct revenues	$	2,237,068	$	1,178,129	$	(3,007)	$	3,412,190


	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

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 years ended December 31,
	2020		2019		2018
Adjusted EBITDA:
Environmental Services	$	519,960	$	446,284	$	380,856
Safety-Kleen	229,172		282,378		282,029
Corporate Items	(193,830)		(188,345)		(171,880)
Total	555,302		540,317		491,005
Reconciliation to Consolidated Statements of Operations:

Accretion of environmental liabilities	11,051		10,136		9,806
Depreciation and amortization	292,915		300,725		298,625

Income from operations	251,336		229,456		182,574
Other expense (income), net	290		(2,897)		4,510
Loss on early extinguishment of debt	—		6,131		2,488
Loss (gain) on sale of businesses	3,376		(687)		—
Interest expense, net of interest income	73,120		78,670		81,094
Income from operations before provision for income taxes	$	174,550	$	148,239	$	94,482

PP&E and Intangible Assets by Segment

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


	December 31, 2020		December 31, 2019
Property, plant and equipment, net
Environmental Services	$	879,176	$	939,352
Safety-Kleen	555,894		555,310
Corporate Items	90,228		93,489
Total property, plant and equipment, net	$	1,525,298	$	1,588,151

Goodwill and Permits and other intangibles, net
Environmental Services
Goodwill	$	212,386	$	212,531
Permits and other intangibles, net	78,928		89,722
Total Environmental Services	291,314		302,253

Safety-Kleen
Goodwill	$	314,637	$	312,482
Permits and other intangibles, net	307,692		329,344
Total Safety-Kleen	622,329		641,826

Total	$	913,643	$	944,079

Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas


	December 31, 2020				December 31, 2019
	Total		% of Total		Total		% of Total
Property, plant and equipment, net
United States	$	1,246,758	81.7	%	$	1,273,205	80.2	%
Canada and other foreign	278,540		18.3		314,946		19.8
Total property, plant and equipment, net	$	1,525,298	100.0	%	$	1,588,151	100.0	%

Permits and other intangibles, net
United States	$	342,787	88.7	%	$	372,609	88.9	%
Canada and other foreign	43,833		11.3		46,457		11.1
Total permits and other intangibles, net	$	386,620	100.0	%	$	419,066	100.0	%

Schedule of Total Assets by Geographical Area

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


	December 31, 2020		December 31, 2019
United States	$	3,447,811	$	3,413,254
Canada and other foreign	683,709		695,650

Total	$	4,131,520	$	4,108,904

SIGNIFICANT ACCOUNTING POLICIES (Cash, Cash Equivalents and Uncashed Checks) (Details)	Dec. 31, 2020 USD ($)
Accounting Policies [Abstract]
Bank disbursement account balance	$ 0

SIGNIFICANT ACCOUNTING POLICIES (Marketable Securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Marketable Securities [Line Items]
Total cash equivalents	$ 0	$ 2,395
Total marketable securities	51,857	42,421
Total	51,857	44,816
U.S. Treasury securities
Marketable Securities [Line Items]
Total marketable securities	28,901	12,406
Corporate notes and bonds
Marketable Securities [Line Items]
Total marketable securities	22,956	26,678
Commercial paper
Marketable Securities [Line Items]
Total marketable securities	0	3,337
Commercial paper
Marketable Securities [Line Items]
Total cash equivalents	$ 0	$ 2,395

SIGNIFICANT ACCOUNTING POLICIES (Property, Plant and Equipment, net) (Details)	12 Months Ended
	Dec. 31, 2020
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 (Permits and Other Intangibles) (Details)	12 Months Ended
	Dec. 31, 2020
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, 2020 USD ($) cubic_yard cubicYard landfill_site	Dec. 31, 2019 USD ($) cubicYard cubic_yard	Dec. 31, 2018 USD ($) cubicYard cubic_yard
Property, Plant and Equipment [Line Items]
Landfill sites \| landfill_site	9
Permitted, but not highly probable airspace (cubic yards)	0	0
Remaining Airspace Capacity [Roll Forward]
Remaining capacity, beginning of period (cubic yards)	28,494,000	29,760,000	31,113,000
Changes in highly probable airspace, net (cubic yards)	(2,962,000)	0	(223,000)
Consumed (cubic yards)	(816,000)	(1,266,000)	(1,130,000)
Remaining capacity, end of period (cubic yards)	24,716,000	28,494,000	29,760,000
Number of landfill sites closed during period \| landfill_site	2
Landfill final closure and post-closure liabilities \| $	$ 48.4	$ 39.4
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)	5.60%	6.02%
Non-landfill closure and post-closure liabilities \| $	$ 39.5	$ 36.3
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
Buttonwillow \| California
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	22 years
Deer Park \| Texas
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	2 years
Deer Trail \| Colorado
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	27 years
Grassy Mountain \| Utah
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	41 years
Kimball \| Nebraska
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	6 years
Lambton \| Ontario, Canada
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	51 years
Lone Mountain \| Oklahoma
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	32 years
Ryley \| Alberta, Canada
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	5 years
Sawyer \| North Dakota
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	68 years
Altair
Remaining Airspace Capacity [Roll Forward]
Airspace consumed (in cubic yards) \| cubicYard	25,000	132,000	127,000
Westmorland
Remaining Airspace Capacity [Roll Forward]
Airspace consumed (in cubic yards) \| cubicYard	0	0	0
Landfill assets
Property, Plant and Equipment [Line Items]
Amortization \| $	$ 10.9	$ 12.3	$ 10.3
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	24,716,000
Permitted \| Buttonwillow \| California
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	5,739,000
Permitted \| Deer Park \| Texas
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	67,000
Permitted \| Deer Trail \| Colorado
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	1,629,000
Permitted \| Grassy Mountain \| Utah
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	4,710,000
Permitted \| Kimball \| Nebraska
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	144,000
Permitted \| Lambton \| Ontario, Canada
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	4,633,000
Permitted \| Lone Mountain \| Oklahoma
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	3,803,000
Permitted \| Ryley \| Alberta, Canada
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	575,000
Permitted \| Sawyer \| North Dakota
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	3,416,000

SIGNIFICANT ACCOUNTING POLICIES (Remedial Liabilities and Revenue Recognition) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) site numberOfSource	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Regulatory Liabilities [Line Items]
Accrual for Environmental Loss Contingencies \| $	$ 114,813	$ 114,173	$ 121,017
Period of time over which business acquisitions have been acquired (in years)	18 years
Safety-Kleen
Regulatory Liabilities [Line Items]
Number of sources of revenue	2
Environmental Services
Regulatory Liabilities [Line Items]
Number of sources of revenue	3
Minimum
Regulatory Liabilities [Line Items]
Remedial liabilities at acquisition, risk-free interest rate (as a percent)	1.37%
Maximum
Regulatory Liabilities [Line Items]
Remedial liabilities at acquisition, risk-free interest rate (as a percent)	4.90%
Superfund Proceedings
Regulatory Liabilities [Line Items]
Superfund sites \| site	130

SIGNIFICANT ACCOUNTING POLICIES (Advertising Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Advertising costs	$ 9.0	$ 9.8	$ 10.5

SIGNIFICANT ACCOUNTING POLICIES (Government Grants) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)
Accounting Policies [Abstract]
Employee retention credit under the CARES Act and the subsidy under CEWS	$ 42.3

SIGNIFICANT ACCOUNTING POLICIES (Leases) (Details)	Dec. 31, 2020
Real Estate \| Minimum
Property, Plant and Equipment [Line Items]
Lessee term	3 years
Real Estate \| Maximum
Property, Plant and Equipment [Line Items]
Lessee term	10 years
Non-Real Estate \| Minimum
Property, Plant and Equipment [Line Items]
Lessee term	2 years
Non-Real Estate \| Maximum
Property, Plant and Equipment [Line Items]
Lessee term	8 years

REVENUES (Disaggregation of Revenue) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Total revenues	$ 3,144,097	$ 3,412,190	$ 3,300,303
Technical Services
Disaggregation of Revenue [Line Items]
Total revenues	1,062,714	1,120,043	1,037,388
Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total revenues	461,036	340,906	304,727
Industrial Services and Other
Disaggregation of Revenue [Line Items]
Total revenues	480,621	632,550	662,833
Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total revenues	809,236	851,520	795,077
Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total revenues	330,490	467,171	500,278
United States
Disaggregation of Revenue [Line Items]
Total revenues	2,739,557	2,940,832	2,796,145
Canada
Disaggregation of Revenue [Line Items]
Total revenues	404,540	471,358	504,158
Environmental Services
Disaggregation of Revenue [Line Items]
Total revenues	2,137,306	2,237,068	2,141,194
Safety-Kleen
Disaggregation of Revenue [Line Items]
Total revenues	1,010,202	1,178,129	1,161,282
Operating segments \| Environmental Services
Disaggregation of Revenue [Line Items]
Total revenues	2,004,081	2,092,363	2,003,843
Operating segments \| Environmental Services \| Technical Services
Disaggregation of Revenue [Line Items]
Total revenues	1,062,714	1,120,043	1,037,388
Operating segments \| Environmental Services \| Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total revenues	461,036	340,906	304,727
Operating segments \| Environmental Services \| Industrial Services and Other
Disaggregation of Revenue [Line Items]
Total revenues	480,331	631,414	661,728
Operating segments \| Environmental Services \| Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0
Operating segments \| Environmental Services \| Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0
Operating segments \| Environmental Services \| Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Total revenues		117,000	119,800
Operating segments \| Environmental Services \| United States
Disaggregation of Revenue [Line Items]
Total revenues	1,690,256	1,721,322	1,598,402
Operating segments \| Environmental Services \| Canada
Disaggregation of Revenue [Line Items]
Total revenues	313,825	371,041	405,441
Operating segments \| Safety-Kleen
Disaggregation of Revenue [Line Items]
Total revenues	1,139,726	1,318,691	1,295,355
Operating segments \| Safety-Kleen \| Technical Services
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0
Operating segments \| Safety-Kleen \| Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0
Operating segments \| Safety-Kleen \| Industrial Services and Other
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0
Operating segments \| Safety-Kleen \| Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total revenues	809,236	851,520	795,077
Operating segments \| Safety-Kleen \| Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total revenues	330,490	467,171	500,278
Operating segments \| Safety-Kleen \| United States
Disaggregation of Revenue [Line Items]
Total revenues	1,049,975	1,220,096	1,196,661
Operating segments \| Safety-Kleen \| Canada
Disaggregation of Revenue [Line Items]
Total revenues	89,751	98,595	98,694
Corporate, non-segment
Disaggregation of Revenue [Line Items]
Total revenues	290	1,136	1,105
Corporate, non-segment \| Technical Services
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0
Corporate, non-segment \| Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0
Corporate, non-segment \| Industrial Services and Other
Disaggregation of Revenue [Line Items]
Total revenues	290	1,136	1,105
Corporate, non-segment \| Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0
Corporate, non-segment \| Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0
Corporate, non-segment \| Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Total revenues		1,100	1,100
Corporate, non-segment \| United States
Disaggregation of Revenue [Line Items]
Total revenues	(674)	(586)	1,082
Corporate, non-segment \| Canada
Disaggregation of Revenue [Line Items]
Total revenues	$ 964	$ 1,722	$ 23

REVENUES (Contract Balances) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Receivables	$ 611,534	$ 644,738
Contract assets (unbilled receivables)	55,681	56,326
Contract liabilities (deferred revenue)	$ 74,066	$ 73,370

REVENUES (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
REVENUES (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Deferred contract cost, recognition period	3 months
Deferred contracts costs	$ 22.8	$ 21.7

BUSINESS COMBINATIONS (2020 Acquisition) (Details) - USD ($) $ in Thousands		12 Months Ended
	Apr. 17, 2020	Dec. 31, 2020	Dec. 31, 2019
Business Acquisition [Line Items]
Goodwill		$ 1,439	$ 12,603
2020 Acquisitions
Business Acquisition [Line Items]
Purchase price	$ 8,800
Goodwill	$ 1,400

BUSINESS COMBINATIONS (2019 Acquisitions) (Details) - USD ($) $ in Thousands			12 Months Ended
	May 31, 2019	Mar. 01, 2019	Dec. 31, 2020	Dec. 31, 2019
Business Acquisition [Line Items]
Goodwill			$ 1,439	$ 12,603
2019 Acquisitions
Business Acquisition [Line Items]
Purchase price	$ 14,800	$ 10,400
Goodwill	$ 7,400	$ 5,200

BUSINESS COMBINATIONS (2018 Acquisitions) (Details) - USD ($) $ in Millions			12 Months Ended
	Aug. 31, 2018	Feb. 23, 2018	Dec. 31, 2018
2018 Acquisitions
Business Acquisition [Line Items]
Purchase price	$ 26.7
Veolia Business
Business Acquisition [Line Items]
Purchase price		$ 124.5
Revenue from acquisition included in the company's result of operations			$ 154.0
Pre-tax loss			0.9
Depreciation expense on property, plant and equipment			14.6
Amortization expense related to intangible assets			0.6
Acquisition-related costs			$ 1.4

INVENTORIES AND SUPPLIES (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Inventory [Line Items]
Inventories and supplies	$ 220,498	$ 214,744
Oil and oil related products
Inventory [Line Items]
Inventories and supplies	76,209	75,408
Supplies and drums
Inventory [Line Items]
Inventories and supplies	120,007	115,128
Solvent and solutions
Inventory [Line Items]
Inventories and supplies	8,812	9,973
Other
Inventory [Line Items]
Inventories and supplies	$ 15,470	$ 14,235

PROPERTY, PLANT AND EQUIPMENT - Schedule of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 3,699,416	$ 3,593,814
Less - accumulated depreciation and amortization	2,174,118	2,005,663
Total property, plant and equipment, net	1,525,298	1,588,151
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	139,776	131,023
Asset retirement costs (non-landfill)
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	16,407	15,924
Landfill assets
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	191,687	182,276
Buildings and improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	509,804	499,159
Right-of-use assets, finance leases	8,900	31,000
Camp equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	159,021	158,277
Vehicles
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	844,026	785,056
Right-of-use assets, finance leases	47,200	2,400
Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,807,235	1,779,366
Right-of-use assets, finance leases	9,300
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	7,082	6,054
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 24,378	$ 36,679

PROPERTY, PLANT AND EQUIPMENT (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Depreciation Inclusive of Amortization	$ 257.1	$ 265.5	$ 264.3

GOODWILL AND OTHER INTANGIBLE ASSETS (Changes to Goodwill) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Goodwill [Roll Forward]
Goodwill, beginning of period	$ 525,013	$ 514,189
Increase from current period acquisitions	1,439	12,603
Measurement period adjustments from prior period acquisitions	23	(4,030)
Decrease from disposition of businesses	(674)
Foreign currency translation	1,222	2,251
Goodwill, end of period	527,023	525,013
Environmental Services
Goodwill [Roll Forward]
Goodwill, beginning of period	212,531	207,019
Increase from current period acquisitions	0	7,378
Measurement period adjustments from prior period acquisitions	23	(2,675)
Decrease from disposition of businesses	(674)
Foreign currency translation	506	809
Goodwill, end of period	212,386	212,531
Safety-Kleen
Goodwill [Roll Forward]
Goodwill, beginning of period	312,482	307,170
Increase from current period acquisitions	1,439	5,225
Measurement period adjustments from prior period acquisitions	0	(1,355)
Decrease from disposition of businesses	0
Foreign currency translation	716	1,442
Goodwill, end of period	$ 314,637	$ 312,482

GOODWILL AND OTHER INTANGIBLE ASSETS (Finite-lived and Indefinite Lived Intangible Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Finite-lived intangible assets
Finite-lived intangible assets, cost	$ 605,136	$ 624,262
Accumulated Amortization	341,672	328,130
Finite-lived intangible assets, net	263,464	296,132
Total permits and other intangible assets, cost	728,292	747,196
Total permits and other intangible assets, net	386,620	419,066
Trademarks and trade names
Finite-lived intangible assets
Trademarks and trade names	123,156	122,934
Permits
Finite-lived intangible assets
Finite-lived intangible assets, cost	183,766	184,235
Accumulated Amortization	95,033	87,228
Finite-lived intangible assets, net	88,733	97,007
Customer and supplier relationships
Finite-lived intangible assets
Finite-lived intangible assets, cost	382,083	401,696
Accumulated Amortization	211,895	207,884
Finite-lived intangible assets, net	170,188	193,812
Other intangible assets
Finite-lived intangible assets
Finite-lived intangible assets, cost	39,287	38,331
Accumulated Amortization	34,744	33,018
Finite-lived intangible assets, net	$ 4,543	$ 5,313

GOODWILL AND OTHER INTANGIBLE ASSETS (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization expense of permits and other intangible assets	$ 35.8	$ 35.2	$ 34.4

GOODWILL AND OTHER INTANGIBLE ASSETS (Expected Amortization) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Expected amortization
2021	$ 30,163
2022	29,911
2023	25,587
2024	24,092
2025	23,121
Thereafter	130,590
Finite-lived intangible assets, net	$ 263,464	$ 296,132

ACCRUED EXPENSES (Schedule of Accrued Expenses) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Accrued insurance	$ 77,514	$ 74,376
Accrued interest	19,697	21,222
Accrued compensation and benefits	81,437	72,473
Accrued income, real estate, sales and other taxes	25,843	35,749
Interest rate swap liability	33,630	20,840
Accrued other	57,702	51,880
Total accrued expenses	$ 295,823	$ 276,540

ACCRUED EXPENSES (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Accrued insurance, employee medical insurance costs	$ 9.4	$ 14.3
Accrual loss for workers' compensation, comprehensive general liability and vehicle liability self-insurance programs	65.6	$ 59.4
Increase in payroll tax payable	17.0
Decrease in accrued payroll	4.8
Decrease In accrued bonuses	$ 3.5

CLOSURE AND POST-CLOSURE LIABILITIES (Changes in Post-Closure Liabilities) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) landfill_site	Dec. 31, 2019 USD ($)
Changes to post-closure liabilities
Balance at the beginning of the period	$ 75,651	$ 69,931
Liabilities assumed in acquisitions	265	220
New asset retirement obligations	2,101	2,705
Accretion	6,653	5,601
Changes in estimates recorded to consolidated statement of operations	6,568	2,685
Changes in estimates recorded to consolidated balance sheet	682	3,865
Expenditures	(4,198)	(9,839)
Currency translation and other	204	483
Balance at the end of the period	$ 87,926	75,651
Number of landfill sites closed during period \| landfill_site	2
Environmental remediation expense	$ 6,800
Increase in facility closure costs		2,300
Landfill Retirement Liability
Changes to post-closure liabilities
Balance at the beginning of the period	39,401	37,809
Liabilities assumed in acquisitions	0	0
New asset retirement obligations	2,101	2,705
Accretion	3,254	2,772
Changes in estimates recorded to consolidated statement of operations	6,465	248
Changes in estimates recorded to consolidated balance sheet	481	3,303
Expenditures	(3,445)	(7,718)
Currency translation and other	155	282
Balance at the end of the period	48,412	39,401
Non-Landfill Retirement Liability
Changes to post-closure liabilities
Balance at the beginning of the period	36,250	32,122
Liabilities assumed in acquisitions	265	220
New asset retirement obligations	0	0
Accretion	3,399	2,829
Changes in estimates recorded to consolidated statement of operations	103	2,437
Changes in estimates recorded to consolidated balance sheet	201	562
Expenditures	(753)	(2,121)
Currency translation and other	49	201
Balance at the end of the period	$ 39,514	$ 36,250

CLOSURE AND POST-CLOSURE LIABILITIES (Anticipated Payments) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Environmental Property Sale, Disposal or Abandonment Costs
2021	$ 14,941
2022	7,816
2023	16,181
2024	6,868
2025	5,628
Thereafter	269,477
Undiscounted closure and post-closure liabilities	320,911
Less: Discount at credit-adjusted risk-free rate	(159,164)
Less: Undiscounted estimated closure and post-closure liabilities relating to airspace not yet consumed	(73,821)
Present value of closure and post-closure liabilities	$ 87,926	$ 75,651	$ 69,931

REMEDIAL LIABILITIES (Changes in Remedial Liabilities) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Changes to remedial liabilities
Balance at the beginning of the period	$ 114,173	$ 121,017
Accretion	4,398	4,535
Changes in estimates recorded to consolidated statement of operations	4,130	(3,017)
Expenditures	(8,203)	(8,862)
Currency translation and other	315	500
Balance at the end of the period	114,813	114,173
Remedial Liabilities for Landfill Sites
Changes to remedial liabilities
Balance at the beginning of the period	1,851	1,838
Accretion	90	88
Changes in estimates recorded to consolidated statement of operations	(15)	(17)
Expenditures	(61)	(59)
Currency translation and other	0	1
Balance at the end of the period	1,865	1,851
Remedial Liabilities for Inactive Sites
Changes to remedial liabilities
Balance at the beginning of the period	61,991	65,315
Accretion	2,607	2,639
Changes in estimates recorded to consolidated statement of operations	2,873	(913)
Expenditures	(4,332)	(5,079)
Currency translation and other	(79)	29
Balance at the end of the period	63,060	61,991
Remedial Liabilities (Including Superfund) for Non-Landfill Operations
Changes to remedial liabilities
Balance at the beginning of the period	50,331	53,864
Accretion	1,701	1,808
Changes in estimates recorded to consolidated statement of operations	1,272	(2,087)
Expenditures	(3,810)	(3,724)
Currency translation and other	394	470
Balance at the end of the period	$ 49,888	$ 50,331

REMEDIAL LIABILITIES (Additional Information) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($) location
Site Contingency [Line Items]
Changes in estimates recorded to consolidated statement of operations	$ 4,130	$ (3,017)
Number of locations, accrual for environmental loss contingencies \| location		5
Accrual for environmental loss contingencies	5.00%
Remedial Liabilities for Inactive Sites
Site Contingency [Line Items]
Increase in estimated remedial liability	$ 3,300
Changes in estimates recorded to consolidated statement of operations	2,873	$ (913)
Remedial Liabilities for Superfund Sites
Site Contingency [Line Items]
Increase in estimated remedial liability	$ 1,800

REMEDIAL LIABILITIES (Anticipated Payments) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accrual for Environmental Loss Contingencies, Net [Abstract]
2021	$ 12,718
2022	19,275
2023	11,420
2024	9,073
2025	6,526
Thereafter	75,915
Undiscounted remedial liabilities	134,927
Less: Discount	(20,114)
Total remedial liabilities	$ 114,813	$ 114,173	$ 121,017

REMEDIAL LIABILITIES (Estimates) (Details) $ in Thousands	12 Months Ended
REMEDIAL LIABILITIES (Estimates) (Details) $ in Thousands	Dec. 31, 2020 USD ($) facility	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Site Contingency [Line Items]
Accrual for Environmental Loss Contingencies	$ 114,813	$ 114,173	$ 121,017
% of Total	100.00%
Reasonably possible additional liabilities	$ 22,241
Legal and Administrative Proceedings
Site Contingency [Line Items]
Accrual for Environmental Loss Contingencies	24,000	$ 18,400
Facilities now used in active conduct of the Company's business (37 facilities)
Site Contingency [Line Items]
Accrual for Environmental Loss Contingencies	$ 42,151
% of Total	36.70%
Reasonably possible additional liabilities	$ 10,565
Number of facility by type \| facility	37
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 (27 facilities)
Site Contingency [Line Items]
Accrual for Environmental Loss Contingencies	$ 63,060
% of Total	54.90%
Reasonably possible additional liabilities	$ 10,716
Number of facility by type \| facility	27
Superfund sites (16 sites)
Site Contingency [Line Items]
Accrual for Environmental Loss Contingencies	$ 9,602
% of Total	8.40%
Reasonably possible additional liabilities	$ 960
Number of facility by type \| facility	16
Superfund sites (16 sites) \| Various
Site Contingency [Line Items]
Accrual for Environmental Loss Contingencies	$ 9,602
% of Total	8.40%
Reasonably possible additional liabilities	$ 960
Closed incinerator and landfill \| Baton Rouge LA
Site Contingency [Line Items]
Accrual for Environmental Loss Contingencies	$ 25,650
% of Total	22.30%
Reasonably possible additional liabilities	$ 4,208
Closed incinerator \| Bridgeport, NJ
Site Contingency [Line Items]
Accrual for Environmental Loss Contingencies	$ 17,832
% of Total	15.50%
Reasonably possible additional liabilities	$ 2,510
Idled incinerator and legal proceedings \| Mercier, Quebec
Site Contingency [Line Items]
Accrual for Environmental Loss Contingencies	$ 11,158
% of Total	9.70%
Reasonably possible additional liabilities	$ 1,157
Operating solvent recycling center \| Linden, NJ
Site Contingency [Line Items]
Accrual for Environmental Loss Contingencies	$ 7,220
% of Total	6.30%
Reasonably possible additional liabilities	$ 758
All other incinerators, landfills, wastewater treatment facilities and service centers (60 facilities)
Site Contingency [Line Items]
Number of facility by type \| facility	60
All other incinerators, landfills, wastewater treatment facilities and service centers (60 facilities) \| Various
Site Contingency [Line Items]
Accrual for Environmental Loss Contingencies	$ 43,351
% of Total	37.80%
Reasonably possible additional liabilities	$ 12,648

FINANCING ARRANGEMENTS (Summary of Financing Arrangements) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Current portion of long-term debt	$ 7,535	$ 7,535
Long-term debt, at par	1,564,626	1,572,162
Unamortized debt issuance costs and premium, net	(14,985)	(18,046)
Long-term debt, at carrying value	1,549,641	1,554,116
Secured debt \| Secured senior Term Loans due June 30, 2024
Debt Instrument [Line Items]
Current portion of long-term debt	7,535	7,535
Long-term debt, at par	719,626	727,162
Unsecured debt \| Unsecured senior notes, at 4.875%, due July 15, 2027 ("2027 Notes")
Debt Instrument [Line Items]
Long-term debt, at par	$ 545,000	545,000
Interest rate (as a percent)	4.875%
Unsecured debt \| Unsecured senior notes, at 5.125%, due July 15, 2029 ("2029 Notes")
Debt Instrument [Line Items]
Long-term debt, at par	$ 300,000	$ 300,000
Interest rate (as a percent)	5.125%

FINANCING ARRANGEMENTS (Narrative) (Details) - USD ($)						12 Months Ended
FINANCING ARRANGEMENTS (Narrative) (Details) - USD ($)	Oct. 28, 2020	Mar. 31, 2020	Jul. 02, 2019	Jul. 19, 2018	Apr. 17, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Aug. 01, 2018
Financing arrangements
Loss on early extinguishment of debt						$ 0	$ 6,131,000	$ 2,488,000
Effective interest rate (as a percent)						4.67%
Fair value of long-term obligations, including current portion						$ 1,600,000,000	1,600,000,000
Borrowings from revolving credit facility						150,000,000	0	50,000,000
Revolving credit facility, available borrowing capacity						264,000,000.0
Letters of credit outstanding, amount						120,600,000
Derivative liability						$ 33,600,000	20,800,000
Secured senior Term Loans due June 30, 2024
Financing arrangements
Term loan outstanding				$ 350,000,000.0
Senior unsecured notes, at 5.25%, due August 1, 2020 (2020 Notes)
Financing arrangements
Repayments of debt				330,900,000
Accrued interest				7,900,000
Debt redemption fees				1,000,000.0
Term Loans with Interest Rate Swap Agreements
Financing arrangements
Debt outstanding								350,000,000.0
Unsecured debt
Financing arrangements
Redemption percentage of principal amount						100.00%
Debt instrument, redemption price, percentage of principal amount redeemed						35.00%
Unsecured debt \| Unsecured senior notes, at 4.875%, due July 15, 2027 ("2027 Notes")
Financing arrangements
Aggregate principal amount			$ 545,000,000.0
Redemption percentage of principal amount						104.875%
Unsecured debt \| Unsecured senior notes, at 5.125%, due July 15, 2029 ("2029 Notes")
Financing arrangements
Aggregate principal amount			300,000,000.0
Redemption percentage of principal amount						105.125%
Unsecured debt \| Unsecured senior notes, at 5.125%, due June 1, 2021 ("2021 Notes")
Financing arrangements
Repurchased amount			845,000,000.0
Repayments of debt			850,200,000
Accrued interest			$ 4,000,000.0
Unsecured debt \| Senior unsecured notes, at 5.25%, due August 1, 2020 (2020 Notes)
Financing arrangements
Repurchased amount				$ 322,000,000.0					$ 78,000,000.0
Secured debt \| Secured senior Term Loans due June 30, 2024
Financing arrangements
Effective interest rate (as a percent)						1.90%
Secured debt \| Secured senior Term Loans due June 30, 2024 \| Eurodollar
Financing arrangements
Basis spread on variable rate (as a percent)					1.75%
Secured debt \| Secured senior Term Loans due June 30, 2024 \| Base rate
Financing arrangements
Basis spread on variable rate (as a percent)					0.75%
LIne of credit
Financing arrangements
Credit facility, maximum borrowing capacity						$ 400,000,000.0
Period for measurement of average liquidity (in days)						30 days
LIne of credit \| Minimum
Financing arrangements
Commitment fee (as a percent)						0.25%
LIne of credit \| Minimum \| Base rate
Financing arrangements
Basis spread on variable rate (as a percent)						0.50%
LIne of credit \| Minimum \| LIBOR
Financing arrangements
Basis spread on variable rate (as a percent)						1.50%
LIne of credit \| Maximum
Financing arrangements
Commitment fee (as a percent)						0.375%
LIne of credit \| Maximum \| Base rate
Financing arrangements
Basis spread on variable rate (as a percent)						0.75%
LIne of credit \| Maximum \| LIBOR
Financing arrangements
Basis spread on variable rate (as a percent)						1.75%
LIne of credit \| 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%
LIne of credit \| 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%
Interest rate swap
Financing arrangements
Basis spread on variable rate (as a percent)						2.92%
Notional amount								$ 350,000,000.0
Revolving credit facility \| LIne of credit
Financing arrangements
Borrowings from revolving credit facility		$ 150,000,000.0
Debt outstanding						$ 0	$ 0
Revolving credit facility \| LIne of credit \| Parent and Domestic Subsidiaries
Financing arrangements
Credit facility, maximum borrowing capacity	$ 350,000,000.0
Revolving credit facility \| LIne of credit \| Canadian Subsidiaries
Financing arrangements
Credit facility, maximum borrowing capacity	50,000,000.0
Letters of credit \| LIne of credit \| Parent and Domestic Subsidiaries
Financing arrangements
Credit facility, maximum borrowing capacity	$ 250,000,000.0

FINANCING ARRANGEMENTS (Summary of Redemption Prices) (Details) - Unsecured debt	12 Months Ended
	Dec. 31, 2020
Debt Instrument, Redemption [Line Items]
Redemption percentage of principal amount	100.00%
Unsecured senior notes, at 4.875%, due July 15, 2027 ("2027 Notes")
Debt Instrument, Redemption [Line Items]
Redemption percentage of principal amount	104.875%
Unsecured senior notes, at 5.125%, due July 15, 2029 ("2029 Notes")
Debt Instrument, Redemption [Line Items]
Redemption percentage of principal amount	105.125%
Debt Instrument, Redemption, Period One \| Unsecured senior notes, at 4.875%, due July 15, 2027 ("2027 Notes")
Debt Instrument, Redemption [Line Items]
Redemption percentage of principal amount	102.438%
Debt Instrument, Redemption, Period One \| Unsecured senior notes, at 5.125%, due July 15, 2029 ("2029 Notes")
Debt Instrument, Redemption [Line Items]
Redemption percentage of principal amount	102.563%
Debt Instrument, Redemption, Period Two \| Unsecured senior notes, at 4.875%, due July 15, 2027 ("2027 Notes")
Debt Instrument, Redemption [Line Items]
Redemption percentage of principal amount	101.219%
Debt Instrument, Redemption, Period Two \| Unsecured senior notes, at 5.125%, due July 15, 2029 ("2029 Notes")
Debt Instrument, Redemption [Line Items]
Redemption percentage of principal amount	101.281%
Debt Instrument, Redemption, Period Three \| Unsecured senior notes, at 4.875%, due July 15, 2027 ("2027 Notes")
Debt Instrument, Redemption [Line Items]
Redemption percentage of principal amount	100.00%
Debt Instrument, Redemption, Period Three \| Unsecured senior notes, at 5.125%, due July 15, 2029 ("2029 Notes")
Debt Instrument, Redemption [Line Items]
Redemption percentage of principal amount	100.00%

INCOME TAXES (Provision for Tax Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Noncontrolling Interest [Abstract]
Domestic	$ 168,117	$ 156,571	$ 115,070
Foreign	6,433	(8,332)	(20,588)
Income before provision for income taxes	174,550	148,239	94,482
Current:
Federal	33,327	20,482	(7,677)
State	14,575	14,564	12,653
Foreign	1,559	7,448	4,781
Current income taxes	49,461	42,494	9,757
Deferred
Federal	(965)	7,933	19,899
State	(2,506)	550	(1,205)
Foreign	(6,277)	(478)	395
Deferred income taxes	(9,748)	8,005	19,089
Provision for income taxes	$ 39,713	$ 50,499	$ 28,846
Effective tax rate	22.80%	34.10%	30.50%
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Tax expense at US statutory rate	$ 36,655	$ 31,130	$ 19,841
State income taxes, net of federal benefit	9,837	10,597	8,711
Foreign rate differential	1,256	276	(1,124)
Valuation allowance	(11,339)	4,459	10,466
Uncertain tax position interest and penalties	(712)	474	(1,806)
Tax credits	2,039	(50)	(9,799)
Non-deductible compensation	1,406	1,922	1,813
Other	571	1,691	1,032
Adjustment for Tax Cuts and Jobs Act	0	0	(288)
Provision for income taxes	$ 39,713	$ 50,499	$ 28,846

INCOME TAXES (Additional Information) (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Oct. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Valuation allowance		$ 11,339	$ (4,459)	$ (10,466)
Tax benefit from analysis of certain federal manufacturing and research and development credit benefits				3,300
Additional tax credit from analysis of certain federal manufacturing and research and development credit benefits	$ 7,100
Tax credits		(2,039)	50	9,799
Tax benefits related to tax deductible foreign currency losses		1,300		5,000
Unrecognized tax benefits from transfer pricing adjustment		3,100	3,100
Unrecognized tax benefits, transfer pricing adjustments, offsetting benefit		3,100
Unrecognized tax benefits, income tax penalties and interest accrued		$ 2,100	$ 1,700	$ 800

INCOME TAXES (Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Provision for doubtful accounts	$ 10,305	$ 8,949
Closure, post-closure and remedial liabilities	28,665	26,960
Operating lease liabilities	38,151	40,879
Accrued expenses	16,797	17,602
Accrued compensation and benefits	11,372	7,155
Net operating loss carryforwards	50,433	50,824
Tax credit carryforwards	14,471	16,909
Interest rate swap liability	10,089	6,252
Stock-based compensation	3,040	2,435
Other	5,553	8,342
Total deferred tax assets	188,876	186,307
Deferred tax liabilities:
Property, plant and equipment	(194,604)	(184,594)
Operating lease right-of-use assets	(38,018)	(40,985)
Permits and other intangible assets	(95,492)	(98,654)
Prepaid expenses	(9,660)	(9,694)
Total deferred tax liabilities	(337,774)	(333,927)
Total net deferred tax liability before valuation allowance	(148,898)	(147,620)
Less valuation allowance	(77,044)	(83,643)
Net deferred tax liabilities	(225,942)	$ (231,263)
State and local operating loss carryforwards	193,200
Federal operating loss carryforwards	16,800
Foreign operating loss carryforwards	151,500
Foreign tax credit carryforwards	$ 14,100

INCOME TAXES (Valuation Allowance) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Valuation allowance, foreign tax credits	$ 14,127	$ 16,565
Valuation allowance, acquired federal net operating losses	779	779
Valuation allowance, state net operating loss carryforwards	10,429	10,663
Valuation allowance, foreign net operating loss carryforwards	29,839	34,149
Valuation allowance, deferred tax assets of a Canadian subsidiary	11,468	14,922
Valuation allowance, realized and unrealized capital losses	10,402	6,565
Valuation allowance	$ 77,044	$ 83,643

INCOME TAXES (Unrecognized Tax Benefits) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits, beginning of year	$ 6,414	$ 3,159	$ 5,121
Additions to prior year tax positions		3,354
Reductions to prior year tax positions	(833)		(625)
Expirations	(203)	(209)	(1,115)
Foreign currency translation	112	110	(222)
Unrecognized tax benefits, end of year	$ 5,490	$ 6,414	$ 3,159

EARNINGS PER SHARE (Reconciliation of Basic and Diluted Earnings Per Share Computations) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator for basic and diluted earnings per share:
Net income	$ 134,837	$ 97,740	$ 65,636
Denominator:
Weighted basic shares outstanding (in shares)	55,479	55,845	56,148
Dilutive effect of equity-based compensation awards (in shares)	211	284	192
Weighted dilutive shares outstanding (in shares)	55,690	56,129	56,340
Basic earnings per share (in dollars per share)	$ 2.43	$ 1.75	$ 1.17
Diluted earnings per share (in dollars per share)	$ 2.42	$ 1.74	$ 1.16

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22583-107794

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(19))
-URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 11
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22694-107794

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(11))
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- 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.

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+ Details

EARNINGS PER SHARE (Anti-Dilutive Securities) (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
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)	53,667	122,785	79,390
Restricted Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	8,878	16,304	121,803

STOCKHOLDERS' EQUITY (Details) - USD ($) shares in Millions	12 Months Ended
STOCKHOLDERS' EQUITY (Details) - USD ($) shares in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Equity [Abstract]
Stock repurchase program, authorized amount	$ 600,000,000.0
Repurchase of common stock (in shares)	1.2	0.3	0.8
Repurchases of common stock	$ 74,844,000	$ 21,390,000	$ 45,080,000
Stock repurchase program, remaining authorized repurchase amount	$ 209,900,000

ACCUMULATED OTHER COMPREHENSIVE LOSS (Components of AOCI) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Increase (Decrease) in Equity
Beginning balance	$ 1,269,813	$ 1,169,756	$ 1,188,202
Other comprehensive income (loss) before reclassifications	(11,023)	10,719	(56,647)
Amounts reclassified out of accumulated other comprehensive loss	8,180	2,667	806
Tax benefit (expense)	1,417	(66)	4,877
Other comprehensive (loss) income, net of tax	(1,426)	13,320	(50,964)
Ending balance	1,341,551	1,269,813	1,169,756
Foreign Currency Translation Adjustments
Increase (Decrease) in Equity
Beginning balance	(187,795)	(212,925)	(170,575)
Other comprehensive income (loss) before reclassifications	10,212	25,130	(47,374)
Amounts reclassified out of accumulated other comprehensive loss	0	0	0
Tax benefit (expense)	1,349	0	5,024
Other comprehensive (loss) income, net of tax	11,561	25,130	(42,350)
Ending balance	(176,234)	(187,795)	(212,925)
Unrealized (Losses) Gains on Available-for-Sale Securities
Increase (Decrease) in Equity
Beginning balance	143	(69)	(146)
Other comprehensive income (loss) before reclassifications	(10)	(70)	182
Amounts reclassified out of accumulated other comprehensive loss	0	332	0
Tax benefit (expense)	2	(50)	(105)
Other comprehensive (loss) income, net of tax	(8)	212	77
Ending balance	135	143	(69)
Unrealized Loss on Interest Rate Hedge
Increase (Decrease) in Equity
Beginning balance	(20,839)	(8,773)	0
Other comprehensive income (loss) before reclassifications	(20,970)	(14,401)	(9,579)
Amounts reclassified out of accumulated other comprehensive loss	8,180	2,335	806
Tax benefit (expense)	0	0	0
Other comprehensive (loss) income, net of tax	(12,790)	(12,066)	(8,773)
Ending balance	(33,629)	(20,839)	(8,773)
Unrealized (loss) gain on unfunded pension liability
Increase (Decrease) in Equity
Beginning balance	(1,560)	(1,604)	(1,686)
Other comprehensive income (loss) before reclassifications	(255)	60	124
Amounts reclassified out of accumulated other comprehensive loss	0	0	0
Tax benefit (expense)	66	(16)	(42)
Other comprehensive (loss) income, net of tax	(189)	44	82
Ending balance	(1,749)	(1,560)	(1,604)
Accumulated Other Comprehensive Loss
Increase (Decrease) in Equity
Beginning balance	(210,051)	(223,371)	(172,407)
Other comprehensive (loss) income, net of tax	(1,426)	13,320	(50,964)
Ending balance	$ (211,477)	$ (210,051)	$ (223,371)

ACCUMULATED OTHER COMPREHENSIVE LOSS (Reclassification out of AOCI) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other (expense) income, net	$ (290)	$ 2,897	$ (4,510)
Interest expense, net of interest income	73,120	78,670	81,094
Unrealized (Losses) Gains on Available-for-Sale Securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other (expense) income, net	0	(332)	0
Unrealized Loss on Interest Rate Hedge
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest expense, net of interest income	$ (8,180)	$ (2,335)	$ (806)

STOCK-BASED COMPENSATION (Stock-Based Compensation) (Details) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jun. 03, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 18.5	$ 17.8	$ 16.8
Total income tax benefit from stock-based compensation	$ 4.2	$ 3.1	$ 3.2
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period (in years)	3 years	3 years
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period (in years)	5 years	5 years
2020 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized (in shares)				2.5

STOCK-BASED COMPENSATION (Restricted Stock Awards) (Details) - Restricted Stock - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Number of Shares
Unvested, beginning of period (in shares)	522,597
Granted (in shares)	225,548
Vested (in shares)	(208,652)
Forfeited (in shares)	(45,614)
Unvested, end of period (in shares)	493,879	522,597
Weighted Average Grant-Date Fair Value
Unvested, beginning of period (in dollars per share)	$ 59.57
Granted (in dollars per share)	58.23
Vested (in dollars per share)	57.89
Forfeited (in dollars per share)	58.81
Unvested, end of period (in dollars per share)	$ 59.74	$ 59.57
Total unrecognized compensation cost	$ 19.8
Expected to be recognized over a weighted average period	2 years 8 months 12 days
Fair value of awards vested in period	$ 13.3	$ 16.8	$ 10.8

STOCK-BASED COMPENSATION (Performance Stock Awards) (Details) - Performance Stock Awards - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Number of Shares
Unvested, beginning of period (in shares)	204,553
Granted (in shares)	161,610
Vested (in shares)	(54,377)
Forfeited (in shares)	(57,337)
Unvested, end of period (in shares)	254,449	204,553
Weighted Average Grant-Date Fair Value
Unvested, beginning of period (in dollars per share)	$ 64.78
Granted (in dollars per share)	58.30
Vested (in dollars per share)	55.75
Forfeited (in dollars per share)	78.02
Unvested, end of period (in dollars per share)	$ 53.79	$ 64.78
Total unrecognized compensation cost	$ 5.1
Fair value of awards vested in period	$ 3.5	$ 8.1	$ 1.2

COMMITMENTS AND CONTINGENCIES (Legal and Administrative Proceedings) (Details) $ in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) proceeding claim	Dec. 31, 2012 CAD ($)	Dec. 31, 1999 municipality	Dec. 31, 1968 permit	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Legal and Administrative Proceedings
Reserves	$ 29,800				$ 26,000
Remedial liabilities	$ 114,813				114,173	$ 121,017
Safety-Kleen
Legal and Administrative Proceedings
Number of proceedings \| proceeding	68
Loss contingency, claims settled and dismissed, claims \| claim	12
Legal and Administrative Proceedings
Legal and Administrative Proceedings
Remedial liabilities	$ 24,000				18,400
Federal, State, and Provincial Enforcement Actions
Legal and Administrative Proceedings
Reserves relating to legal and administrative proceedings	$ 5,800				$ 7,600
Number of proceedings \| proceeding	0
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

COMMITMENTS AND CONTINGENCIES (Superfund Proceedings) (Details)	12 Months Ended
	Dec. 31, 2020 USD ($) site
Remedial Liabilities for Inactive Sites
Superfund Proceedings
Increase in estimated remedial liability \| $	$ 3,300,000
Superfund Proceedings
Superfund Proceedings
Number of sites subject to proceedings under federal or state superfund laws	130
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	125
Number of sites for which environmental remediation expense is settled	31
Third party sites requiring expenditure on remediation	15
Number of sites for which environmental remediation expense is not required	79
Loss contingency, liability limit amount \| $	$ 1,000,000.0
Number of sites which potential liability could exceed $1.0 million	3
Notices received from owners of third party sites seeking indemnification from the company	6
BR Facility \| Remedial Liabilities for Inactive Sites
Superfund Proceedings
Increase in estimated remedial liability \| $	$ 3,300,000
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, 2020 USD ($) proceeding
Federal and State Enforcement Actions
Number of proceedings \| proceeding	0
Loss contingency, liability limit amount \| $	$ 1,000,000.0

COMMITMENTS AND CONTINGENCIES (Self Insurance Liabilities) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Product Liability Contingency [Line Items]
Retention for environmental impairment		$ 1,000
Annual aggregate self-insured corridor retention amount	$ 5,000
Self-Insurance Liabilities		$ 65,600	$ 59,400
Weighted average risk free discount rate for self insurance liabilities		0.29%	1.52%
Self Insurance Losses Expected [Abstract]
2021	22,896	$ 22,896
2022	13,751	13,751
2023	9,655	9,655
2024	6,448	6,448
2025	4,990	4,990
Thereafter	8,188	8,188
Undiscounted self-insurance liabilities	65,928	65,928
Less: Discount	(320)	(320)
Total self-insurance liabilities (included in accrued expenses)	$ 65,608	65,608
Minimum
Product Liability Contingency [Line Items]
Deductible medical insurance policy		800
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

LEASES (Supplemental Finance Lease Balance Sheet information) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
ROU assets:
Finance lease (included in property, plant and equipment, net)	$ 60,271	$ 32,307
Current portion of lease liabilities:
Finance lease (included in accrued expenses)	$ 5,840	$ 801
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:AccruedLiabilitiesCurrent	us-gaap:AccruedLiabilitiesCurrent
Long-term portion of lease liabilities:
Finance lease (included in deferred taxes, unrecognized tax benefits and other long-term liabilities)	$ 55,038	$ 34,517
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesNoncurrent	us-gaap:OtherLiabilitiesNoncurrent

LEASES (Lease Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
LEASES (Lease Expense) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Operating lease cost	$ 53,194	$ 55,402
Finance lease cost:
Amortization of ROU assets	4,966	1,142
Interest on lease liabilities	1,523	1,415
Total finance lease cost	6,489	2,557
Short-term lease cost	70,692	84,749
Variable lease cost	3,691	6,702
Total lease cost	$ 134,066	$ 149,410

LEASES (Narrative) (Details) $ in Millions	12 Months Ended
LEASES (Narrative) (Details) $ in Millions	Dec. 31, 2018 USD ($)
Leases [Abstract]
Rent expense	$ 141.1

LEASES (Other Information related to Leases) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Weighted Average Remaining Lease Term (years)
Operating lease (in years)	5 years 1 month 6 days	5 years 1 month 6 days
Finance lease (in years)	9 years 3 months 18 days	21 years 3 months 18 days
Weighted Average Discount Rate
Operating lease (as a percentage)	4.89%	5.29%
Finance lease (as a percentage)	3.57%	4.97%
Cash paid for amounts included in the measurement of lease liabilities
Operating cash flows from operating leases	$ 53,498	$ 56,240
Operating cash flows from finance leases	1,523	1,415
Financing cash flows from finance leases	4,469	586	$ 0
ROU assets obtained in exchange for operating lease liabilities	34,358	17,699
ROU assets obtained in exchange for finance lease liabilities	$ 32,526	$ 33,449

LEASES (Schedule of Future Lease Payments) (Details) $ in Thousands	Dec. 31, 2020 USD ($)
Operating Leases
2021	$ 45,341
2022	37,629
2023	29,014
2024	21,048
2025	14,672
Thereafter	25,064
Total future lease payments	172,768
Amount representing interest	(21,760)
Total lease liabilities	151,008
Finance Leases
2021	8,407
2022	8,972
2023	8,281
2024	8,248
2025	7,573
Thereafter	31,632
Total future lease payments	73,113
Amount representing interest	(12,235)
Total lease liabilities	$ 60,878

SEGMENT REPORTING (Narrative) (Details)	12 Months Ended
SEGMENT REPORTING (Narrative) (Details)	Dec. 31, 2020 segment
Segment Reporting [Abstract]
Number of operating segments	2

SEGMENT REPORTING (Segment Information, Revenues, EBITA, and Reconciliation to the Consolidated Statement of Operations) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Total revenues	$ 3,144,097	$ 3,412,190	$ 3,300,303
Adjusted EBITDA	555,302	540,317	491,005
Reconciliation to Consolidated Statements of Operations:
Accretion of environmental liabilities	11,051	10,136	9,806
Depreciation and amortization	292,915	300,725	298,625
Income from operations	251,336	229,456	182,574
Other expense (income), net	290	(2,897)	4,510
Loss on early extinguishment of debt	0	6,131	2,488
Loss (gain) on sale of businesses	3,376	(687)	0
Interest expense, net of interest income	73,120	78,670	81,094
Income before provision for income taxes	174,550	148,239	94,482
Property, plant and equipment, net	1,525,298	1,588,151
Goodwill	527,023	525,013	514,189
Permits and other intangibles, net	386,620	419,066
Permits and other intangibles, net	913,643	944,079
Environmental Services
Segment Reporting Information [Line Items]
Total revenues	2,137,306	2,237,068	2,141,194
Reconciliation to Consolidated Statements of Operations:
Goodwill	212,386	212,531	207,019
Safety-Kleen
Segment Reporting Information [Line Items]
Total revenues	1,010,202	1,178,129	1,161,282
Reconciliation to Consolidated Statements of Operations:
Goodwill	314,637	312,482	307,170
Operating segments \| Environmental Services
Segment Reporting Information [Line Items]
Total revenues	2,004,081	2,092,363	2,003,843
Adjusted EBITDA	519,960	446,284	380,856
Reconciliation to Consolidated Statements of Operations:
Property, plant and equipment, net	879,176	939,352
Goodwill	212,386	212,531
Permits and other intangibles, net	78,928	89,722
Permits and other intangibles, net	291,314	302,253
Operating segments \| Safety-Kleen
Segment Reporting Information [Line Items]
Total revenues	1,139,726	1,318,691	1,295,355
Adjusted EBITDA	229,172	282,378	282,029
Reconciliation to Consolidated Statements of Operations:
Property, plant and equipment, net	555,894	555,310
Goodwill	314,637	312,482
Permits and other intangibles, net	307,692	329,344
Permits and other intangibles, net	622,329	641,826
Intersegment revenues, net \| Environmental Services
Segment Reporting Information [Line Items]
Total revenues	129,666	140,577	134,104
Intersegment revenues, net \| Safety-Kleen
Segment Reporting Information [Line Items]
Total revenues	(129,666)	(140,577)	(134,104)
Corporate Items, net
Segment Reporting Information [Line Items]
Total revenues	(3,701)	(4,143)	(3,278)
Corporate Items, net \| Environmental Services
Segment Reporting Information [Line Items]
Total revenues	3,559	4,128	3,247
Corporate Items, net \| Safety-Kleen
Segment Reporting Information [Line Items]
Total revenues	142	15	31
Corporate Items
Segment Reporting Information [Line Items]
Total revenues	290	1,136	1,105
Adjusted EBITDA	(193,830)	(188,345)	(171,880)
Reconciliation to Consolidated Statements of Operations:
Property, plant and equipment, net	90,228	93,489
Operating segments and corporate non segment
Segment Reporting Information [Line Items]
Total revenues	$ (3,411)	$ (3,007)	$ (2,173)

SEGMENT REPORTING (Geographical Information) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 1,525,298	$ 1,588,151
Percent of property, plant and equipment, net	100.00%	100.00%
Permits and other intangibles, net	$ 386,620	$ 419,066
Percent of permits and other intangibles, net	100.00%	100.00%
Assets	$ 4,131,520	$ 4,108,904
United States
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 1,246,758	$ 1,273,205
Percent of property, plant and equipment, net	81.70%	80.20%
Permits and other intangibles, net	$ 342,787	$ 372,609
Percent of permits and other intangibles, net	88.70%	88.90%
Assets	$ 3,447,811	$ 3,413,254
Canada
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 278,540	$ 314,946
Percent of property, plant and equipment, net	18.30%	19.80%
Permits and other intangibles, net	$ 43,833	$ 46,457
Percent of permits and other intangibles, net	11.30%	11.10%
Assets	$ 683,709	$ 695,650

- Definition

Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(11))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(g)(1)(ii))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (bb)
-URI http://asc.fasb.org/extlink&oid=121559654&loc=d3e5710-111685

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 25
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=116870748&loc=SL6758485-165988

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8736-108599

Reference 8: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(12))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 30
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8906-108599

+ Details

SCHEDULE II VALUATION AND QUALIFYING ACCOUNTS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Allowance for Doubtful Accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance Beginning of Period	$ 22,493	$ 26,368	$ 16,173
Additions Charged to Operating Expense	10,133	2,408	15,817
Deductions from Reserves	7,992	6,283	5,622
Balance End of Period	24,634	22,493	26,368
Revenue Allowance
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance Beginning of Period	16,218	17,947	11,626
Additions Charged to Operating Expense	45,784	35,549	41,338
Deductions from Reserves	41,887	37,278	35,017
Balance End of Period	20,115	16,218	17,947
Valuation Allowance on Deferred Tax Assets
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance Beginning of Period	83,643	79,295	68,355
Additions Charged to Operating Expense	(11,339)	4,459	10,466
Deductions from Reserves	4,740	(111)	474
Balance End of Period	$ 77,044	$ 83,643	$ 79,295