DOCUMENT AND ENTITY INFORMATION - shares	3 Months Ended
DOCUMENT AND ENTITY INFORMATION - shares	Mar. 31, 2018	Apr. 27, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	CLEAN HARBORS INC
Entity Central Index Key	0000822818
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding		56,189,898

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 186,352	$ 319,399
Short-term marketable securities	37,792	38,179
Accounts receivable, net of allowances aggregating $29,145 and $27,799, respectively	551,841	528,924
Unbilled accounts receivable	63,375	35,922
Deferred costs	20,847	20,445
Inventories and supplies	181,438	176,012
Prepaid expenses and other current assets	38,177	35,175
Total current assets	1,079,822	1,154,056
Property, plant and equipment, net	1,631,648	1,587,365
Other assets:
Goodwill	492,705	478,523
Permits and other intangibles, net	464,635	469,128
Other	16,006	17,498
Total other assets	973,346	965,149
Total assets	3,684,816	3,706,570
Current liabilities:
Current portion of long-term obligations	4,000	4,000
Accounts payable	237,953	224,231
Deferred revenue	68,748	67,822
Accrued expenses	194,160	187,982
Current portion of closure, post-closure and remedial liabilities	19,823	19,782
Total current liabilities	524,684	503,817
Other liabilities:
Closure and post-closure liabilities, less current portion of $5,519 and $6,444, respectively	58,561	54,593
Remedial liabilities, less current portion of $14,304 and $13,338, respectively	108,143	111,130
Long-term obligations, less current portion	1,625,259	1,625,537
Deferred taxes, unrecognized tax benefits and other long-term liabilities	222,643	223,291
Total other liabilities	2,014,606	2,014,551
Commitments and contingent liabilities (See Note 16)
Stockholders’ equity:
Authorized 80,000,000; shares issued and outstanding 56,244,601 and 56,501,190 shares, respectively	562	565
Additional paid-in capital	675,230	686,962
Accumulated other comprehensive loss	(189,153)	(172,407)
Accumulated earnings	658,887	673,082
Total stockholders’ equity	1,145,526	1,188,202
Total liabilities and stockholders’ equity	$ 3,684,816	$ 3,706,570

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Account receivable, allowances aggregating	$ 29,145	$ 27,799
Closure and post-closure liabilities, current portion	5,519	6,444
Remedial liabilities, current portion	$ 14,304	$ 13,338
Common stock, par value (in USD per share)	$ 0.01	$ 0.01
Common stock, authorized shares (in shares)	80,000,000	80,000,000
Common stock, issued shares (in shares)	56,244,601	56,501,190
Common stock, outstanding shares (in shares)	56,244,601	56,501,190

UNAUDITED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenues:
Service revenues	$ 619,719	$ 560,214
Product revenues	130,059	128,727
Total revenues	749,778	688,941
Cost of revenues: (exclusive of items shown separately below)
Service revenues	447,649	391,087
Product revenues	98,776	105,498
Total cost of revenues	546,425	496,585
Selling, general and administrative expenses	115,088	112,221
Accretion of environmental liabilities	2,430	2,290
Depreciation and amortization	74,844	72,412
Income from operations	10,991	5,433
Other expense, net	(299)	(1,549)
Interest expense, net of interest income of $764 and $215, respectively	(20,270)	(22,576)
(Loss) income before (benefit) provision for income taxes	(9,578)	(18,692)
Provision for income taxes	3,053	2,701
Net loss	$ (12,631)	$ (21,393)
Loss per share:
Basic (in USD per share)	$ (0.22)	$ (0.37)
Diluted (in USD per share)	$ (0.22)	$ (0.37)
Shares used to compute loss per share - Basic (in shares)	56,457	57,262
Shares used to compute loss per share - Diluted (in shares)	56,457	57,262

UNAUDITED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net loss	$ (12,631)	$ (21,393)
Other comprehensive (loss) income:
Unrealized (losses) gains on available-for-sale securities (net of tax of $80 and $152, respectively)	(195)	82
Reclassification adjustment for losses on available-for-sale securities included in net income (net of taxes of $0 and $0, respectively)	0	146
Foreign currency translation adjustments	(16,551)	5,823
Other comprehensive (loss) income	(16,746)	6,051
Comprehensive loss	$ (29,377)	$ (15,342)

UNAUDITED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Unrealized gains (losses) on available-for-sale securities, taxes	$ 80	$ 152
Reclassification adjustment for gains on available-for-sale securities included in net (loss) income taxes	$ 0	$ 0

UNAUDITED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities:
Net loss	$ (12,631)	$ (21,393)
Adjustments to reconcile net loss to net cash from operating activities:
Depreciation and amortization	74,844	72,412
Allowance for doubtful accounts	2,303	1,935
Amortization of deferred financing costs and debt discount	916	829
Accretion of environmental liabilities	2,430	2,290
Changes in environmental liability estimates	(562)	102
Deferred income taxes	(5)	196
Stock-based compensation	3,077	2,271
Other expense, net	299	1,549
Environmental expenditures	(2,425)	(2,938)
Changes in assets and liabilities, net of acquisitions
Accounts receivable and unbilled accounts receivable	(14,769)	24,301
Inventories and supplies	(5,625)	(2,676)
Other current assets	(2,923)	(1,277)
Accounts payable	9,714	(13,609)
Other current and long-term liabilities	(2,740)	(6,873)
Net cash from operating activities	51,903	57,119
Cash flows used in investing activities:
Additions to property, plant and equipment	(44,242)	(42,462)
Proceeds from sale and disposal of fixed assets	798	1,030
Acquisitions, net of cash acquired	(120,000)	(11,946)
Proceeds from sale of business	0	2,018
Additions to intangible assets, including costs to obtain or renew permits	(1,245)	(751)
Proceeds from sale of available-for-sale securities	3,264	243
Purchases of available-for-sale securities	(3,003)	0
Net cash used in investing activities	(164,428)	(51,868)
Cash flows used in financing activities:
Change in uncashed checks	(3,843)	(7,557)
Proceeds from exercise of stock options	0	46
Tax payments related to withholdings on vested restricted stock	(548)	(1,021)
Repurchases of common stock	(14,264)	(6,796)
Deferred financing costs paid	0	(108)
Principal payment on debt	(1,000)	0
Net cash used in financing activities	(19,655)	(15,436)
Effect of exchange rate change on cash	(867)	554
Decrease in cash and cash equivalents	(133,047)	(9,631)
Cash and cash equivalents, beginning of period	319,399	306,997
Cash and cash equivalents, end of period	186,352	297,366
Cash payments for interest and income taxes:
Interest paid	14,676	21,717
Income taxes paid	1,999	5,519
Non-cash investing activities:
Property, plant and equipment accrued	17,911	19,270
Receivable for estimated purchase price adjustment	$ 0	$ 1,972

UNAUDITED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - 3 months ended Mar. 31, 2018 - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Earnings
Balance at beginning of period at Dec. 31, 2017	$ 1,188,202	$ 565	$ 686,962	$ (172,407)	$ 673,082
Balance beginning of period (in shares) at Dec. 31, 2017		56,501
Increase (Decrease) in Stockholders' Equity
Net loss	(12,631)				(12,631)
Other comprehensive loss	(16,746)			(16,746)
Stock-based compensation	3,077		3,077
Issuance of restricted shares, net of shares remitted and tax withholdings	(548)	$ 0	(548)
Issuance of restricted shares, net of shares remitted and tax withholdings (in shares)		24
Repurchases of common stock	$ (14,264)	$ (3)	(14,261)
Repurchases of common stock (in shares)	(300)	(280)
Balance at end of period at Mar. 31, 2018	$ 1,145,526	$ 562	$ 675,230	$ (189,153)	658,887
Balance ending of period (in shares) at Mar. 31, 2018		56,245
Increase (Decrease) in Stockholders' Equity
Cumulative effect of change in accounting principle	$ (1,564)
Cumulative effect of change in accounting principle \| Accounting Standards Update 2016-16					$ (1,564)

BASIS OF PRESENTATION	3 Months Ended
BASIS OF PRESENTATION	Mar. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
BASIS OF PRESENTATION	BASIS OF PRESENTATION The accompanying consolidated interim financial statements are unaudited and include the accounts of Clean Harbors, Inc. and its subsidiaries (collectively, “Clean Harbors,” the “Company” or "we") and have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”) and, in the opinion of management, include all adjustments which are of a normal recurring nature, necessary for a fair presentation of the financial position, results of operations, and cash flows for the periods presented. Management has made estimates and assumptions affecting the amounts reported in the Company's consolidated interim financial statements and accompanying footnotes, actual results could differ from those estimates and judgments. The results for interim periods are not necessarily indicative of results for the entire year or any other interim periods. The financial statements presented herein should be read in connection with the financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017, which includes the audited consolidated balance sheet as of December 31, 2017 from which the one presented herein was derived.

SIGNIFICANT ACCOUNTING POLICIES	3 Months Ended
SIGNIFICANT ACCOUNTING POLICIES	Mar. 31, 2018
Accounting Policies [Abstract]
SIGNIFICANT ACCOUNTING POLICIES	SIGNIFICANT ACCOUNTING POLICIES The Company's significant accounting policies are described in Note 2, "Significant Accounting Policies," in the Company's Annual Report on Form 10-K for the year ended December 31, 2017. There have been no material changes in these policies or their application except for the changes described below. Reclassifications During the first quarter of fiscal year 2018, certain of the Company's businesses undertook a reorganization which included changes to the underlying business and management structures. The reorganization resulted in combining the Environmental Services businesses from an operational and management perspective and is expected to deepen customer relationships and allow for efficiencies across the Company's operations through the sharing of resources, namely labor and equipment which will reduce third party spend and promote the cross selling of such business offerings. In connection with this reorganization, the Company’s chief operating decision maker also requested changes in the information that he regularly reviews for purposes of allocating resources and assessing performance. These changes required a reconsideration of the Company’s operating segments in the first quarter of 2018 and resulted in a change in the Company’s assessment of its operating segments. Upon reconsideration of the identification of the Company’s operating segments, the Company concluded that there are now two operating segments for disclosure in accordance with ASC 280 Segment reporting; (i) the Environmental Services segment which consists of the Company’s historical Technical Services, Industrial Services, Field Services and Oil, Gas and Lodging businesses and (ii) the Safety-Kleen segment. See Note 18, "Segment Reporting," for more information. The amounts presented for the three months ended March 31, 2017 have been recast to reflect the impact of such changes. These reclassifications and adjustments had no effect on consolidated statements of operations, consolidated statements of comprehensive loss, consolidated statements of cash flows or consolidated statements of stockholders' equity for any of the periods presented. Recent Accounting Pronouncements Standards implemented In May 2014, the Financial Accounting Standards Board ("FASB") issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606), which replaces numerous requirements in U.S. GAAP, including industry-specific requirements, and provides companies with a single revenue recognition model for recognizing revenue from contracts with customers. The guidance permits two methods of adoption: retrospectively to each prior reporting period presented (full retrospective method), or retrospectively with the cumulative effect of initially applying the guidance recognized at the date of initial application (the modified retrospective method). On January 1, 2018, the Company adopted Topic 606 using the modified retrospective method for all contracts. Results for reporting periods beginning on the date of adoption are presented under ASC 606, while prior period amounts have not been adjusted and continue to be reported in accordance with the Company's historical accounting methodology pursuant to ASC 605, Revenue Recognition (“ASC 605”). Upon adoption, a cumulative effect adjustment was not required as the majority of the Company’s contracts are recognized based on time and materials incurred and were not impacted by the new guidance. The Company has concluded that the most significant impact of the standard relates to the incremental disclosures required. In October 2016, the FASB issued ASU 2016-16, Income Tax - Intra-Entity Transfers of Assets Other than Inventory. The amendment improves the accounting for the income tax consequences of intra-entity transfers of assets other than inventory. The Company adopted the amendment on a modified retrospective basis effective January 1, 2018. As a result of adoption, the Company recorded a cumulative effect adjustment that reduced retained earnings by $1.6 million. In March 2017, the FASB issued ASU 2017-07, Compensation-Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost. The amendment requires an employer to report the service cost component of net benefit cost in the same line item as other compensation costs arising from services rendered by the pertinent employees during the period. The other components of net benefit cost are required to be presented in the income statement separately from the service cost component and outside a subtotal of income from operations. In addition, the amendment allows only the service cost component to be eligible for capitalization when applicable. The Company adopted the amendment in the first quarter of 2018. Adoption did not have a material impact on the Company's consolidated financial statements. Standards to be implemented The Company is evaluating the impact that the below standards to be implemented will have on the Company's consolidated financial statements. In February 2016, FASB issued ASU 2016-02, Leases (Topic 842). The amendment increases transparency and comparability among organizations by recognizing lease assets and lease liabilities on the balance sheet and disclosing key information about leasing arrangements. In February 2018, FASB issued ASU 2018-01, Leases (Topic 842): Land Easement Practical Expedient for Transition to Topic 842. The amendment clarifies that land easements are within the scope of the new leases standard (ASC 842) and introduces a new transition practical expedient allowing a company to not assess whether existing and expired land easements that were not previously accounted for as leases under current US GAAP (ASC 840) are or contain leases under ASC 842. The Company will adopt the new standard beginning on January 1, 2019. A modified retrospective transition approach is required for leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements, with certain practical expedients available. While the Company is still continuing to assess the effect of adoption, it expects that the new standard will have a material effect on its consolidated balance sheet related to the recognition of new assets and lease liabilities. In preparation for the adoption of the guidance, the Company is in the process of implementing new software to enable the preparation of financial information.

REVENUES

3 Months Ended

Mar. 31, 2018

Revenue from Contract with Customer [Abstract]

REVENUES

Revenue Recognition

Revenues are recognized 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.

Nature of Goods and Services

The Company generates services and product revenues through its Environmental Services and Safety-Kleen operating segments. The majority of the Company’s contracts 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 term between invoicing and when payment is due is not significant. The Company excludes sales taxes that it collects from customers from its revenues.

Disaggregation of Revenue

The following table presents our revenues disaggregated by revenue source (in thousands):



	Three Months Ended March 31, 2018
	Environmental Services		Safety-Kleen		Corporate		Total
Primary Geographical Markets
United States	$	343,972	$	287,642	$	145	$	631,759
Canada	95,716		22,276		27		118,019
	439,688		309,918		172		749,778
Sources of Revenue (1)
Technical Services	236,306		—		—		236,306
Field and Emergency Response Services	69,935		—		—		69,935
Industrial Services	103,763		—		—		103,763
Oil, Gas and Lodging Services and Other	29,684		—		172		29,856
Safety-Kleen Environmental Services	—		194,161		—		194,161
Kleen Performance Products	—		115,757		—		115,757
Total third party revenues	$	439,688	$	309,918	$	172	$	749,778



	Three Months Ended March 31, 2017
	Environmental Services		Safety-Kleen		Corporate		Total
Primary Geographical Markets
United States	$	313,783	$	272,071	$	133	$	585,987
Canada	82,124		20,830		—		102,954
	395,907		292,901		133		688,941
Sources of Revenue (1)
Technical Services	230,218		—		—		230,218
Field and Emergency Response Services	61,019		—		—		61,019
Industrial Services	75,068		—		—		75,068
Oil, Gas and Lodging Services and Other	29,602		—		133		29,735
Safety-Kleen Environmental Services	—		191,727		—		191,727
Kleen Performance Products	—		101,174		—		101,174
Total third party revenues	$	395,907	$	292,901	$	133	$	688,941

______________________


1.	All revenue except Kleen Performance Products and product sales within Safety-Kleen Environmental Services, including allied products and direct blended oil sales, are recognized over time. Kleen Performance Products and Safety-Kleen Environmental Services product revenues are recognized at a point in time.

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

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

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

Safety-Kleen Environmental Services. Safety-Kleen Environmental Services revenues are generated from providing parts washer services, containerized waste handling and disposal services, oil collection services, direct sales of blended oil products, and other complementary services and product sales. Containerized waste services consist of profiling, collecting, transporting and recycling or disposing of a wide variety of waste. Other complementary products and services include vacuum services, sale of allied supply products and other environmental services. Revenues from parts washer services include fees charged to customers for their use of parts washer equipment, to clean and maintain parts washer equipment and to remove and replace used cleaning fluids. Parts washer services are considered a single performance obligation due to the highly integrated and interdependent nature of the arrangement. Revenue from parts washer services is recognized over the service interval as the customer receives the benefit of the service. Collection and transportation revenues are recognized 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. Product revenue is recognized upon the transfer of control. Control transfers when the products are delivered to the customer.

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

Oil, Gas and Lodging Services and Other. Oil, Gas and Lodging Services and Other is primarily comprised of revenues generated from providing Oil and Gas Field Services that support upstream activities such as exploration and drilling for oil and gas companies and Lodging Services to customers in Western Canada. The Company recognizes Oil and Gas Field Services revenue over time, as the customer receives and consumes the benefits of the 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. Revenue for lodging accommodation services is recognized over time based on passage of time. Revenue for manufacturing services is recognized over time using a cost-to-cost measure of progress or completed units to depict the transfer of assets to the customer.

Contract Balances



	March 31, 2018		December 31, 2017		March 31, 2017		December 31, 2016
Receivables	$	551,841	$	528,924	$	480,044	$	496,226
Contract Assets	63,375		35,922		28,106		36,190
Contract Liabilities	68,748		67,822		64,379		64,397

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 receive 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. As part of the acquisition of the Veolia Business on February 23, 2018, the Company acquired receivables and contract assets of $22.1 million and $18.7 million, respectively. Changes in the contract asset and liability balances during the three-month period ended March 31, 2018 and March 31, 2017 were not materially impacted by any other factors. The contract liability balances at the beginning of each period presented were fully recognized in the subsequent three-month period.

Remaining Performance Obligations

Remaining performance obligations represent the transaction price of orders for which work has not been performed. As of March 31, 2018, all remaining performance obligations were for contracts with an original expected length of one year or less.

Variable Consideration

The nature of the Company's contracts gives rise to certain types of variable consideration, including in limited cases volume and payment discounts. The Company estimates the amount of variable consideration to include in the estimated transaction price based on historical experience, anticipated performance and its best judgment at the time and to the extent it is probable that a significant reversal of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is resolved. Variable consideration was not material in any of the periods presented.

Contract Costs

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

BUSINESS COMBINATIONS

3 Months Ended

Mar. 31, 2018

Business Combinations [Abstract]

BUSINESS COMBINATIONS

2018 Acquisition

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 will provide 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 $120.0 million subject to certain post-closing adjustments. The acquisition was financed with cash on hand. The amount of revenue from the Veolia Business included in the Company's results of operations for the period ended March 31, 2018 was $17.6 million. The amount of pre-tax income for the period ended March 31, 2018 was immaterial. During the three months ended March 31, 2018, the Company incurred acquisition-related costs of approximately $0.5 million in connection with the transaction which are included in selling, general and administrative expenses in the consolidated statements of operations.

The allocation of the purchase price was based on preliminary estimates of the fair value of assets acquired and liabilities assumed as of February 23, 2018, as the Company is continuing to obtain information to complete its valuation of these accounts and the associated tax accounting. The components and preliminary allocation of the purchase price consist of the following amounts (in thousands):



	At Acquisition Date
Accounts receivable, including unbilled receivables	$	40,773
Inventories and supplies	1,442
Prepaid expenses and other current assets	1,005
Property, plant and equipment	72,244
Permits and other intangibles	5,140
Current liabilities	(15,908		)
Closure and post-closure liabilities	(604		)
Total identifiable net assets	104,092
Goodwill	15,908
Total purchase price, net of cash acquired	$	120,000

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

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

2017 Acquisitions

On October 16, 2017, the Company acquired a division of a privately held company for $4.8 million. This acquisition provides the Company with additional fabrication and refurbishment capabilities for its fleet of trucks. The acquired division is included in the Environmental Services segment. In connection with this acquisition, there was minimal goodwill recognized.

On September 22, 2017, the Company acquired a privately held company which manufactures and sells parts washer machines and related equipment for $2.1 million. The acquired company is included in the Safety-Kleen operating segment. In connection with this acquisition, goodwill totaling $0.7 million was recognized.

On July 14, 2017, the Company acquired Lonestar West Inc. ("Lonestar"), a public company headquartered in Alberta, Canada, for approximately CAD $41.8 million, ($33.1 million USD), net of cash acquired, which included an equity payout of CAD $0.72 per share to Lonestar shareholders and the assumption of approximately CAD $21.3 million ($16.8 million USD) in outstanding debt, which Clean Harbors subsequently repaid. The acquisition is expected to support the Company's growth in the daylighting and hydro excavation services markets. In addition to increasing the size of the Company's hydro vac fleet, Lonestar's network of locations will provide the Company with direct access to key geographic markets in both the United States and Canada. The acquired company is included in the Environmental Services segment. The primary areas of the preliminary purchase price allocation that are subject to change relate to certain legal matters, income and income based taxes and residual goodwill. Measurement period adjustments are recorded in the reporting period in which the estimates are finalized and adjustment amounts are determined. In connection with this acquisition, a preliminary goodwill amount of $2.9 million was recognized.

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

Pro forma financial information on a comparative basis, as if these acquisitions had been completed on January 1, 2017, is not presented as the pro forma results would not be materially different from reported trends and operations.

DISPOSITION OF BUSINESS

3 Months Ended

Mar. 31, 2018

Discontinued Operations and Disposal Groups [Abstract]

DISPOSITION OF BUSINESS

On June 30, 2017, the Company completed the sale of its Transformer Services business, as part of its continuous focus on improving or divesting certain non-core operations. The sale price was $45.5 million. The Transformer Services business was a non-core business previously included within the legacy Technical Services operating segment.

The following table presents income attributable to the Transformer Services business included in the Company's consolidated results of operations for the three months ended March 31, 2017 (in thousands):



	Three Months Ended
	March 31, 2017
Income before provision for income taxes	$	898

INVENTORIES AND SUPPLIES

3 Months Ended

Mar. 31, 2018

Inventory Disclosure [Abstract]

INVENTORIES AND SUPPLIES

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



	March 31, 2018		December 31, 2017
Oil and oil products	$	59,243	$	58,142
Supplies and drums	97,246		94,242
Solvent and solutions	9,188		9,167
Modular camp accommodations	2,247		1,826
Other	13,514		12,635
Total inventories and supplies	$	181,438	$	176,012

As of March 31, 2018 and December 31, 2017, other inventories consisted primarily of parts washer components, cleaning fluids, absorbents and automotive fluids, such as windshield washer fluid and antifreeze. Supplies and drums consist primarily of drums and containers as well as critical spare parts to support the Company's incinerator and re-refinery operations.

PROPERTY, PLANT AND EQUIPMENT

3 Months Ended

Mar. 31, 2018

Property, Plant and Equipment [Abstract]

PROPERTY, PLANT AND EQUIPMENT

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



	March 31, 2018		December 31, 2017
Land	$	124,331	$	121,658
Asset retirement costs (non-landfill)	14,794		14,593
Landfill assets	145,177		144,539
Buildings and improvements	421,749		414,384
Camp equipment	165,104		170,012
Vehicles	676,749		617,959
Equipment	1,659,335		1,644,102
Furniture and fixtures	5,656		5,708
Construction in progress	47,034		57,618
	3,259,929		3,190,573
Less - accumulated depreciation and amortization	1,628,281		1,603,208
Total property, plant and equipment, net	$	1,631,648	$	1,587,365

Interest in the amount of $0.3 million and $0.1 million was capitalized to property, plant and equipment during the three months ended March 31, 2018 and March 31, 2017 respectively. Depreciation expense, inclusive of landfill amortization, was $65.6 million and $63.3 million for the three months ended March 31, 2018 and March 31, 2017, respectively.

GOODWILL AND OTHER INTANGIBLE ASSETS

3 Months Ended

Mar. 31, 2018

Goodwill and Intangible Assets Disclosure [Abstract]

GOODWILL AND OTHER INTANGIBLE ASSETS

The changes in goodwill by segment for the three months ended March 31, 2018 were as follows (in thousands):



	Environmental Services			Safety-Kleen			Totals
Balance at January 1, 2018	$	172,386		$	306,137		$	478,523
Increase from current period acquisition	15,908			—			15,908
Measurement period adjustments from prior period acquisitions	(9		)	—			(9		)
Foreign currency translation	(795		)	(922		)	(1,717		)
Balance at March 31, 2018	$	187,490		$	305,215		$	492,705

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

As discussed in Note 18, “Segment Reporting,” during the first quarter of fiscal year 2018 and as a result of operational and managerial changes in several of the Company’s businesses, the identification of operating segments in accordance with ASC 280, Segment Information, was changed. As a result of the Company's conclusions around the identification of operating segments, the Company also concluded that, for purposes of reviewing for potential goodwill impairment, it now has four reporting units, consisting of Environmental Sales and Service, Environmental Facilities, Kleen Performance Products and Safety-Kleen Environmental Services. The Company allocated goodwill to the newly identified reporting units using a relative fair value approach. In addition, the Company completed an assessment of any potential goodwill impairment for all reporting units immediately prior and subsequent to the reallocation and determined that no impairment existed.

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



	March 31, 2018						December 31, 2017
	Cost		Accumulated Amortization		Net		Cost		Accumulated Amortization		Net
Permits	$	174,867	$	75,493	$	99,374	$	174,721	$	74,347	$	100,374
Customer and supplier relationships	400,385		165,056		235,329		399,224		158,972		240,252
Other intangible assets	38,071		31,170		6,901		36,766		31,592		5,174
Total amortizable permits and other intangible assets	613,323		271,719		341,604		610,711		264,911		345,800
Indefinite lived trademarks and trade names	123,031		—		123,031		123,328		—		123,328
Total permits and other intangible assets	$	736,354	$	271,719	$	464,635	$	734,039	$	264,911	$	469,128

Amortization expense of permits and other intangible assets was $9.2 million and $9.1 million in the three months ended March 31, 2018 and March 31, 2017, respectively.

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



Years Ending December 31,	Expected Amortization
2018 (nine months)	$	26,018
2019	32,247
2020	29,486
2021	27,492
2022	27,342
Thereafter	199,019
	$	341,604

- Definition

The entire disclosure for the aggregate amount of goodwill and a description of intangible assets, which may include (a) for amortizable intangible assets (also referred to as finite-lived intangible assets), the carrying amount, the amount of any significant residual value, and the weighted-average amortization period, (b) for intangible assets not subject to amortization (also referred to as indefinite-lived intangible assets), the carrying amount, and (c) the amount of research and development assets acquired and written off in the period, including the line item in the income statement in which the amounts written off are aggregated, if not readily apparent from the income statement. Also discloses (a) for amortizable intangibles assets in total and by major class, the gross carrying amount and accumulated amortization, the total amortization expense for the period, and the estimated aggregate amortization expense for each of the five succeeding fiscal years, (b) for intangible assets not subject to amortization the carrying amount in total and by major class, and (c) for goodwill, in total and for each reportable segment, the changes in the carrying amount of goodwill during the period (including the aggregate amount of goodwill acquired, the aggregate amount of impairment losses recognized, and the amount of goodwill included in the gain (loss) on disposal of a reporting unit). If any part of goodwill has not been allocated to a reportable segment, discloses the unallocated amount and the reasons for not allocating. For each impairment loss recognized related to an intangible asset (excluding goodwill), discloses: (a) a description of the impaired intangible asset and the facts and circumstances leading to the impairment, (b) the amount of the impairment loss and the method for determining fair value, (c) the caption in the income statement or the statement of activities in which the impairment loss is aggregated, and (d) the segment in which the impaired intangible asset is reported. For each goodwill impairment loss recognized, discloses: (a) a description of the facts and circumstances leading to the impairment, (b) the amount of the impairment loss and the method of determining the fair value of the associated reporting unit, and (c) if a recognized impairment loss is an estimate not finalized and the reasons why the estimate is not final. May also disclose the nature and amount of any significant adjustments made to a previous estimate of an impairment loss.

+ References + Details

CLOSURE AND POST-CLOSURE LIABILITIES

3 Months Ended

Mar. 31, 2018

Asset Retirement Obligation Disclosure [Abstract]

CLOSURE AND POST-CLOSURE LIABILITIES

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



	Landfill Retirement Liability			Non-Landfill Retirement Liability			Total
Balance at January 1, 2018	$	32,382		$	28,655		$	61,037
Liabilities assumed in acquisition	—			604			604
New asset retirement obligations	1,053			—			1,053
Accretion	646			619			1,265
Changes in estimates recorded to statement of operations	—			30			30
Changes in estimates recorded to balance sheet	441			—			441
Expenditures	(155		)	(62		)	(217		)
Currency translation and other	(78		)	(55		)	(133		)
Balance at March 31, 2018	$	34,289		$	29,791		$	64,080

All of the landfill facilities included in the above were active as of March 31, 2018. There were no significant charges (benefits) in 2018 resulting from changes in estimates for closure and post-closure liabilities.

New asset retirement obligations incurred during the first three months of 2018 were discounted at the credit-adjusted risk-free rate of 5.66%.

REMEDIAL LIABILITIES

3 Months Ended

Mar. 31, 2018

Environmental Remediation Obligations [Abstract]

REMEDIAL LIABILITIES

The changes to remedial liabilities for the three months ended March 31, 2018 were as follows (in thousands):



	Remedial Liabilities for Landfill Sites			Remedial Liabilities for Inactive Sites			Remedial Liabilities (Including Superfund) for Non-Landfill Operations			Total
Balance at January 1, 2018	$	1,800		$	65,342		$	57,326		$	124,468
Accretion	21			672			472			1,165
Changes in estimates recorded to statement of operations	—			(24		)	(568		)	(592		)
Expenditures	(12		)	(826		)	(1,370		)	(2,208		)
Currency translation and other	—			(9		)	(377		)	(386		)
Balance at March 31, 2018	$	1,809		$	65,155		$	55,483		$	122,447

In the three months ended March 31, 2018, there were no significant charges (benefits) resulting from changes in estimates for remedial liabilities.

FINANCING ARRANGEMENTS

3 Months Ended

Mar. 31, 2018

Debt Disclosure [Abstract]

FINANCING ARRANGEMENTS

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



	March 31, 2018			December 31, 2017
Senior secured Term Loan Agreement ("Term Loan Agreement")	$	4,000		$	4,000
Current portion of long-term obligations, at carrying value	$	4,000		$	4,000

Senior secured Term Loan Agreement due June 30, 2024	$	393,000		$	394,000
Senior unsecured notes, at 5.25%, due August 1, 2020 ("2020 Notes")	400,000			400,000
Senior unsecured notes, at 5.125%, due June 1, 2021 ("2021 Notes")	845,000			845,000
Long-term obligations, at par	$	1,638,000		$	1,639,000
Unamortized debt issuance costs and premium, net	(12,741		)	(13,463		)
Long-term obligations, at carrying value	$	1,625,259		$	1,625,537

Total current and long-term obligations, at carrying value	$	1,629,259		$	1,629,537

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

At March 31, 2018 and December 31, 2017, the fair value of the Term Loans was $398.2 million and $400.5 million, respectively, based on quoted market prices or other available market data. At March 31, 2018 and December 31, 2017, the fair value of the Company's 2020 Notes was $401.6 million and $404.6 million, respectively, based on quoted market prices for the instrument. At March 31, 2018 and December 31, 2017, the fair value of the Company's 2021 Notes was $855.3 million and $855.7 million, respectively, based on quoted market prices for the instrument. The fair values of the Term Loans, 2020 Notes and 2021 Notes are considered Level 2 measures according to the fair value hierarchy.

The Company also maintains a $400.0 million revolving credit facility under which the Company had no outstanding loan balances as of March 31, 2018 and December 31, 2017. At March 31, 2018, approximately $237.0 million was available to borrow and outstanding letters of credit were $132.9 million. At December 31, 2017, $217.8 million was available to borrow and outstanding letters of credit were $134.1 million.

LOSS PER SHARE

3 Months Ended

Mar. 31, 2018

Earnings Per Share [Abstract]

LOSS PER SHARE

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



	Three Months Ended
	March 31,
	2018			2017
Numerator for basic and diluted loss per share:
Net loss	$	(12,631	)	$	(21,393	)

Denominator:
Basic shares outstanding	56,457			57,262
Dilutive effect of equity-based compensation awards	—			—
Dilutive shares outstanding	56,457			57,262

Basic loss per share:	$	(0.22	)	$	(0.37	)

Diluted loss per share:	$	(0.22	)	$	(0.37	)

As a result of the net loss reported for the three months ended March 31, 2018 and March 31, 2017, all then outstanding restricted stock awards and performance awards totaling 896,180 and 659,558, respectively, were excluded from the calculation of diluted loss per share as their inclusion would have an antidilutive effect.

ACCUMULATED OTHER COMPREHENSIVE LOSS

3 Months Ended

Mar. 31, 2018

Equity [Abstract]

ACCUMULATED OTHER COMPREHENSIVE LOSS

The changes in accumulated other comprehensive loss by component and related tax effects for the three months ended March 31, 2018 were as follows (in thousands):



	Foreign Currency Translation			Unrealized Losses on Available-For-Sale Securities			Unfunded Pension Liability			Total
Balance at January 1, 2018	$	(170,575	)	$	(146	)	$	(1,686	)	$	(172,407	)
Other comprehensive loss before tax effects	(16,551		)	(115		)	—			(16,666		)
Tax effects	—			(80		)	—			(80		)
Other comprehensive loss	$	(16,551	)	$	(195	)	$	—		$	(16,746	)
Balance at March 31, 2018	$	(187,126	)	$	(341	)	$	(1,686	)	$	(189,153	)

STOCK-BASED COMPENSATION

3 Months Ended

Mar. 31, 2018

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

STOCK-BASED COMPENSATION

Total stock-based compensation cost charged to selling, general and administrative expenses for the three months ended March 31, 2018 and March 31, 2017 was $3.1 million and $2.3 million, respectively. The total income tax benefit recognized in the consolidated statements of operations from stock-based compensation was $0.9 million and $0.8 million for the three months ended March 31, 2018 and March 31, 2017, respectively.

Restricted Stock Awards

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

The following table summarizes information about restricted stock awards for the three months ended March 31, 2018:



Restricted Stock	Number of Shares		Weighted Average Grant-Date Fair Value
Balance at January 1, 2018	604,933		$	54.23
Granted	149,200		$	53.43
Vested	(25,558	)	$	52.65
Forfeited	(6,772	)	$	52.65
Balance at March 31, 2018	721,803		$	54.13

As of March 31, 2018, there was $28.5 million of total unrecognized compensation cost arising from restricted stock awards under the Company's Plans. 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 the three months ended March 31, 2018 and March 31, 2017 was $1.3 million and $1.5 million, respectively.

Performance Stock Awards

The following information relates to performance stock awards that have been granted to employees under the Company's Plans. Performance stock awards are subject to performance criteria established by the compensation committee of the Company's board of directors prior to or at the date of grant. The vesting of the performance stock awards is based on achieving such targets typically based on revenue, Adjusted EBITDA margin, Adjusted Free Cash Flow and Total Recordable Incident Rate. In addition, performance stock awards include continued service conditions. The fair value of each performance stock award is based on the closing price of the Company's common stock on the date of grant and is amortized to expense over the service period if achievement of performance measures is considered probable.

The following table summarizes information about performance stock awards for the three months ended March 31, 2018:



Performance Stock	Number of Shares		Weighted Average Grant-Date Fair Value
Balance at January 1, 2018	190,129		$	55.63
Granted	—		$	—
Vested	(8,696	)	$	54.26
Forfeited	(7,056	)	$	54.64
Balance at March 31, 2018	174,377		$	55.74

As of March 31, 2018, there was $2.0 million of total unrecognized compensation cost arising from unvested performance stock awards deemed probable of vesting under the Company's Plans. The total fair value of performance awards vested during the three months ended March 31, 2018 and March 31, 2017 was $0.5 million and $1.4 million, respectively.

Common Stock Repurchases

On October 31, 2017, the Company's board of directors increased the size of the Company’s current share repurchase program from $300 million to $600 million. During the three months ended March 31, 2018 and March 31, 2017, the Company repurchased and retired a total of 0.3 million shares and 0.1 million shares, respectively, of the Company's common stock for a total cost of $14.3 million and $6.8 million, respectively. Through March 31, 2018, the Company has repurchased and retired a total of 5.1 million shares of the Company's common stock for a total cost of $263.1 million under this program. As of March 31, 2018, an additional $336.9 million remained available for repurchase of shares under the current authorized program.

COMMITMENTS AND CONTINGENCIES	3 Months Ended
COMMITMENTS AND CONTINGENCIES	Mar. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES Legal and Administrative Proceedings The Company and its subsidiaries are subject to legal proceedings and claims arising in the ordinary course of business. Actions filed against the Company arise from commercial and employment-related claims including alleged class actions related to sales practices and wage and hour claims. The plaintiffs in these actions may be seeking damages or injunctive relief or both. These actions are in various jurisdictions and stages of proceedings, and some are covered in part by insurance. In addition, the Company’s waste management services operations are regulated by federal, state, provincial and local laws enacted to regulate discharge of materials into the environment, remediation of contaminated soil and groundwater or otherwise protect the environment. This ongoing regulation results in the Company frequently becoming a party to legal or administrative proceedings involving all levels of governmental authorities and other interested parties. The issues involved in such proceedings generally relate to alleged violations of existing permits and licenses or alleged responsibility under federal or state Superfund laws to remediate contamination at properties owned either by the Company or by other parties (“third party sites”) to which either the Company or the prior owners of certain of the Company’s facilities shipped wastes. At March 31, 2018 and December 31, 2017, the Company had recorded reserves of $19.9 million and $19.3 million, respectively, in the Company's financial statements for actual or probable liabilities related to the legal and administrative proceedings in which the Company was then involved, the principal of which are described below. At March 31, 2018 and December 31, 2017, the Company also believed that it was reasonably possible that the amount of these potential liabilities could be as much as $1.7 million and $1.8 million more, respectively. 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 March 31, 2018 and December 31, 2017, the $19.9 million and $19.3 million, respectively, of reserves consisted of (i) $17.8 million and $17.9 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) $2.1 million and $1.4 million, respectively, primarily related to federal, state and provincial enforcement actions, which were included in accrued expenses on the consolidated balance sheets. As of March 31, 2018, the principal legal and administrative proceedings in which the Company was involved, or which had been terminated during 2018, were as follows: Ville Mercier. In September 2002, the Company acquired the stock of a subsidiary (the "Mercier Subsidiary") which owns a hazardous waste incinerator in Ville Mercier, Quebec (the "Mercier Facility"). The property adjacent to the Mercier Facility, which is also owned by the Mercier Subsidiary, is now contaminated as a result of actions dating back to 1968, when the Government of Quebec issued to a company unrelated to the Mercier Subsidiary two permits to dump organic liquids into lagoons on the property. In 1999, Ville Mercier and three neighboring municipalities filed separate legal proceedings against the Mercier Subsidiary and the Government of Quebec. In 2012, the municipalities amended their existing statement of claim to seek $2.9 million (CAD) in general damages and $10.0 million (CAD) in punitive damages, plus interest and costs, as well as injunctive relief. Both the Government of Quebec and the Company have filed summary judgment motions against the municipalities. The parties are currently 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 March 31, 2018 were as follows: Product Liability Cases. Safety-Kleen has been named as a defendant in various lawsuits that are currently pending in various courts and jurisdictions throughout the United States, including approximately 59 proceedings (excluding cases which have been settled but not formally dismissed) as of March 31, 2018, wherein persons claim personal injury resulting from the use of Safety-Kleen's parts cleaning equipment or cleaning products. These proceedings typically involve allegations that the solvent used in Safety-Kleen's parts cleaning equipment contains contaminants and/or that Safety-Kleen's recycling process does not effectively remove the contaminants that become entrained in the solvent during their use. In addition, certain claimants assert that Safety-Kleen failed to warn adequately the product user of potential risks, including a historic failure to warn that solvent contains trace amounts of toxic or hazardous substances such as benzene. Safety-Kleen maintains insurance that it believes will provide coverage for these product liability claims (over amounts accrued for self-insured retentions and deductibles in certain limited cases), except for punitive damages to the extent not insurable under state law or excluded from insurance coverage. Safety-Kleen also believes that these claims lack merit and has historically vigorously defended, and intends to continue to vigorously defend, itself and the safety of its products against all of these claims. Such matters are subject to many uncertainties and outcomes are not predictable with assurance. Consequently, Safety-Kleen is unable to ascertain the ultimate aggregate amount of monetary liability or financial impact with respect to these matters as of March 31, 2018. From January 1, 2018 to March 31, 2018, three product liability claims were settled or dismissed. Due to the nature of these claims and the related insurance, the Company did not incur any expense as Safety-Kleen's insurance provided coverage in full for all such claims. Safety-Kleen may be named in similar, additional lawsuits in the future, including claims for which insurance coverage may not be available. Superfund Proceedings The Company has been notified that either the Company (which, since December 28, 2012, includes Safety-Kleen) or the prior owners of certain of the Company's facilities for which the Company may have certain indemnification obligations have been identified as potentially responsible parties ("PRPs") or potential PRPs in connection with 127 sites which are subject to or are proposed to become subject to proceedings under federal or state Superfund laws. Of the 127 sites, three (including the BR Facility described below) involve facilities that are now owned or leased by the Company and 124 involve third party sites to which either the Company or the prior owners of certain of the Company’s facilities shipped wastes. Of the 124 third party sites, 33 are now settled, 16 are currently requiring expenditures on remediation and 75 are not currently requiring expenditures on remediation. In connection with each site, the Company has estimated the extent, if any, to which it may be subject, either directly or as a result of any indemnification obligations, for cleanup and remediation costs, related legal and consulting costs associated with PRP investigations, settlements, and related legal and administrative proceedings. The amount of such actual and potential liability is inherently difficult to estimate because of, among other relevant factors, uncertainties as to the legal liability (if any) of the Company or the prior owners of certain of the Company's facilities to contribute a portion of the cleanup costs, the assumptions that must be made in calculating the estimated cost and timing of remediation, the identification of other PRPs and their respective capability and obligation to contribute to remediation efforts, and the existence and legal standing of indemnification agreements (if any) with prior owners, which may either benefit the Company or subject the Company to potential indemnification obligations. The Company believes its potential liability could exceed $100,000 at 11 of the 124 third party 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 Environmental Protection Agency (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. The Company is currently performing corrective actions at the BR Facility under an order issued by the Louisiana Department of Environmental Quality, and has begun conducting the remedial investigation and feasibility study under an order issued by the EPA. The Company cannot presently estimate the potential additional liability for the Devil's Swamp cleanup until a final remedy is selected by the EPA. Third Party Sites. Of the 124 third party sites at which the Company has been notified it is a PRP or potential PRP or may have indemnification obligations, Clean Harbors has an indemnification agreement at 11 of these sites with ChemWaste, a former subsidiary of Waste Management, Inc., and at six additional of these third party sites, Safety-Kleen has a similar indemnification agreement with McKesson Corporation. These agreements indemnify the Company (which now includes Safety-Kleen) with respect to any liability at the 17 sites for waste disposed prior to the Company's (or Safety-Kleen's) acquisition of the former subsidiaries of Waste Management and McKesson which had shipped wastes to those sites. Accordingly, Waste Management or McKesson are paying all costs of defending those subsidiaries in those 17 cases, including legal fees and settlement costs. However, there can be no guarantee that the Company's ultimate liabilities for those sites will not exceed the amount recorded or that indemnities applicable to any of these sites will be available to pay all or a portion of related costs. Except for the indemnification agreements which the Company holds from ChemWaste, McKesson and one other entity, the Company does not have an indemnity agreement with respect to any of the 124 third party sites discussed above. Federal and State 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 March 31, 2018 and December 31, 2017, there were five proceedings for which the Company reasonably believes that the sanctions could equal or exceed $100,000. The Company believes that the fines or other penalties in these or any of the other regulatory proceedings will, individually or in the aggregate, not have a material effect on its financial condition, results of operations or cash flows.

INCOME TAXES	3 Months Ended
INCOME TAXES	Mar. 31, 2018
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES The Company records a tax provision or benefit on an interim basis using an estimated annual effective tax rate. This rate is applied to the current period ordinary income or loss to determine the income tax provision or benefit allocated to the interim period. Losses from jurisdictions for which no benefit can be recognized and the income tax effects of unusual or infrequent items are excluded from the estimated annual effective tax rate and are recognized in the impacted interim period. The estimated annual effective tax rate may be significantly impacted by projected earnings mix by tax jurisdiction. Adjustments to the estimated annual effective income tax rate are recognized in the period when such estimates are revised. The Company’s effective tax rate for the three months ended March 31, 2018 was (31.9)% compared to (14.5)% for the same period in 2017. The variations in the effective income tax rates for the three months ended March 31, 2018 as compared to more customary relationships between pre-tax income and the provision for income taxes were primarily due to the Company not recognizing income tax benefits from current operating losses related to certain Canadian entities in those periods. On December 22, 2017, the “Tax Cuts and Jobs Act” (the “Tax Act”) was signed into law, making significant changes to the federal tax law. Changes include, but are not limited to, a corporate tax rate decrease from 35% to 21% effective for tax years beginning after December 31, 2017, the transition of U.S. international taxation from a worldwide tax system to a territorial tax system, and a one-time transition tax on the mandatory deemed repatriation of cumulative foreign earnings as of December 31, 2017. The Company recognized its best estimate of the income tax effects of the 2017 Tax Act in the financial statements included in its 2017 Annual Report on Form 10-K in accordance with Staff Accounting Bulletin No. 118, which provides SEC staff guidance for the application of ASC Topic 740, Income Taxes, in the reporting period in which the 2017 Tax Act was signed into law. During the three months ended March 31, 2018, the Company did not recognize any changes to the provisional amounts recorded in its 2017 Annual Report on Form 10-K in connection with the 2017 Tax Act. The Company is continuing to evaluate the impact of the Tax Act on its business and the consolidated financial statements and will make any adjustments to its provisional amounts in subsequent reporting periods upon obtaining, preparing or analyzing additional information affecting the income tax effects initially reported as a provisional amount. Any subsequent adjustment to these amounts will be recorded to tax expense in the quarter of 2018 when the analysis is complete. As of March 31, 2018 and December 31, 2017, the Company had recorded $5.6 million and $5.1 million, respectively, of liabilities for unrecognized tax benefits and $0.4 million and $0.5 million of interest, respectively. Due to expiring statute of limitation periods, the Company believes that total unrecognized tax benefits will decrease by $1.4 million within the next 12 months.

SEGMENT REPORTING

3 Months Ended

Mar. 31, 2018

Segment Reporting [Abstract]

SEGMENT REPORTING

Segment reporting is prepared on the same basis that the Company's chief executive officer, who is the Company's chief operating decision maker, manages the business, makes operating decisions and assesses performance. During the first quarter of fiscal year 2018, certain of the Company's businesses undertook a reorganization which included changes to the underlying business and management structures. The reorganization resulted in combining the Environmental Services businesses from an operational and management perspective and is expected to deepen customer relationships and allow for efficiencies across the Company's operations through the sharing of resources, namely labor and equipment which will reduce third party spend and promote the cross selling of such business offerings. In connection with this reorganization, the Company’s chief operating decision maker also requested changes in the information that he regularly reviews for purposes of allocating resources and assessing performance. These changes required a reconsideration of the Company’s operating segments in the first quarter of 2018 and resulted in a change in the Company’s assessment of its operating segments. Upon reconsideration of the identification of the Company’s operating segments, the Company concluded that there are now two operating segments for disclosure in accordance with ASC 280 Segment reporting; (i) the Environmental Services segment which consists of the Company’s historical Technical Services, Industrial Services, Field Services and Oil, Gas and Lodging businesses and (ii) the Safety-Kleen segment.

Third-party revenue is revenue billed to outside customers by a particular segment. Direct revenue is revenue allocated to the segment providing the product or service. Intersegment revenues represent the sharing of third-party revenues among the segments based on products and services provided by each segment as if the products and services were sold directly to the third-party. The intersegment revenues are shown net. The negative intersegment revenues are due to more transfers out of customer revenues to other segments than transfers in of customer revenues from other segments. The operations not managed through the Company’s operating segments described above are recorded as “Corporate Items.” Corporate Items revenues consist of two different operations for which the revenues are insignificant. Corporate Items cost of revenues represents certain central services that are not allocated to the Company's operating segments for internal reporting purposes. Corporate Items selling, general and administrative expenses include typical corporate items such as legal, accounting and other items of a general corporate nature that are not allocated to the Company’s operating segments.

The following table reconciles third party revenues to direct revenues for the three months ended March 31, 2018 and 2017 (in thousands):



	For the Three Months Ended March 31, 2018											For the Three Months Ended March 31, 2017
	Third party revenues		Intersegment revenues, net			Corporate Items, net			Direct revenues			Third party revenues		Intersegment revenues, net			Corporate Items, net			Direct revenues
Environmental Services	$	439,688	$	31,965		$	794		$	472,447		$	395,907	$	32,069		$	920		$	428,896
Safety-Kleen	309,918		(31,965		)	11			277,964			292,901		(32,069		)	3			260,835
Corporate Items	172		—			(805		)	(633		)	133		—			(923		)	(790		)
Total	$	749,778	$	—		$	—		$	749,778		$	688,941	$	—		$	—		$	688,941

The primary financial measure by which the Company evaluates the performance of its segments is "Adjusted EBITDA" which consists of net loss plus accretion of environmental liabilities, depreciation and amortization, interest expense, net, provision for income taxes and excludes other expense, 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 Three Months Ended
	March 31,
	2018			2017
Adjusted EBITDA:
Environmental Services	$	61,417		$	60,190
Safety-Kleen	61,884			52,368
Corporate Items	(35,036		)	(32,423		)
Total	$	88,265		$	80,135
Reconciliation to Consolidated Statements of Operations:
Accretion of environmental liabilities	2,430			2,290
Depreciation and amortization	74,844			72,412
Income from operations	10,991			5,433
Other expense, net	299			1,549
Interest expense, net of interest income	20,270			22,576
Loss before provision for income taxes	$	(9,578	)	$	(18,692	)

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



	March 31, 2018
	Environmental Services		Safety-Kleen		Corporate Items		Totals
Property, plant and equipment, net	$	998,340	$	553,308	$	80,000	$	1,631,648
Goodwill	187,490		305,215		—		492,705
Permits and other intangibles, net	99,401		365,234		—		464,635
Total assets	$	1,685,168	$	1,437,026	$	562,622	$	3,684,816



	December 31, 2017
	Environmental Services		Safety-Kleen		Corporate Items		Totals
Property, plant and equipment, net	$	927,139	$	582,162	$	78,064	$	1,587,365
Goodwill	172,386		306,137		—		478,523
Permits and other intangibles, net	97,519		371,609		—		469,128
Total assets	$	1,541,241	$	1,471,291	$	694,038	$	3,706,570

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



	March 31, 2018		December 31, 2017
United States	$	3,002,779	$	2,985,394
Canada	681,901		721,176
Other foreign	136		—
Total	$	3,684,816	$	3,706,570

GUARANTOR AND NON-GUARANTOR SUBSIDIARIES FINANCIAL INFORMATION

3 Months Ended

Mar. 31, 2018

Guarantor and Non-Guarantor Subsidiaries Financial Information [Abstract]

GUARANTOR AND NON-GUARANTOR SUBSIDIARIES FINANCIAL INFORMATION

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

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



	Clean Harbors, Inc.		Guarantor Subsidiaries		Non-Guarantor Subsidiaries		Consolidating Adjustments			Total
Assets:
Cash and cash equivalents	$	51,781	$	99,662	$	34,909	$	—		$	186,352
Short-term marketable securities	—		—		37,792		—			37,792
Intercompany receivables	244,228		600,975		63,875		(909,078		)	—
Accounts receivable, net	—		457,231		94,610		—			551,841
Other current assets	—		265,477		52,050		(13,690		)	303,837
Property, plant and equipment, net	—		1,249,417		382,231		—			1,631,648
Investments in subsidiaries	3,095,335		535,503		—		(3,630,838		)	—
Intercompany debt receivable	—		89,947		21,000		(110,947		)	—
Goodwill	—		431,574		61,131		—			492,705
Permits and other intangibles, net	—		407,887		56,748		—			464,635
Other long-term assets	1,938		12,385		1,695		(12		)	16,006
Total assets	$	3,393,282	$	4,150,058	$	806,041	$	(4,664,565	)	$	3,684,816
Liabilities and Stockholders’ Equity:
Current liabilities	$	22,210	$	382,937	$	133,227	$	(13,690	)	$	524,684
Intercompany payables	600,287		306,401		2,390		(909,078		)	—
Closure, post-closure and remedial liabilities, net	—		149,316		17,388		—			166,704
Long-term obligations, net	1,625,259		—		—		—			1,625,259
Intercompany debt payable	—		21,000		89,947		(110,947		)	—
Other long-term liabilities	—		201,053		21,602		(12		)	222,643
Total liabilities	2,247,756		1,060,707		264,554		(1,033,727		)	2,539,290
Stockholders’ equity	1,145,526		3,089,351		541,487		(3,630,838		)	1,145,526
Total liabilities and stockholders’ equity	$	3,393,282	$	4,150,058	$	806,041	$	(4,664,565	)	$	3,684,816

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



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

Following is the consolidating statement of operations for the three months ended March 31, 2018 (in thousands):



	Clean Harbors, Inc.			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating Adjustments			Total
Revenues
Service revenues	$	—		$	481,483		$	152,401		$	(14,165	)	$	619,719
Product revenues	—			121,582			11,450			(2,973		)	130,059
Total revenues	—			603,065			163,851			(17,138		)	749,778
Cost of revenues (exclusive of items shown separately below)
Service cost of revenues	—			328,180			133,634			(14,165		)	447,649
Product cost of revenues	—			95,038			6,711			(2,973		)	98,776
Total cost of revenues	—			423,218			140,345			(17,138		)	546,425
Selling, general and administrative expenses	35			93,843			21,210			—			115,088
Accretion of environmental liabilities	—			2,176			254			—			2,430
Depreciation and amortization	—			53,704			21,140			—			74,844
(Loss) income from operations	(35		)	30,124			(19,098		)	—			10,991
Other expense, net	—			(85		)	(214		)	—			(299		)
Interest (expense) income, net	(20,999		)	505			224			—			(20,270		)
Equity in earnings of subsidiaries, net of taxes	2,514			(20,062		)	—			17,548			—
Intercompany interest income (expense)	—			1,361			(1,361		)	—			—
(Loss) income before (benefit) provision for income taxes	(18,520		)	11,843			(20,449		)	17,548			(9,578		)
(Benefit) provision for income taxes	(5,889		)	9,101			(159		)	—			3,053
Net (loss) income	(12,631		)	2,742			(20,290		)	17,548			(12,631		)
Other comprehensive loss	(16,746		)	(16,746		)	(14,007		)	30,753			(16,746		)
Comprehensive loss	$	(29,377	)	$	(14,004	)	$	(34,297	)	$	48,301		$	(29,377	)

Following is the consolidating statement of operations for the three months ended March 31, 2017 (in thousands):



	Clean Harbors, Inc.			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating Adjustments			Total
Revenues
Service revenues	$	—		$	443,305		$	131,071		$	(14,162	)	$	560,214
Product revenues	—			116,650			15,331			(3,254		)	128,727
Total revenues	—			559,955			146,402			(17,416		)	688,941
Cost of revenues (exclusive of items shown separately below)
Service cost of revenues	—			294,145			111,104			(14,162		)	391,087
Product cost of revenues	—			96,505			12,247			(3,254		)	105,498
Total cost of revenues	—			390,650			123,351			(17,416		)	496,585
Selling, general and administrative expenses	24			92,171			20,026			—			112,221
Accretion of environmental liabilities	—			2,055			235			—			2,290
Depreciation and amortization	—			51,900			20,512			—			72,412
(Loss) income from operations	(24		)	23,179			(17,722		)	—			5,433
Other expense, net	(146		)	(1,389		)	(14		)	—			(1,549		)
Interest (expense) income, net	(22,659		)	119			(36		)	—			(22,576		)
Equity in earnings of subsidiaries, net of taxes	(7,637		)	(21,824		)	—			29,461			—
Intercompany interest income (expense)	—			1,297			(1,297		)	—			—
(Loss) income before (benefit) provision for income taxes	(30,466		)	1,382			(19,069		)	29,461			(18,692		)
(Benefit) provision for income taxes	(9,073		)	9,637			2,137			—			2,701
Net loss	(21,393		)	(8,255		)	(21,206		)	29,461			(21,393		)
Other comprehensive income	6,051			6,051			5,032			(11,083		)	6,051
Comprehensive loss	$	(15,342	)	$	(2,204	)	$	(16,174	)	$	18,378		$	(15,342	)

Following is the condensed consolidating statement of cash flows for the three months ended March 31, 2018 (in thousands):



	Clean Harbors, Inc.			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating Adjustments			Total
Net cash from (used in) operating activities	$	143		$	69,536		$	(17,776	)	$	—		$	51,903
Cash flows used in investing activities:
Additions to property, plant and equipment	—			(37,319		)	(6,923		)	—			(44,242		)
Proceeds from sale and disposal of fixed assets	—			292			506			—			798
Acquisitions, net of cash acquired	—			(120,000		)	—			—			(120,000		)
Additions to intangible assets, including costs to obtain or renew permits	—			(1,234		)	(11		)	—			(1,245		)
Proceeds from sale of available-for-sale securities	—			—			3,264			—			3,264
Purchases of available-for-sale securities	—			—			(3,003		)	—			(3,003		)
Intercompany	—			(15,812		)	—			15,812			—
Net cash used in investing activities	—			(174,073		)	(6,167		)	15,812			(164,428		)

Cash flows used in financing activities:
Change in uncashed checks	—			(3,578		)	(265		)	—			(3,843		)
Tax payments related to withholdings on vested restricted stock	(548		)	—			—			—			(548		)
Repurchases of common stock	(14,264		)	—			—			—			(14,264		)
Principal payment on debt	(1,000		)	—			—			—			(1,000		)
Intercompany	15,812			—			—			(15,812		)	—
Net cash used in financing activities	—			(3,578		)	(265		)	(15,812		)	(19,655		)
Effect of exchange rate change on cash	—			—			(867		)	—			(867		)
Increase (decrease) in cash and cash equivalents	143			(108,115		)	(25,075		)	—			(133,047		)
Cash and cash equivalents, beginning of period	51,638			207,777			59,984			—			319,399
Cash and cash equivalents, end of period	$	51,781		$	99,662		$	34,909		$	—		$	186,352

Following is the condensed consolidating statement of cash flows for the three months ended March 31, 2017 (in thousands):



	Clean Harbors, Inc.			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating Adjustments			Total
Net cash (used in) from operating activities	$	(1,663	)	$	41,144		$	17,638		$	—		$	57,119
Cash flows from (used in) investing activities:
Additions to property, plant and equipment	—			(33,136		)	(9,326		)	—			(42,462		)
Proceeds from sale and disposal of fixed assets	—			664			366			—			1,030
Acquisitions, net of cash acquired	—			(11,946		)	—			—			(11,946		)
Proceeds from sale of business	1,837			—			181			—			2,018
Additions to intangible assets, including costs to obtain or renew permits	—			(573		)	(178		)	—			(751		)
Proceeds from sale of investments	243			—			—			—			243
Intercompany	—			(7,771		)	—			7,771			—
Net cash from (used in) investing activities	2,080			(52,762		)	(8,957		)	7,771			(51,868		)

Cash flows used in financing activities:
Change in uncashed checks	—			(5,165		)	(2,392		)	—			(7,557		)
Proceeds from exercise of stock options	46			—			—			—			46
Tax payments related to withholdings on vested restricted stock	(1,021		)	—			—			—			(1,021		)
Repurchases of common stock	(6,796		)	—			—			—			(6,796		)
Deferred financing costs paid	(108		)	—			—			—			(108		)
Intercompany	7,771			—			—			(7,771		)	—
Net cash used in financing activities	(108		)	(5,165		)	(2,392		)	(7,771		)	(15,436		)
Effect of exchange rate change on cash	—			—			554			—			554
Increase (decrease) in cash and cash equivalents	309			(16,783		)	6,843			—			(9,631		)
Cash and cash equivalents, beginning of period	51,417			155,943			99,637			—			306,997
Cash and cash equivalents, end of period	$	51,726		$	139,160		$	106,480		$	—		$	297,366

SIGNIFICANT ACCOUNTING POLICIES (Policies)	3 Months Ended
SIGNIFICANT ACCOUNTING POLICIES (Policies)	Mar. 31, 2018
Accounting Policies [Abstract]
Reclassifications	Reclassifications During the first quarter of fiscal year 2018, certain of the Company's businesses undertook a reorganization which included changes to the underlying business and management structures. The reorganization resulted in combining the Environmental Services businesses from an operational and management perspective and is expected to deepen customer relationships and allow for efficiencies across the Company's operations through the sharing of resources, namely labor and equipment which will reduce third party spend and promote the cross selling of such business offerings. In connection with this reorganization, the Company’s chief operating decision maker also requested changes in the information that he regularly reviews for purposes of allocating resources and assessing performance. These changes required a reconsideration of the Company’s operating segments in the first quarter of 2018 and resulted in a change in the Company’s assessment of its operating segments. Upon reconsideration of the identification of the Company’s operating segments, the Company concluded that there are now two operating segments for disclosure in accordance with ASC 280 Segment reporting; (i) the Environmental Services segment which consists of the Company’s historical Technical Services, Industrial Services, Field Services and Oil, Gas and Lodging businesses and (ii) the Safety-Kleen segment. See Note 18, "Segment Reporting," for more information. The amounts presented for the three months ended March 31, 2017 have been recast to reflect the impact of such changes. These reclassifications and adjustments had no effect on consolidated statements of operations, consolidated statements of comprehensive loss, consolidated statements of cash flows or consolidated statements of stockholders' equity for any of the periods presented.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Standards implemented In May 2014, the Financial Accounting Standards Board ("FASB") issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606), which replaces numerous requirements in U.S. GAAP, including industry-specific requirements, and provides companies with a single revenue recognition model for recognizing revenue from contracts with customers. The guidance permits two methods of adoption: retrospectively to each prior reporting period presented (full retrospective method), or retrospectively with the cumulative effect of initially applying the guidance recognized at the date of initial application (the modified retrospective method). On January 1, 2018, the Company adopted Topic 606 using the modified retrospective method for all contracts. Results for reporting periods beginning on the date of adoption are presented under ASC 606, while prior period amounts have not been adjusted and continue to be reported in accordance with the Company's historical accounting methodology pursuant to ASC 605, Revenue Recognition (“ASC 605”). Upon adoption, a cumulative effect adjustment was not required as the majority of the Company’s contracts are recognized based on time and materials incurred and were not impacted by the new guidance. The Company has concluded that the most significant impact of the standard relates to the incremental disclosures required. In October 2016, the FASB issued ASU 2016-16, Income Tax - Intra-Entity Transfers of Assets Other than Inventory. The amendment improves the accounting for the income tax consequences of intra-entity transfers of assets other than inventory. The Company adopted the amendment on a modified retrospective basis effective January 1, 2018. As a result of adoption, the Company recorded a cumulative effect adjustment that reduced retained earnings by $1.6 million. In March 2017, the FASB issued ASU 2017-07, Compensation-Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost. The amendment requires an employer to report the service cost component of net benefit cost in the same line item as other compensation costs arising from services rendered by the pertinent employees during the period. The other components of net benefit cost are required to be presented in the income statement separately from the service cost component and outside a subtotal of income from operations. In addition, the amendment allows only the service cost component to be eligible for capitalization when applicable. The Company adopted the amendment in the first quarter of 2018. Adoption did not have a material impact on the Company's consolidated financial statements. Standards to be implemented The Company is evaluating the impact that the below standards to be implemented will have on the Company's consolidated financial statements. In February 2016, FASB issued ASU 2016-02, Leases (Topic 842). The amendment increases transparency and comparability among organizations by recognizing lease assets and lease liabilities on the balance sheet and disclosing key information about leasing arrangements. In February 2018, FASB issued ASU 2018-01, Leases (Topic 842): Land Easement Practical Expedient for Transition to Topic 842. The amendment clarifies that land easements are within the scope of the new leases standard (ASC 842) and introduces a new transition practical expedient allowing a company to not assess whether existing and expired land easements that were not previously accounted for as leases under current US GAAP (ASC 840) are or contain leases under ASC 842. The Company will adopt the new standard beginning on January 1, 2019. A modified retrospective transition approach is required for leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements, with certain practical expedients available. While the Company is still continuing to assess the effect of adoption, it expects that the new standard will have a material effect on its consolidated balance sheet related to the recognition of new assets and lease liabilities. In preparation for the adoption of the guidance, the Company is in the process of implementing new software to enable the preparation of financial information.

REVENUES (Tables)

3 Months Ended

Mar. 31, 2018

Revenue from Contract with Customer [Abstract]

Disaggregation of Revenue

The following table presents our revenues disaggregated by revenue source (in thousands):



	Three Months Ended March 31, 2018
	Environmental Services		Safety-Kleen		Corporate		Total
Primary Geographical Markets
United States	$	343,972	$	287,642	$	145	$	631,759
Canada	95,716		22,276		27		118,019
	439,688		309,918		172		749,778
Sources of Revenue (1)
Technical Services	236,306		—		—		236,306
Field and Emergency Response Services	69,935		—		—		69,935
Industrial Services	103,763		—		—		103,763
Oil, Gas and Lodging Services and Other	29,684		—		172		29,856
Safety-Kleen Environmental Services	—		194,161		—		194,161
Kleen Performance Products	—		115,757		—		115,757
Total third party revenues	$	439,688	$	309,918	$	172	$	749,778



	Three Months Ended March 31, 2017
	Environmental Services		Safety-Kleen		Corporate		Total
Primary Geographical Markets
United States	$	313,783	$	272,071	$	133	$	585,987
Canada	82,124		20,830		—		102,954
	395,907		292,901		133		688,941
Sources of Revenue (1)
Technical Services	230,218		—		—		230,218
Field and Emergency Response Services	61,019		—		—		61,019
Industrial Services	75,068		—		—		75,068
Oil, Gas and Lodging Services and Other	29,602		—		133		29,735
Safety-Kleen Environmental Services	—		191,727		—		191,727
Kleen Performance Products	—		101,174		—		101,174
Total third party revenues	$	395,907	$	292,901	$	133	$	688,941

______________________


1.	All revenue except Kleen Performance Products and product sales within Safety-Kleen Environmental Services, including allied products and direct blended oil sales, are recognized over time. Kleen Performance Products and Safety-Kleen Environmental Services product revenues are recognized at a point in time.

Contract Balances



	March 31, 2018		December 31, 2017		March 31, 2017		December 31, 2016
Receivables	$	551,841	$	528,924	$	480,044	$	496,226
Contract Assets	63,375		35,922		28,106		36,190
Contract Liabilities	68,748		67,822		64,379		64,397

BUSINESS COMBINATIONS (Tables)

3 Months Ended

Mar. 31, 2018

Business Combinations [Abstract]

Schedule of Business Acquisitions, by Acquisition

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



	At Acquisition Date
Accounts receivable, including unbilled receivables	$	40,773
Inventories and supplies	1,442
Prepaid expenses and other current assets	1,005
Property, plant and equipment	72,244
Permits and other intangibles	5,140
Current liabilities	(15,908		)
Closure and post-closure liabilities	(604		)
Total identifiable net assets	104,092
Goodwill	15,908
Total purchase price, net of cash acquired	$	120,000

DISPOSITION OF BUSINESS (Tables)

3 Months Ended

Mar. 31, 2018

Transformer Services

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Disposition of Business



	Three Months Ended
	March 31, 2017
Income before provision for income taxes	$	898

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=65878427&loc=SL51721533-107759

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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-Paragraph 3A
-URI http://asc.fasb.org/extlink&oid=84176398&loc=SL51724579-110230

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-Paragraph 5C
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Reference 9: http://www.xbrl.org/2003/role/presentationRef
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-URI http://asc.fasb.org/extlink&oid=64827811&loc=SL51721677-107760

+ Details

INVENTORIES AND SUPPLIES (Tables)

3 Months Ended

Mar. 31, 2018

Inventory Disclosure [Abstract]

Schedule of Inventory

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



	March 31, 2018		December 31, 2017
Oil and oil products	$	59,243	$	58,142
Supplies and drums	97,246		94,242
Solvent and solutions	9,188		9,167
Modular camp accommodations	2,247		1,826
Other	13,514		12,635
Total inventories and supplies	$	181,438	$	176,012

PROPERTY, PLANT AND EQUIPMENT (Tables)

3 Months Ended

Mar. 31, 2018

Property, Plant and Equipment [Abstract]

Property, Plant and Equipment

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



	March 31, 2018		December 31, 2017
Land	$	124,331	$	121,658
Asset retirement costs (non-landfill)	14,794		14,593
Landfill assets	145,177		144,539
Buildings and improvements	421,749		414,384
Camp equipment	165,104		170,012
Vehicles	676,749		617,959
Equipment	1,659,335		1,644,102
Furniture and fixtures	5,656		5,708
Construction in progress	47,034		57,618
	3,259,929		3,190,573
Less - accumulated depreciation and amortization	1,628,281		1,603,208
Total property, plant and equipment, net	$	1,631,648	$	1,587,365

GOODWILL AND OTHER INTANGIBLE ASSETS (Tables)

3 Months Ended

Mar. 31, 2018

Goodwill and Intangible Assets Disclosure [Abstract]

Schedule of changes to goodwill

The changes in goodwill by segment for the three months ended March 31, 2018 were as follows (in thousands):



	Environmental Services			Safety-Kleen			Totals
Balance at January 1, 2018	$	172,386		$	306,137		$	478,523
Increase from current period acquisition	15,908			—			15,908
Measurement period adjustments from prior period acquisitions	(9		)	—			(9		)
Foreign currency translation	(795		)	(922		)	(1,717		)
Balance at March 31, 2018	$	187,490		$	305,215		$	492,705

Summary of indefinite-lived intangible assets

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



	March 31, 2018						December 31, 2017
	Cost		Accumulated Amortization		Net		Cost		Accumulated Amortization		Net
Permits	$	174,867	$	75,493	$	99,374	$	174,721	$	74,347	$	100,374
Customer and supplier relationships	400,385		165,056		235,329		399,224		158,972		240,252
Other intangible assets	38,071		31,170		6,901		36,766		31,592		5,174
Total amortizable permits and other intangible assets	613,323		271,719		341,604		610,711		264,911		345,800
Indefinite lived trademarks and trade names	123,031		—		123,031		123,328		—		123,328
Total permits and other intangible assets	$	736,354	$	271,719	$	464,635	$	734,039	$	264,911	$	469,128

Schedule of finite-lived intangible assets

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



	March 31, 2018						December 31, 2017
	Cost		Accumulated Amortization		Net		Cost		Accumulated Amortization		Net
Permits	$	174,867	$	75,493	$	99,374	$	174,721	$	74,347	$	100,374
Customer and supplier relationships	400,385		165,056		235,329		399,224		158,972		240,252
Other intangible assets	38,071		31,170		6,901		36,766		31,592		5,174
Total amortizable permits and other intangible assets	613,323		271,719		341,604		610,711		264,911		345,800
Indefinite lived trademarks and trade names	123,031		—		123,031		123,328		—		123,328
Total permits and other intangible assets	$	736,354	$	271,719	$	464,635	$	734,039	$	264,911	$	469,128

Schedule of expected amortization for the net carrying amount of finite lived intangible assets

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



Years Ending December 31,	Expected Amortization
2018 (nine months)	$	26,018
2019	32,247
2020	29,486
2021	27,492
2022	27,342
Thereafter	199,019
	$	341,604

CLOSURE AND POST-CLOSURE LIABILITIES (Tables)

3 Months Ended

Mar. 31, 2018

Asset Retirement Obligation Disclosure [Abstract]

Schedule of closure and post-closure liabilities

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



	Landfill Retirement Liability			Non-Landfill Retirement Liability			Total
Balance at January 1, 2018	$	32,382		$	28,655		$	61,037
Liabilities assumed in acquisition	—			604			604
New asset retirement obligations	1,053			—			1,053
Accretion	646			619			1,265
Changes in estimates recorded to statement of operations	—			30			30
Changes in estimates recorded to balance sheet	441			—			441
Expenditures	(155		)	(62		)	(217		)
Currency translation and other	(78		)	(55		)	(133		)
Balance at March 31, 2018	$	34,289		$	29,791		$	64,080

REMEDIAL LIABILITIES (Tables)

3 Months Ended

Mar. 31, 2018

Environmental Remediation Obligations [Abstract]

Changes to remedial liabilities

The changes to remedial liabilities for the three months ended March 31, 2018 were as follows (in thousands):



	Remedial Liabilities for Landfill Sites			Remedial Liabilities for Inactive Sites			Remedial Liabilities (Including Superfund) for Non-Landfill Operations			Total
Balance at January 1, 2018	$	1,800		$	65,342		$	57,326		$	124,468
Accretion	21			672			472			1,165
Changes in estimates recorded to statement of operations	—			(24		)	(568		)	(592		)
Expenditures	(12		)	(826		)	(1,370		)	(2,208		)
Currency translation and other	—			(9		)	(377		)	(386		)
Balance at March 31, 2018	$	1,809		$	65,155		$	55,483		$	122,447

FINANCING ARRANGEMENTS (Tables)

3 Months Ended

Mar. 31, 2018

Debt Disclosure [Abstract]

Summary of the entity's financial arrangements

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



	March 31, 2018			December 31, 2017
Senior secured Term Loan Agreement ("Term Loan Agreement")	$	4,000		$	4,000
Current portion of long-term obligations, at carrying value	$	4,000		$	4,000

Senior secured Term Loan Agreement due June 30, 2024	$	393,000		$	394,000
Senior unsecured notes, at 5.25%, due August 1, 2020 ("2020 Notes")	400,000			400,000
Senior unsecured notes, at 5.125%, due June 1, 2021 ("2021 Notes")	845,000			845,000
Long-term obligations, at par	$	1,638,000		$	1,639,000
Unamortized debt issuance costs and premium, net	(12,741		)	(13,463		)
Long-term obligations, at carrying value	$	1,625,259		$	1,625,537

Total current and long-term obligations, at carrying value	$	1,629,259		$	1,629,537

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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+ Details

LOSS PER SHARE (Tables)

3 Months Ended

Mar. 31, 2018

Earnings Per Share [Abstract]

Reconciliation of basic and diluted earnings per share computations

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



	Three Months Ended
	March 31,
	2018			2017
Numerator for basic and diluted loss per share:
Net loss	$	(12,631	)	$	(21,393	)

Denominator:
Basic shares outstanding	56,457			57,262
Dilutive effect of equity-based compensation awards	—			—
Dilutive shares outstanding	56,457			57,262

Basic loss per share:	$	(0.22	)	$	(0.37	)

Diluted loss per share:	$	(0.22	)	$	(0.37	)

ACCUMULATED OTHER COMPREHENSIVE LOSS (Tables)

3 Months Ended

Mar. 31, 2018

Equity [Abstract]

Schedule of accumulated other comprehensive loss

The changes in accumulated other comprehensive loss by component and related tax effects for the three months ended March 31, 2018 were as follows (in thousands):



	Foreign Currency Translation			Unrealized Losses on Available-For-Sale Securities			Unfunded Pension Liability			Total
Balance at January 1, 2018	$	(170,575	)	$	(146	)	$	(1,686	)	$	(172,407	)
Other comprehensive loss before tax effects	(16,551		)	(115		)	—			(16,666		)
Tax effects	—			(80		)	—			(80		)
Other comprehensive loss	$	(16,551	)	$	(195	)	$	—		$	(16,746	)
Balance at March 31, 2018	$	(187,126	)	$	(341	)	$	(1,686	)	$	(189,153	)

STOCK-BASED COMPENSATION (Tables)

3 Months Ended

Mar. 31, 2018

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

Summary of restricted stock awards

The following table summarizes information about restricted stock awards for the three months ended March 31, 2018:



Restricted Stock	Number of Shares		Weighted Average Grant-Date Fair Value
Balance at January 1, 2018	604,933		$	54.23
Granted	149,200		$	53.43
Vested	(25,558	)	$	52.65
Forfeited	(6,772	)	$	52.65
Balance at March 31, 2018	721,803		$	54.13

Summary of performance stock awards

The following table summarizes information about performance stock awards for the three months ended March 31, 2018:



Performance Stock	Number of Shares		Weighted Average Grant-Date Fair Value
Balance at January 1, 2018	190,129		$	55.63
Granted	—		$	—
Vested	(8,696	)	$	54.26
Forfeited	(7,056	)	$	54.64
Balance at March 31, 2018	174,377		$	55.74

SEGMENT REPORTING (Tables)

3 Months Ended

Mar. 31, 2018

Segment Reporting [Abstract]

Reconciliation of third party revenues to direct revenues

The following table reconciles third party revenues to direct revenues for the three months ended March 31, 2018 and 2017 (in thousands):



	For the Three Months Ended March 31, 2018											For the Three Months Ended March 31, 2017
	Third party revenues		Intersegment revenues, net			Corporate Items, net			Direct revenues			Third party revenues		Intersegment revenues, net			Corporate Items, net			Direct revenues
Environmental Services	$	439,688	$	31,965		$	794		$	472,447		$	395,907	$	32,069		$	920		$	428,896
Safety-Kleen	309,918		(31,965		)	11			277,964			292,901		(32,069		)	3			260,835
Corporate Items	172		—			(805		)	(633		)	133		—			(923		)	(790		)
Total	$	749,778	$	—		$	—		$	749,778		$	688,941	$	—		$	—		$	688,941

Reconciliation to consolidated statements of income from adjusted EBITDA

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



	For the Three Months Ended
	March 31,
	2018			2017
Adjusted EBITDA:
Environmental Services	$	61,417		$	60,190
Safety-Kleen	61,884			52,368
Corporate Items	(35,036		)	(32,423		)
Total	$	88,265		$	80,135
Reconciliation to Consolidated Statements of Operations:
Accretion of environmental liabilities	2,430			2,290
Depreciation and amortization	74,844			72,412
Income from operations	10,991			5,433
Other expense, net	299			1,549
Interest expense, net of interest income	20,270			22,576
Loss before provision for income taxes	$	(9,578	)	$	(18,692	)

PP&E, intangible assets and total assets by segment

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



	March 31, 2018
	Environmental Services		Safety-Kleen		Corporate Items		Totals
Property, plant and equipment, net	$	998,340	$	553,308	$	80,000	$	1,631,648
Goodwill	187,490		305,215		—		492,705
Permits and other intangibles, net	99,401		365,234		—		464,635
Total assets	$	1,685,168	$	1,437,026	$	562,622	$	3,684,816



	December 31, 2017
	Environmental Services		Safety-Kleen		Corporate Items		Totals
Property, plant and equipment, net	$	927,139	$	582,162	$	78,064	$	1,587,365
Goodwill	172,386		306,137		—		478,523
Permits and other intangibles, net	97,519		371,609		—		469,128
Total assets	$	1,541,241	$	1,471,291	$	694,038	$	3,706,570

Total assets by geographical area

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



	March 31, 2018		December 31, 2017
United States	$	3,002,779	$	2,985,394
Canada	681,901		721,176
Other foreign	136		—
Total	$	3,684,816	$	3,706,570

GUARANTOR AND NON-GUARANTOR SUBSIDIARIES FINANCIAL INFORMATION (Tables)

3 Months Ended

Mar. 31, 2018

Guarantor and Non-Guarantor Subsidiaries Financial Information [Abstract]

Schedule of condensed consolidating balance sheet

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



	Clean Harbors, Inc.		Guarantor Subsidiaries		Non-Guarantor Subsidiaries		Consolidating Adjustments			Total
Assets:
Cash and cash equivalents	$	51,781	$	99,662	$	34,909	$	—		$	186,352
Short-term marketable securities	—		—		37,792		—			37,792
Intercompany receivables	244,228		600,975		63,875		(909,078		)	—
Accounts receivable, net	—		457,231		94,610		—			551,841
Other current assets	—		265,477		52,050		(13,690		)	303,837
Property, plant and equipment, net	—		1,249,417		382,231		—			1,631,648
Investments in subsidiaries	3,095,335		535,503		—		(3,630,838		)	—
Intercompany debt receivable	—		89,947		21,000		(110,947		)	—
Goodwill	—		431,574		61,131		—			492,705
Permits and other intangibles, net	—		407,887		56,748		—			464,635
Other long-term assets	1,938		12,385		1,695		(12		)	16,006
Total assets	$	3,393,282	$	4,150,058	$	806,041	$	(4,664,565	)	$	3,684,816
Liabilities and Stockholders’ Equity:
Current liabilities	$	22,210	$	382,937	$	133,227	$	(13,690	)	$	524,684
Intercompany payables	600,287		306,401		2,390		(909,078		)	—
Closure, post-closure and remedial liabilities, net	—		149,316		17,388		—			166,704
Long-term obligations, net	1,625,259		—		—		—			1,625,259
Intercompany debt payable	—		21,000		89,947		(110,947		)	—
Other long-term liabilities	—		201,053		21,602		(12		)	222,643
Total liabilities	2,247,756		1,060,707		264,554		(1,033,727		)	2,539,290
Stockholders’ equity	1,145,526		3,089,351		541,487		(3,630,838		)	1,145,526
Total liabilities and stockholders’ equity	$	3,393,282	$	4,150,058	$	806,041	$	(4,664,565	)	$	3,684,816

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



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

Schedule of condensed consolidating statement of income

Following is the consolidating statement of operations for the three months ended March 31, 2018 (in thousands):



	Clean Harbors, Inc.			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating Adjustments			Total
Revenues
Service revenues	$	—		$	481,483		$	152,401		$	(14,165	)	$	619,719
Product revenues	—			121,582			11,450			(2,973		)	130,059
Total revenues	—			603,065			163,851			(17,138		)	749,778
Cost of revenues (exclusive of items shown separately below)
Service cost of revenues	—			328,180			133,634			(14,165		)	447,649
Product cost of revenues	—			95,038			6,711			(2,973		)	98,776
Total cost of revenues	—			423,218			140,345			(17,138		)	546,425
Selling, general and administrative expenses	35			93,843			21,210			—			115,088
Accretion of environmental liabilities	—			2,176			254			—			2,430
Depreciation and amortization	—			53,704			21,140			—			74,844
(Loss) income from operations	(35		)	30,124			(19,098		)	—			10,991
Other expense, net	—			(85		)	(214		)	—			(299		)
Interest (expense) income, net	(20,999		)	505			224			—			(20,270		)
Equity in earnings of subsidiaries, net of taxes	2,514			(20,062		)	—			17,548			—
Intercompany interest income (expense)	—			1,361			(1,361		)	—			—
(Loss) income before (benefit) provision for income taxes	(18,520		)	11,843			(20,449		)	17,548			(9,578		)
(Benefit) provision for income taxes	(5,889		)	9,101			(159		)	—			3,053
Net (loss) income	(12,631		)	2,742			(20,290		)	17,548			(12,631		)
Other comprehensive loss	(16,746		)	(16,746		)	(14,007		)	30,753			(16,746		)
Comprehensive loss	$	(29,377	)	$	(14,004	)	$	(34,297	)	$	48,301		$	(29,377	)

Following is the consolidating statement of operations for the three months ended March 31, 2017 (in thousands):



	Clean Harbors, Inc.			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating Adjustments			Total
Revenues
Service revenues	$	—		$	443,305		$	131,071		$	(14,162	)	$	560,214
Product revenues	—			116,650			15,331			(3,254		)	128,727
Total revenues	—			559,955			146,402			(17,416		)	688,941
Cost of revenues (exclusive of items shown separately below)
Service cost of revenues	—			294,145			111,104			(14,162		)	391,087
Product cost of revenues	—			96,505			12,247			(3,254		)	105,498
Total cost of revenues	—			390,650			123,351			(17,416		)	496,585
Selling, general and administrative expenses	24			92,171			20,026			—			112,221
Accretion of environmental liabilities	—			2,055			235			—			2,290
Depreciation and amortization	—			51,900			20,512			—			72,412
(Loss) income from operations	(24		)	23,179			(17,722		)	—			5,433
Other expense, net	(146		)	(1,389		)	(14		)	—			(1,549		)
Interest (expense) income, net	(22,659		)	119			(36		)	—			(22,576		)
Equity in earnings of subsidiaries, net of taxes	(7,637		)	(21,824		)	—			29,461			—
Intercompany interest income (expense)	—			1,297			(1,297		)	—			—
(Loss) income before (benefit) provision for income taxes	(30,466		)	1,382			(19,069		)	29,461			(18,692		)
(Benefit) provision for income taxes	(9,073		)	9,637			2,137			—			2,701
Net loss	(21,393		)	(8,255		)	(21,206		)	29,461			(21,393		)
Other comprehensive income	6,051			6,051			5,032			(11,083		)	6,051
Comprehensive loss	$	(15,342	)	$	(2,204	)	$	(16,174	)	$	18,378		$	(15,342	)

Schedule of condensed consolidating statement of cash flows

Following is the condensed consolidating statement of cash flows for the three months ended March 31, 2018 (in thousands):



	Clean Harbors, Inc.			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating Adjustments			Total
Net cash from (used in) operating activities	$	143		$	69,536		$	(17,776	)	$	—		$	51,903
Cash flows used in investing activities:
Additions to property, plant and equipment	—			(37,319		)	(6,923		)	—			(44,242		)
Proceeds from sale and disposal of fixed assets	—			292			506			—			798
Acquisitions, net of cash acquired	—			(120,000		)	—			—			(120,000		)
Additions to intangible assets, including costs to obtain or renew permits	—			(1,234		)	(11		)	—			(1,245		)
Proceeds from sale of available-for-sale securities	—			—			3,264			—			3,264
Purchases of available-for-sale securities	—			—			(3,003		)	—			(3,003		)
Intercompany	—			(15,812		)	—			15,812			—
Net cash used in investing activities	—			(174,073		)	(6,167		)	15,812			(164,428		)

Cash flows used in financing activities:
Change in uncashed checks	—			(3,578		)	(265		)	—			(3,843		)
Tax payments related to withholdings on vested restricted stock	(548		)	—			—			—			(548		)
Repurchases of common stock	(14,264		)	—			—			—			(14,264		)
Principal payment on debt	(1,000		)	—			—			—			(1,000		)
Intercompany	15,812			—			—			(15,812		)	—
Net cash used in financing activities	—			(3,578		)	(265		)	(15,812		)	(19,655		)
Effect of exchange rate change on cash	—			—			(867		)	—			(867		)
Increase (decrease) in cash and cash equivalents	143			(108,115		)	(25,075		)	—			(133,047		)
Cash and cash equivalents, beginning of period	51,638			207,777			59,984			—			319,399
Cash and cash equivalents, end of period	$	51,781		$	99,662		$	34,909		$	—		$	186,352

Following is the condensed consolidating statement of cash flows for the three months ended March 31, 2017 (in thousands):



	Clean Harbors, Inc.			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating Adjustments			Total
Net cash (used in) from operating activities	$	(1,663	)	$	41,144		$	17,638		$	—		$	57,119
Cash flows from (used in) investing activities:
Additions to property, plant and equipment	—			(33,136		)	(9,326		)	—			(42,462		)
Proceeds from sale and disposal of fixed assets	—			664			366			—			1,030
Acquisitions, net of cash acquired	—			(11,946		)	—			—			(11,946		)
Proceeds from sale of business	1,837			—			181			—			2,018
Additions to intangible assets, including costs to obtain or renew permits	—			(573		)	(178		)	—			(751		)
Proceeds from sale of investments	243			—			—			—			243
Intercompany	—			(7,771		)	—			7,771			—
Net cash from (used in) investing activities	2,080			(52,762		)	(8,957		)	7,771			(51,868		)

Cash flows used in financing activities:
Change in uncashed checks	—			(5,165		)	(2,392		)	—			(7,557		)
Proceeds from exercise of stock options	46			—			—			—			46
Tax payments related to withholdings on vested restricted stock	(1,021		)	—			—			—			(1,021		)
Repurchases of common stock	(6,796		)	—			—			—			(6,796		)
Deferred financing costs paid	(108		)	—			—			—			(108		)
Intercompany	7,771			—			—			(7,771		)	—
Net cash used in financing activities	(108		)	(5,165		)	(2,392		)	(7,771		)	(15,436		)
Effect of exchange rate change on cash	—			—			554			—			554
Increase (decrease) in cash and cash equivalents	309			(16,783		)	6,843			—			(9,631		)
Cash and cash equivalents, beginning of period	51,417			155,943			99,637			—			306,997
Cash and cash equivalents, end of period	$	51,726		$	139,160		$	106,480		$	—		$	297,366

SIGNIFICANT ACCOUNTING POLICIES (Narrative) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) segment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of operating segments \| segment	2
Cumulative effect of change in accounting principle	$ 1,564
Accumulated Earnings \| Accounting Standards Update 2016-16
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of change in accounting principle	$ 1,564

REVENUES (Disaggregation of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Revenues	$ 749,778	$ 688,941
United States
Disaggregation of Revenue [Line Items]
Revenues	631,759	585,987
Canada
Disaggregation of Revenue [Line Items]
Revenues	118,019	102,954
Technical Services
Disaggregation of Revenue [Line Items]
Revenues	236,306	230,218
Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Revenues	69,935	61,019
Industrial Services
Disaggregation of Revenue [Line Items]
Revenues	103,763	75,068
Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Revenues	29,856	29,735
Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Revenues	194,161	191,727
Kleen Performance Products
Disaggregation of Revenue [Line Items]
Revenues	115,757	101,174
Environmental Services
Disaggregation of Revenue [Line Items]
Revenues	439,688	395,907
Environmental Services \| United States
Disaggregation of Revenue [Line Items]
Revenues	343,972	313,783
Environmental Services \| Canada
Disaggregation of Revenue [Line Items]
Revenues	95,716	82,124
Environmental Services \| Technical Services
Disaggregation of Revenue [Line Items]
Revenues	236,306	230,218
Environmental Services \| Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Revenues	69,935	61,019
Environmental Services \| Industrial Services
Disaggregation of Revenue [Line Items]
Revenues	103,763	75,068
Environmental Services \| Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Revenues	29,684	29,602
Environmental Services \| Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Revenues	0	0
Environmental Services \| Kleen Performance Products
Disaggregation of Revenue [Line Items]
Revenues	0	0
Safety-Kleen
Disaggregation of Revenue [Line Items]
Revenues	309,918	292,901
Safety-Kleen \| United States
Disaggregation of Revenue [Line Items]
Revenues	287,642	272,071
Safety-Kleen \| Canada
Disaggregation of Revenue [Line Items]
Revenues	22,276	20,830
Safety-Kleen \| Technical Services
Disaggregation of Revenue [Line Items]
Revenues	0	0
Safety-Kleen \| Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Revenues	0	0
Safety-Kleen \| Industrial Services
Disaggregation of Revenue [Line Items]
Revenues	0	0
Safety-Kleen \| Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Revenues	0	0
Safety-Kleen \| Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Revenues	194,161	191,727
Safety-Kleen \| Kleen Performance Products
Disaggregation of Revenue [Line Items]
Revenues	115,757	101,174
Corporate Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	172	133
Corporate Segment [Member] \| United States
Disaggregation of Revenue [Line Items]
Revenues	145	133
Corporate Segment [Member] \| Canada
Disaggregation of Revenue [Line Items]
Revenues	27	0
Corporate Segment [Member] \| Technical Services
Disaggregation of Revenue [Line Items]
Revenues	0	0
Corporate Segment [Member] \| Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Revenues	0	0
Corporate Segment [Member] \| Industrial Services
Disaggregation of Revenue [Line Items]
Revenues	0	0
Corporate Segment [Member] \| Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Revenues	172	133
Corporate Segment [Member] \| Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Revenues	0	0
Corporate Segment [Member] \| Kleen Performance Products
Disaggregation of Revenue [Line Items]
Revenues	$ 0	$ 0

REVENUES (Contract Balances) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Revenue from Contract with Customer [Abstract]
Receivables	$ 551,841	$ 528,924	$ 480,044	$ 496,226
Contract Assets	63,375	35,922	28,106	36,190
Contract Liabilities	$ 68,748	$ 67,822	$ 64,379	$ 64,397

REVENUES (Narrative) (Details) - Veolia Division $ in Millions	Feb. 23, 2018 USD ($)
Business Acquisition [Line Items]
Acquired receivables	$ 22.1
Customer contracts
Business Acquisition [Line Items]
Acquired contract assets	$ 18.7

BUSINESS COMBINATIONS (2018 Acquisition) (Details) - Veolia Division - USD ($) $ in Millions		3 Months Ended
	Feb. 23, 2018	Mar. 31, 2018
Business Acquisition [Line Items]
Purchase price	$ 120.0
Revenue from acquisition included in results of operations		$ 17.6
Acquisition-related costs		$ 0.5
Weighted average amortization period (in years)	8 years 2 months

BUSINESS COMBINATIONS (Assets Acquired and Liabilities Assumed) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Feb. 23, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Goodwill	$ 492,705		$ 478,523
Veolia Division
Business Acquisition [Line Items]
Accounts receivable		$ 40,773
Inventories and supplies		1,442
Prepaid and other current assets		1,005
Property, plant and equipment		72,244
Permits and other intangibles		5,140
Current liabilities		(15,908)
Closure and post-closure liabilities		(604)
Total identifiable net assets		104,092
Goodwill		15,908
Total purchase price, net of cash acquired		$ 120,000

BUSINESS COMBINATIONS (2017 Acquisitions) (Details) $ / shares in Units, $ in Thousands, $ in Millions						3 Months Ended
	Oct. 16, 2017 USD ($)	Sep. 22, 2017 USD ($)	Jul. 14, 2017 CAD ($) $ / shares	Jul. 14, 2017 USD ($)	Jan. 31, 2017 USD ($)	Mar. 31, 2018 USD ($)	Jul. 14, 2017 USD ($)
Business Acquisition [Line Items]
Goodwill recognized						$ 15,908
Washer Machines and Related Equipment
Business Acquisition [Line Items]
Purchase price		$ 2,100
Goodwill recognized		$ 700
Lonestar
Business Acquisition [Line Items]
Goodwill recognized				$ 2,900
Cash paid to acquire Lonestar			$ 41.8	$ 33,100
Equity payout (in CAD per share) \| $ / shares			$ 0.72
Debt outstanding assumed			$ 21.3				$ 16,800
2017 Acquisitions
Business Acquisition [Line Items]
Purchase price	$ 4,800				$ 11,900
Goodwill recognized					$ 5,000

DISPOSITION OF BUSINESS (Narrative) (Details) $ in Millions	Jun. 30, 2017 USD ($)
Catalyst Services \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Final sale proceeds	$ 45.5

DISPOSITION OF BUSINESS (Income (Loss) Attributable to Transformer Services) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($)
Transformer Services \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income before provision for income taxes	$ 898

INVENTORIES AND SUPPLIES (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Oil and oil products	$ 59,243	$ 58,142
Supplies and drums	97,246	94,242
Solvent and solutions	9,188	9,167
Modular camp accommodations	2,247	1,826
Other	13,514	12,635
Total inventories and supplies	$ 181,438	$ 176,012

PROPERTY, PLANT AND EQUIPMENT (Schedule of Property, Plant and Equipment) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	$ 3,259,929	$ 3,190,573
Less - accumulated depreciation and amortization	1,628,281	1,603,208
Total property, plant and equipment, net	1,631,648	1,587,365
Land
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	124,331	121,658
Asset retirement costs (non-landfill)
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	14,794	14,593
Landfill assets
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	145,177	144,539
Buildings and improvements
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	421,749	414,384
Camp equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	165,104	170,012
Vehicles
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	676,749	617,959
Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	1,659,335	1,644,102
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	5,656	5,708
Construction in progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	$ 47,034	$ 57,618

PROPERTY, PLANT AND EQUIPMENT (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Property, Plant and Equipment [Abstract]
Interest costs capitalized adjustment	$ 0.3	$ 0.1
Depreciation inclusive of amortization	$ 65.6	$ 63.3

GOODWILL AND OTHER INTANGIBLE ASSETS (Rollforward of Goodwill) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Goodwill [Roll Forward]
Balance at beginning of year	$ 478,523
Increase from current period acquisition	15,908
Measurement period adjustments from prior period acquisitions	(9)
Foreign currency translation	(1,717)
Balance at end of year	492,705
Environmental Services
Goodwill [Roll Forward]
Balance at beginning of year	172,386
Increase from current period acquisition	15,908
Measurement period adjustments from prior period acquisitions	(9)
Foreign currency translation	(795)
Balance at end of year	187,490
Safety-Kleen
Goodwill [Roll Forward]
Balance at beginning of year	306,137
Increase from current period acquisition	0
Measurement period adjustments from prior period acquisitions	0
Foreign currency translation	(922)
Balance at end of year	$ 305,215

GOODWILL AND OTHER INTANGIBLE ASSETS (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization of permits and other intangible assets	$ 9.2	$ 9.1

GOODWILL AND OTHER INTANGIBLE ASSETS (Amortizable Other Intangible Assets) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Finite-lived and Indefinite-lived Intangible Assets [Line Items]
Cost	$ 613,323	$ 610,711
Accumulated Amortization	271,719	264,911
Net	341,604	345,800
Total permits and other intangible assets, Cost	736,354	734,039
Total permits and other intangible assets, Net	464,635	469,128
Indefinite lived trademarks and trade names
Schedule of Finite-lived and Indefinite-lived Intangible Assets [Line Items]
Indefinite lived trademarks and trade names	123,031	123,328
Permits
Schedule of Finite-lived and Indefinite-lived Intangible Assets [Line Items]
Cost	174,867	174,721
Accumulated Amortization	75,493	74,347
Net	99,374	100,374
Customer and supplier relationships
Schedule of Finite-lived and Indefinite-lived Intangible Assets [Line Items]
Cost	400,385	399,224
Accumulated Amortization	165,056	158,972
Net	235,329	240,252
Other intangible assets
Schedule of Finite-lived and Indefinite-lived Intangible Assets [Line Items]
Cost	38,071	36,766
Accumulated Amortization	31,170	31,592
Net	$ 6,901	$ 5,174

GOODWILL AND OTHER INTANGIBLE ASSETS (Expected Future Amortization) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
2018 (nine months)	$ 26,018
2019	32,247
2020	29,486
2021	27,492
2022	27,342
Thereafter	199,019
Net	$ 341,604	$ 345,800

ACCRUED EXPENSES (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Payables and Accruals [Abstract]
Insurance	$ 63,966	$ 57,889
Interest	18,274	12,660
Accrued compensation and benefits	48,253	55,861
Income, real estate, sales and other taxes	28,803	27,330
Other	34,864	34,242
Total accrued expenses	$ 194,160	$ 187,982

CLOSURE AND POST-CLOSURE LIABILITIES (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Changes to post-closure liabilities
Beginning balance	$ 61,037
Liabilities assumed in acquisition	604
New asset retirement obligations	1,053
Accretion	1,265
Changes in estimates recorded to statement of operations	30
Changes in estimates recorded to balance sheet	441
Expenditures	(217)
Currency translation and other	(133)
Ending balance	$ 64,080
Credit-adjusted risk-free rate	5.66%
Landfill Retirement Liability
Changes to post-closure liabilities
Beginning balance	$ 32,382
Liabilities assumed in acquisition	0
New asset retirement obligations	1,053
Accretion	646
Changes in estimates recorded to statement of operations	0
Changes in estimates recorded to balance sheet	441
Expenditures	(155)
Currency translation and other	(78)
Ending balance	34,289
Non-Landfill Retirement Liability
Changes to post-closure liabilities
Beginning balance	28,655
Liabilities assumed in acquisition	604
New asset retirement obligations	0
Accretion	619
Changes in estimates recorded to statement of operations	30
Changes in estimates recorded to balance sheet	0
Expenditures	(62)
Currency translation and other	(55)
Ending balance	$ 29,791

REMEDIAL LIABILITIES (Details) $ in Thousands	3 Months Ended
REMEDIAL LIABILITIES (Details) $ in Thousands	Mar. 31, 2018 USD ($)
Accrual for Environmental Loss Contingencies [Roll Forward]
Balance at beginning of year	$ 124,468
Accretion	1,165
Changes in estimates recorded to statement of operations	(592)
Expenditures	(2,208)
Currency translation and other	(386)
Balance at end of year	122,447
Remedial Liabilities for Landfill Sites
Accrual for Environmental Loss Contingencies [Roll Forward]
Balance at beginning of year	1,800
Accretion	21
Changes in estimates recorded to statement of operations	0
Expenditures	(12)
Currency translation and other	0
Balance at end of year	1,809
Remedial Liabilities for Inactive Sites
Accrual for Environmental Loss Contingencies [Roll Forward]
Balance at beginning of year	65,342
Accretion	672
Changes in estimates recorded to statement of operations	(24)
Expenditures	(826)
Currency translation and other	(9)
Balance at end of year	65,155
Remedial Liabilities (Including Superfund) for Non-Landfill Operations
Accrual for Environmental Loss Contingencies [Roll Forward]
Balance at beginning of year	57,326
Accretion	472
Changes in estimates recorded to statement of operations	(568)
Expenditures	(1,370)
Currency translation and other	(377)
Balance at end of year	$ 55,483

FINANCING ARRANGEMENTS (Summary of Financing Arrangements) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Current portion of long-term obligations	$ 4,000	$ 4,000
Long-term obligations, at par	1,638,000	1,639,000
Unamortized debt issuance costs and premium, net	(12,741)	(13,463)
Long-term obligations, at carrying value	1,625,259	1,625,537
Total current and long-term obligations, at carrying value	1,629,259	1,629,537
Secured debt \| Term Loan Agreement
Debt Instrument [Line Items]
Current portion of long-term obligations	4,000	4,000
Long-term obligations, at par	393,000	394,000
Unsecured debt \| Senior unsecured notes, at 5.25%, due August 1, 2020 (2020 Notes)
Debt Instrument [Line Items]
Long-term obligations, at par	$ 400,000	400,000
Interest rate	5.25%
Unsecured debt \| Senior unsecured notes, at 5.125%, due June 1, 2021 (2021 Notes)
Debt Instrument [Line Items]
Long-term obligations, at par	$ 845,000	$ 845,000
Interest rate	5.125%

FINANCING ARRANGEMENTS (Narrative) (Details)	Apr. 17, 2018	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Outstanding loan balances		$ 0	$ 0
Available to borrow and outstanding letters of credit		237,000,000	217,800,000
Outstanding letters of credit		132,900,000	134,100,000
Secured debt \| Term Loan Agreement
Debt Instrument [Line Items]
Debt fair value		$ 398,200,000	400,500,000
Unsecured debt \| Senior unsecured notes, at 5.25%, due August 1, 2020 (2020 Notes)
Debt Instrument [Line Items]
Interest rate		5.25%
Debt fair value		$ 401,600,000	404,600,000
Unsecured debt \| Senior unsecured notes, at 5.125%, due June 1, 2021 (2021 Notes)
Debt Instrument [Line Items]
Interest rate		5.125%
Debt fair value		$ 855,300,000	855,700,000
Revolving Credit Facility \| Line of Credit
Debt Instrument [Line Items]
Revolving credit facility maximum borrowing capacity		$ 400,000,000.0	$ 400,000,000.0
Subsequent event \| Eurodollar \| Secured debt \| First Amendment
Debt Instrument [Line Items]
Interest rate	1.75%
Decrease in interest rate	0.0025
Subsequent event \| Base Rate \| Secured debt \| First Amendment
Debt Instrument [Line Items]
Interest rate	0.75%
Decrease in interest rate	0.0025

LOSS PER SHARE (Computation of Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Numerator for basic and diluted loss per share:
Net loss	$ (12,631)	$ (21,393)
Denominator:
Basic shares outstanding (in shares)	56,457	57,262
Dilutive effect of equity-based compensation awards (in shares)	0	0
Dilutive shares outstanding (in shares)	56,457	57,262
Basic loss per share (in USD per share)	$ (0.22)	$ (0.37)
Diluted loss per share (in USD per share)	$ (0.22)	$ (0.37)

LOSS PER SHARE (Narrative) (Details) - shares	3 Months Ended
LOSS PER SHARE (Narrative) (Details) - shares	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Shares excluded from computation of earning per share (in shares)	896,180	659,558

ACCUMULATED OTHER COMPREHENSIVE LOSS (Changes in Accumulated Other Comprehensive Loss by Component) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Components of Other Accumulated Income, Net of Tax [Roll Forward]
Balance at beginning of period	$ 1,188,202
Other comprehensive loss before tax effects	(16,666)
Tax effects	(80)
Other comprehensive income	(16,746)
Balance at end of period	1,145,526
Foreign Currency Translation
Components of Other Accumulated Income, Net of Tax [Roll Forward]
Balance at beginning of period	(170,575)
Other comprehensive loss before tax effects	(16,551)
Tax effects	0
Other comprehensive income	(16,551)
Balance at end of period	(187,126)
Unrealized Losses on Available-For-Sale Securities
Components of Other Accumulated Income, Net of Tax [Roll Forward]
Balance at beginning of period	(146)
Other comprehensive loss before tax effects	(115)
Tax effects	(80)
Other comprehensive income	(195)
Balance at end of period	(341)
Unfunded Pension Liability
Components of Other Accumulated Income, Net of Tax [Roll Forward]
Balance at beginning of period	(1,686)
Other comprehensive loss before tax effects	0
Tax effects	0
Other comprehensive income	0
Balance at end of period	(1,686)
Total
Components of Other Accumulated Income, Net of Tax [Roll Forward]
Balance at beginning of period	(172,407)
Balance at end of period	$ (189,153)

STOCK-BASED COMPENSATION (Narrative) (Details) - USD ($) $ in Thousands, shares in Millions	3 Months Ended		37 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Oct. 31, 2017	Oct. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 3,100	$ 2,300
Income tax benefit	900	$ 800
Shares authorized for repurchase				$ 600,000	$ 300,000
Stock repurchase program, remaining authorized repurchase amount	$ 336,900		$ 336,900
Repurchases of common stock (in shares)	0.3	0.1	5.1
Repurchases of common stock	$ 14,264	$ 6,800	$ 263,100
Restricted stock awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost	$ 28,500		28,500
Period for recognition (in years)	2 years 8 months
Fair value restricted stock	$ 1,300	1,500
Performance stock awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost	2,000		$ 2,000
Fair value restricted stock	$ 500	$ 1,400
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)	3 years
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)	5 years

STOCK-BASED COMPENSATION (Restricted Stock) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Restricted stock awards
Number of Shares
Beginning balance (in shares)	604,933
Granted (in shares)	149,200
Vested (in shares)	(25,558)
Forfeited (in shares)	(6,772)
Ending balance (in shares)	721,803
Weighted Average Grant-Date Fair Value
Beginning of period (in USD per share)	$ 54.23
Granted (in USD per share)	53.43
Vested (in USD per share)	52.65
Forfeited (in USD per share)	52.65
End of period (in USD per share)	$ 54.13
Unrecognized compensation cost	$ 28.5
Period for recognition (in years)	2 years 8 months
Fair value restricted stock	$ 1.3	$ 1.5
Minimum
Weighted Average Grant-Date Fair Value
Vesting period (in years)	3 years
Maximum
Weighted Average Grant-Date Fair Value
Vesting period (in years)	5 years

STOCK-BASED COMPENSATION (Performance Stock Awards (Details) - Performance stock awards - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Number of Shares
Beginning balance (in shares)	190,129
Granted (in shares)	0
Vested (in shares)	(8,696)
Forfeited (in shares)	(7,056)
Ending balance (in shares)	174,377
Weighted Average Grant-Date Fair Value
Beginning of period (in USD per share)	$ 55.63
Granted (in USD per share)	0.00
Vested (in USD per share)	54.26
Forfeited (in USD per share)	54.64
End of period (in USD per share)	$ 55.74
Unrecognized compensation cost	$ 2.0
Fair value restricted stock	$ 0.5	$ 1.4

COMMITMENTS AND CONTINGENCIES (Details) $ in Millions	3 Months Ended	12 Months Ended
COMMITMENTS AND CONTINGENCIES (Details) $ in Millions	Mar. 31, 2018 USD ($) proceeding site claim	Dec. 31, 2012 CAD ($)	Dec. 31, 1999 municipality	Dec. 31, 1968 permit	Dec. 31, 2017 USD ($) proceeding
Contingencies [Line Items]
Recorded reserves for actual or probable liabilities \| $	$ 19,900,000				$ 19,300,000
Number of proceedings as defendant \| proceeding	59
Number of product liability claims settled or dismissed \| claim	3
Legal and Administrative Proceedings
Contingencies [Line Items]
Recorded reserves for actual or probable liabilities \| $	$ 17,800,000				17,900,000
Possible increase in legal and administrative proceedings \| $	$ 1,700,000				1,800,000
Ville Mercier
Contingencies [Line Items]
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
Superfund Proceedings
Contingencies [Line Items]
Number of sites owned by third party excluded from cleanup or related liabilities	127
Number of sites owned by the entity subject to proceedings under federal or state superfund laws	3
Notices received from owners of third party sites seeking indemnification from the company	124
Number of sites for which environmental remediation expense is settled	33
Third party sites requiring expenditure on remediation	16
Number of sites not currently requiring expenditures on remediation	75
Number of sites which potential liability could exceed $100,000	11
Notices received from owners of third party sites seeking indemnification from the company	17
Superfund Proceedings \| Minimum
Contingencies [Line Items]
Minimum potential liability \| $	$ 100,000
ChemWaste
Contingencies [Line Items]
Indemnification agreement with third party sites	11
Kleen Performance Products
Contingencies [Line Items]
Notices received from owners of third party sites seeking indemnification from the company	6
Federal and State Enforcement Actions
Contingencies [Line Items]
Recorded reserves for actual or probable liabilities \| $	$ 2,100,000				$ 1,400,000
Number of proceedings as defendant \| proceeding	5				5
Federal and State Enforcement Actions \| Minimum
Contingencies [Line Items]
Minimum potential liability \| $	$ 100,000				$ 100,000

INCOME TAXES (Details) - USD ($) $ in Millions	3 Months Ended
INCOME TAXES (Details) - USD ($) $ in Millions	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Effective income tax rate	(31.90%)	(14.50%)
Unrecognized tax benefits	$ 5.6		$ 5.1
Interest on unrecognized tax benefits	0.4		$ 0.5
Reduction in unrecognized tax benefits from expiring statue of limitations	$ 1.4

SEGMENT REPORTING (Narrative) (Details)	3 Months Ended
SEGMENT REPORTING (Narrative) (Details)	Mar. 31, 2018 segment
Segment Reporting [Abstract]
Number of operating segments	2

SEGMENT REPORTING (Third Party Revenues to Direct Revenues) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Total revenues	$ 749,778	$ 688,941
Intersegment revenues, net
Segment Reporting Information [Line Items]
Total revenues	0	0
Corporate Items, net
Segment Reporting Information [Line Items]
Total revenues	0	0
Direct revenues
Segment Reporting Information [Line Items]
Total revenues	749,778	688,941
Environmental Services
Segment Reporting Information [Line Items]
Total revenues	439,688	395,907
Environmental Services \| Intersegment revenues, net
Segment Reporting Information [Line Items]
Total revenues	31,965	32,069
Environmental Services \| Corporate Items, net
Segment Reporting Information [Line Items]
Total revenues	794	920
Environmental Services \| Direct revenues
Segment Reporting Information [Line Items]
Total revenues	472,447	428,896
Safety-Kleen
Segment Reporting Information [Line Items]
Total revenues	309,918	292,901
Safety-Kleen \| Intersegment revenues, net
Segment Reporting Information [Line Items]
Total revenues	(31,965)	(32,069)
Safety-Kleen \| Corporate Items, net
Segment Reporting Information [Line Items]
Total revenues	11	3
Safety-Kleen \| Direct revenues
Segment Reporting Information [Line Items]
Total revenues	277,964	260,835
Corporate Items
Segment Reporting Information [Line Items]
Total revenues	172	133
Corporate Items \| Intersegment revenues, net
Segment Reporting Information [Line Items]
Total revenues	0	0
Corporate Items \| Corporate Items, net
Segment Reporting Information [Line Items]
Total revenues	(805)	(923)
Corporate Items \| Direct revenues
Segment Reporting Information [Line Items]
Total revenues	$ (633)	$ (790)

SEGMENT REPORTING (Adjusted EBITDA Information) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ 88,265	$ 80,135
Reconciliation to Consolidated Statements of Operations:
Accretion of environmental liabilities	2,430	2,290
Depreciation and amortization	74,844	72,412
Income from operations	10,991	5,433
Other expense, net	299	1,549
Interest expense, net of interest income	20,270	22,576
(Loss) income before (benefit) provision for income taxes	(9,578)	(18,692)
Environmental Services
Segment Reporting Information [Line Items]
Adjusted EBITDA	61,417	60,190
Safety-Kleen
Segment Reporting Information [Line Items]
Adjusted EBITDA	61,884	52,368
Corporate Items
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ (35,036)	$ (32,423)

SEGMENT REPORTING (Assets by Reportable Segment) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 1,631,648	$ 1,587,365
Goodwill	492,705	478,523
Permits and other intangibles, net	464,635	469,128
Total assets	3,684,816	3,706,570
Environmental Services
Segment Reporting Information [Line Items]
Property, plant and equipment, net	998,340	927,139
Goodwill	187,490	172,386
Permits and other intangibles, net	99,401	97,519
Total assets	1,685,168	1,541,241
Safety-Kleen
Segment Reporting Information [Line Items]
Property, plant and equipment, net	553,308	582,162
Goodwill	305,215	306,137
Permits and other intangibles, net	365,234	371,609
Total assets	1,437,026	1,471,291
Corporate Items
Segment Reporting Information [Line Items]
Property, plant and equipment, net	80,000	78,064
Goodwill	0	0
Permits and other intangibles, net	0	0
Total assets	$ 562,622	$ 694,038

SEGMENT REPORTING (Total Assets by Geographical Area) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Total assets	$ 3,684,816	$ 3,706,570
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Total assets	3,002,779	2,985,394
Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Total assets	681,901	721,176
Other foreign
Revenues from External Customers and Long-Lived Assets [Line Items]
Total assets	$ 136	$ 0

GUARANTOR AND NON-GUARANTOR SUBSIDIARIES FINANCIAL INFORMATION (Condensed Consolidating Balance Sheets) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
ASSETS
Cash and cash equivalents	$ 186,352	$ 319,399	$ 297,366	$ 306,997
Short-term marketable securities	37,792	38,179
Intercompany receivables	0	0
Accounts receivable, net	551,841	528,924
Other current assets	303,837	267,554
Property, plant and equipment, net	1,631,648	1,587,365
Investments in subsidiaries	0	0
Intercompany debt receivable	0	0
Goodwill	492,705	478,523
Permits and other intangibles, net	464,635	469,128
Other long-term assets	16,006	17,498
Total assets	3,684,816	3,706,570
LIABILITIES AND STOCKHOLDERS' EQUITY
Current liabilities	524,684	503,817
Intercompany payables	0	0
Closure, post-closure and remedial liabilities, net	166,704	165,723
Long-term obligations, less current portion	1,625,259	1,625,537
Intercompany debt payable	0	0
Other long-term liabilities	222,643	223,291
Total liabilities	2,539,290	2,518,368
Stockholders’ equity	1,145,526	1,188,202
Total liabilities and stockholders’ equity	3,684,816	3,706,570
Reportable Legal Entities \| Clean Harbors, Inc.
ASSETS
Cash and cash equivalents	51,781	51,638	51,726	51,417
Short-term marketable securities	0	0
Intercompany receivables	244,228	238,339
Accounts receivable, net	0	0
Other current assets	0	897
Property, plant and equipment, net	0	0
Investments in subsidiaries	3,095,335	3,112,547
Intercompany debt receivable	0	0
Goodwill	0	0
Permits and other intangibles, net	0	0
Other long-term assets	1,938	2,084
Total assets	3,393,282	3,405,505
LIABILITIES AND STOCKHOLDERS' EQUITY
Current liabilities	22,210	16,954
Intercompany payables	600,287	574,812
Closure, post-closure and remedial liabilities, net	0	0
Long-term obligations, less current portion	1,625,259	1,625,537
Intercompany debt payable	0	0
Other long-term liabilities	0	0
Total liabilities	2,247,756	2,217,303
Stockholders’ equity	1,145,526	1,188,202
Total liabilities and stockholders’ equity	3,393,282	3,405,505
Reportable Legal Entities \| Guarantor Subsidiaries
ASSETS
Cash and cash equivalents	99,662	207,777	139,160	155,943
Short-term marketable securities	0	0
Intercompany receivables	600,975	590,100
Accounts receivable, net	457,231	433,042
Other current assets	265,477	233,602
Property, plant and equipment, net	1,249,417	1,174,975
Investments in subsidiaries	535,503	569,568
Intercompany debt receivable	89,947	92,530
Goodwill	431,574	415,641
Permits and other intangibles, net	407,887	408,655
Other long-term assets	12,385	12,064
Total assets	4,150,058	4,137,954
LIABILITIES AND STOCKHOLDERS' EQUITY
Current liabilities	382,937	371,135
Intercompany payables	306,401	289,531
Closure, post-closure and remedial liabilities, net	149,316	148,872
Long-term obligations, less current portion	0	0
Intercompany debt payable	21,000	21,000
Other long-term liabilities	201,053	201,086
Total liabilities	1,060,707	1,031,624
Stockholders’ equity	3,089,351	3,106,330
Total liabilities and stockholders’ equity	4,150,058	4,137,954
Reportable Legal Entities \| Non-Guarantor Subsidiaries
ASSETS
Cash and cash equivalents	34,909	59,984	106,480	99,637
Short-term marketable securities	37,792	38,179
Intercompany receivables	63,875	52,909
Accounts receivable, net	94,610	95,882
Other current assets	52,050	52,947
Property, plant and equipment, net	382,231	412,390
Investments in subsidiaries	0	0
Intercompany debt receivable	21,000	21,000
Goodwill	61,131	62,882
Permits and other intangibles, net	56,748	60,473
Other long-term assets	1,695	3,350
Total assets	806,041	859,996
LIABILITIES AND STOCKHOLDERS' EQUITY
Current liabilities	133,227	135,620
Intercompany payables	2,390	17,005
Closure, post-closure and remedial liabilities, net	17,388	16,851
Long-term obligations, less current portion	0	0
Intercompany debt payable	89,947	92,530
Other long-term liabilities	21,602	22,205
Total liabilities	264,554	284,211
Stockholders’ equity	541,487	575,785
Total liabilities and stockholders’ equity	806,041	859,996
Consolidating Adjustments
ASSETS
Cash and cash equivalents	0	0	$ 0	$ 0
Short-term marketable securities	0	0
Intercompany receivables	(909,078)	(881,348)
Accounts receivable, net	0	0
Other current assets	(13,690)	(19,892)
Property, plant and equipment, net	0	0
Investments in subsidiaries	(3,630,838)	(3,682,115)
Intercompany debt receivable	(110,947)	(113,530)
Goodwill	0	0
Permits and other intangibles, net	0	0
Other long-term assets	(12)	0
Total assets	(4,664,565)	(4,696,885)
LIABILITIES AND STOCKHOLDERS' EQUITY
Current liabilities	(13,690)	(19,892)
Intercompany payables	(909,078)	(881,348)
Closure, post-closure and remedial liabilities, net	0	0
Long-term obligations, less current portion	0	0
Intercompany debt payable	(110,947)	(113,530)
Other long-term liabilities	(12)	0
Total liabilities	(1,033,727)	(1,014,770)
Stockholders’ equity	(3,630,838)	(3,682,115)
Total liabilities and stockholders’ equity	$ (4,664,565)	$ (4,696,885)

GUARANTOR AND NON-GUARANTOR SUBSIDIARIES FINANCIAL INFORMATION (Consolidating Statement of Operations) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenues:
Service revenues	$ 619,719	$ 560,214
Product revenues	130,059	128,727
Total revenues	749,778	688,941
Cost of revenues: (exclusive of items shown separately below)
Service cost of revenues	447,649	391,087
Product cost of revenues	98,776	105,498
Total cost of revenues	546,425	496,585
Selling, general and administrative expenses	115,088	112,221
Accretion of environmental liabilities	2,430	2,290
Depreciation and amortization	74,844	72,412
Income from operations	10,991	5,433
Other expense, net	(299)	(1,549)
Interest (expense) income, net	(20,270)	(22,576)
Equity in earnings of subsidiaries, net of taxes	0	0
Intercompany interest income (expense)	0	0
(Loss) income before (benefit) provision for income taxes	(9,578)	(18,692)
(Benefit) provision for income taxes	3,053	2,701
Net loss	(12,631)	(21,393)
Other comprehensive loss	(16,746)	6,051
Comprehensive loss	(29,377)	(15,342)
Reportable Legal Entities \| Clean Harbors, Inc.
Revenues:
Service revenues	0	0
Product revenues	0	0
Total revenues	0	0
Cost of revenues: (exclusive of items shown separately below)
Service cost of revenues	0	0
Product cost of revenues	0	0
Total cost of revenues	0	0
Selling, general and administrative expenses	35	24
Accretion of environmental liabilities	0	0
Depreciation and amortization	0	0
Income from operations	(35)	(24)
Other expense, net	0	(146)
Interest (expense) income, net	(20,999)	(22,659)
Equity in earnings of subsidiaries, net of taxes	2,514	(7,637)
Intercompany interest income (expense)	0	0
(Loss) income before (benefit) provision for income taxes	(18,520)	(30,466)
(Benefit) provision for income taxes	(5,889)	(9,073)
Net loss	(12,631)	(21,393)
Other comprehensive loss	(16,746)	6,051
Comprehensive loss	(29,377)	(15,342)
Reportable Legal Entities \| Guarantor Subsidiaries
Revenues:
Service revenues	481,483	443,305
Product revenues	121,582	116,650
Total revenues	603,065	559,955
Cost of revenues: (exclusive of items shown separately below)
Service cost of revenues	328,180	294,145
Product cost of revenues	95,038	96,505
Total cost of revenues	423,218	390,650
Selling, general and administrative expenses	93,843	92,171
Accretion of environmental liabilities	2,176	2,055
Depreciation and amortization	53,704	51,900
Income from operations	30,124	23,179
Other expense, net	(85)	(1,389)
Interest (expense) income, net	505	119
Equity in earnings of subsidiaries, net of taxes	(20,062)	(21,824)
Intercompany interest income (expense)	1,361	1,297
(Loss) income before (benefit) provision for income taxes	11,843	1,382
(Benefit) provision for income taxes	9,101	9,637
Net loss	2,742	(8,255)
Other comprehensive loss	(16,746)	6,051
Comprehensive loss	(14,004)	(2,204)
Reportable Legal Entities \| Non-Guarantor Subsidiaries
Revenues:
Service revenues	152,401	131,071
Product revenues	11,450	15,331
Total revenues	163,851	146,402
Cost of revenues: (exclusive of items shown separately below)
Service cost of revenues	133,634	111,104
Product cost of revenues	6,711	12,247
Total cost of revenues	140,345	123,351
Selling, general and administrative expenses	21,210	20,026
Accretion of environmental liabilities	254	235
Depreciation and amortization	21,140	20,512
Income from operations	(19,098)	(17,722)
Other expense, net	(214)	(14)
Interest (expense) income, net	224	(36)
Equity in earnings of subsidiaries, net of taxes	0	0
Intercompany interest income (expense)	(1,361)	(1,297)
(Loss) income before (benefit) provision for income taxes	(20,449)	(19,069)
(Benefit) provision for income taxes	(159)	2,137
Net loss	(20,290)	(21,206)
Other comprehensive loss	(14,007)	5,032
Comprehensive loss	(34,297)	(16,174)
Consolidating Adjustments
Revenues:
Service revenues	(14,165)	(14,162)
Product revenues	(2,973)	(3,254)
Total revenues	(17,138)	(17,416)
Cost of revenues: (exclusive of items shown separately below)
Service cost of revenues	(14,165)	(14,162)
Product cost of revenues	(2,973)	(3,254)
Total cost of revenues	(17,138)	(17,416)
Selling, general and administrative expenses	0	0
Accretion of environmental liabilities	0	0
Depreciation and amortization	0	0
Income from operations	0	0
Other expense, net	0	0
Interest (expense) income, net	0	0
Equity in earnings of subsidiaries, net of taxes	17,548	29,461
Intercompany interest income (expense)	0	0
(Loss) income before (benefit) provision for income taxes	17,548	29,461
(Benefit) provision for income taxes	0	0
Net loss	17,548	29,461
Other comprehensive loss	30,753	(11,083)
Comprehensive loss	$ 48,301	$ 18,378

GUARANTOR AND NON-GUARANTOR SUBSIDIARIES FINANCIAL INFORMATION (Condensed Consolidating Statements of Cash Flows) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Condensed consolidating statement of cash flows
Net cash from (used in) operating activities	$ 51,903	$ 57,119
Cash flows used in investing activities:
Additions to property, plant and equipment	(44,242)	(42,462)
Proceeds from sale and disposal of fixed assets	798	1,030
Acquisitions, net of cash acquired	(120,000)	(11,946)
Proceeds from sale of business	0	2,018
Additions to intangible assets, including costs to obtain or renew permits	(1,245)	(751)
Proceeds from sale of available-for-sale securities	3,264
Purchases of available-for-sale securities	(3,003)	0
Proceeds from sale of investments		243
Intercompany	0	0
Net cash used in investing activities	(164,428)	(51,868)
Cash flows used in financing activities:
Change in uncashed checks	(3,843)	(7,557)
Proceeds from exercise of stock options	0	46
Tax payments related to withholdings on vested restricted stock	(548)	(1,021)
Repurchases of common stock	(14,264)	(6,796)
Deferred financing costs paid	0	(108)
Principal payment on debt	(1,000)	0
Intercompany	0	0
Net cash used in financing activities	(19,655)	(15,436)
Effect of exchange rate change on cash	(867)	554
Increase (decrease) in cash and cash equivalents	(133,047)	(9,631)
Cash and cash equivalents, beginning of period	319,399	306,997
Cash and cash equivalents, end of period	186,352	297,366
Consolidating Adjustments
Condensed consolidating statement of cash flows
Net cash from (used in) operating activities	0	0
Cash flows used in investing activities:
Additions to property, plant and equipment	0	0
Proceeds from sale and disposal of fixed assets	0	0
Acquisitions, net of cash acquired	0	0
Proceeds from sale of business		0
Additions to intangible assets, including costs to obtain or renew permits	0	0
Proceeds from sale of available-for-sale securities	0
Purchases of available-for-sale securities	0
Proceeds from sale of investments		0
Intercompany	15,812	7,771
Net cash used in investing activities	15,812	7,771
Cash flows used in financing activities:
Change in uncashed checks	0	0
Proceeds from exercise of stock options		0
Tax payments related to withholdings on vested restricted stock	0	0
Repurchases of common stock	0	0
Deferred financing costs paid		0
Principal payment on debt	0
Intercompany	(15,812)	(7,771)
Net cash used in financing activities	(15,812)	(7,771)
Effect of exchange rate change on cash	0	0
Increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents, beginning of period	0	0
Cash and cash equivalents, end of period	0	0
Clean Harbors, Inc.
Cash flows used in investing activities:
Proceeds from sale of investments		243
Clean Harbors, Inc. \| Reportable Legal Entities
Condensed consolidating statement of cash flows
Net cash from (used in) operating activities	143	(1,663)
Cash flows used in investing activities:
Additions to property, plant and equipment	0	0
Proceeds from sale and disposal of fixed assets	0	0
Acquisitions, net of cash acquired	0	0
Proceeds from sale of business		1,837
Additions to intangible assets, including costs to obtain or renew permits	0	0
Proceeds from sale of available-for-sale securities	0
Purchases of available-for-sale securities	0
Intercompany	0	0
Net cash used in investing activities	0	2,080
Cash flows used in financing activities:
Change in uncashed checks	0	0
Proceeds from exercise of stock options		46
Tax payments related to withholdings on vested restricted stock	(548)	(1,021)
Repurchases of common stock	(14,264)	(6,796)
Deferred financing costs paid		(108)
Principal payment on debt	(1,000)
Intercompany	15,812	7,771
Net cash used in financing activities	0	(108)
Effect of exchange rate change on cash	0	0
Increase (decrease) in cash and cash equivalents	143	309
Cash and cash equivalents, beginning of period	51,638	51,417
Cash and cash equivalents, end of period	51,781	51,726
Guarantor Subsidiaries
Cash flows used in investing activities:
Proceeds from sale of investments		0
Guarantor Subsidiaries \| Reportable Legal Entities
Condensed consolidating statement of cash flows
Net cash from (used in) operating activities	69,536	41,144
Cash flows used in investing activities:
Additions to property, plant and equipment	(37,319)	(33,136)
Proceeds from sale and disposal of fixed assets	292	664
Acquisitions, net of cash acquired	(120,000)	(11,946)
Proceeds from sale of business		0
Additions to intangible assets, including costs to obtain or renew permits	(1,234)	(573)
Proceeds from sale of available-for-sale securities	0
Purchases of available-for-sale securities	0
Intercompany	(15,812)	(7,771)
Net cash used in investing activities	(174,073)	(52,762)
Cash flows used in financing activities:
Change in uncashed checks	(3,578)	(5,165)
Proceeds from exercise of stock options		0
Tax payments related to withholdings on vested restricted stock	0	0
Repurchases of common stock	0	0
Deferred financing costs paid		0
Principal payment on debt	0
Intercompany	0	0
Net cash used in financing activities	(3,578)	(5,165)
Effect of exchange rate change on cash	0	0
Increase (decrease) in cash and cash equivalents	(108,115)	(16,783)
Cash and cash equivalents, beginning of period	207,777	155,943
Cash and cash equivalents, end of period	99,662	139,160
Non-Guarantor Subsidiaries
Cash flows used in investing activities:
Proceeds from sale of investments		0
Non-Guarantor Subsidiaries \| Reportable Legal Entities
Condensed consolidating statement of cash flows
Net cash from (used in) operating activities	(17,776)	17,638
Cash flows used in investing activities:
Additions to property, plant and equipment	(6,923)	(9,326)
Proceeds from sale and disposal of fixed assets	506	366
Acquisitions, net of cash acquired	0	0
Proceeds from sale of business		181
Additions to intangible assets, including costs to obtain or renew permits	(11)	(178)
Proceeds from sale of available-for-sale securities	3,264
Purchases of available-for-sale securities	(3,003)
Intercompany	0	0
Net cash used in investing activities	(6,167)	(8,957)
Cash flows used in financing activities:
Change in uncashed checks	(265)	(2,392)
Proceeds from exercise of stock options		0
Tax payments related to withholdings on vested restricted stock	0	0
Repurchases of common stock	0	0
Deferred financing costs paid		0
Principal payment on debt	0
Intercompany	0	0
Net cash used in financing activities	(265)	(2,392)
Effect of exchange rate change on cash	(867)	554
Increase (decrease) in cash and cash equivalents	(25,075)	6,843
Cash and cash equivalents, beginning of period	59,984	99,637
Cash and cash equivalents, end of period	$ 34,909	$ 106,480

UNAUDITED CONSOLIDATED STATEMENTS OF OPERATIONS (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Interest expense	$ 764	$ 215

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

GUARANTOR AND NON-GUARANTOR SUBSIDIARIES FINANCIAL INFORMATION (Narrative) (Details)	3 Months Ended
	Mar. 31, 2018
Guarantor and Non-Guarantor Subsidiaries Financial Information [Abstract]
Ownership percentage of U.S. guarantor subsidiaries	100.00%