Clean Harbors (CLH) 10-K 28 Feb 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2017	Feb. 23, 2018	Jun. 30, 2017
Document and Entity Information [Abstract]
Entity Registrant Name	CLEAN HARBORS INC
Entity Central Index Key	822,818
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		56,506,765
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 2.9

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 319,399	$ 306,997
Short-term marketable securities	38,179	0
Accounts receivable, net of allowances aggregating $27,799 and $29,249, respectively	528,924	496,226
Unbilled accounts receivable	35,922	36,190
Deferred costs	20,445	18,914
Inventories and supplies	176,012	178,428
Prepaid expenses and other current assets	35,175	56,116
Total current assets	1,154,056	1,092,871
Property, plant and equipment, net	1,587,365	1,611,827
Other assets:
Goodwill	478,523	465,154
Permits and other intangibles, net	469,128	498,721
Other	17,498	13,347
Total other assets	965,149	977,222
Total assets	3,706,570	3,681,920
Current liabilities:
Current portion of long-term obligations	4,000	0
Accounts payable	224,231	229,534
Deferred revenue	67,822	64,397
Accrued expenses	187,982	190,721
Current portion of closure, post-closure and remedial liabilities	19,782	20,016
Total current liabilities	503,817	504,668
Other liabilities:
Closure and post-closure liabilities, less current portion of $6,444 and $6,220, respectively	54,593	52,111
Remedial liabilities, less current portion of $13,338 and $13,796, respectively	111,130	114,211
Long-term obligations, less current portion	1,625,537	1,633,272
Deferred taxes, unrecognized tax benefits and other long-term liabilities	223,291	293,417
Total other liabilities	2,014,551	2,093,011
Commitments and contingent liabilities (See Note 17)
Stockholders' equity:
Common stock, $.01 par value: Authorized 80,000,000 shares; issued and outstanding 56,501,190 and 57,297,978 shares, respectively	565	573
Shares held under employee participation plan	0	(469)
Additional paid-in capital	686,962	725,670
Accumulated other comprehensive loss	(172,407)	(214,326)
Accumulated earnings	673,082	572,793
Total stockholders' equity	1,188,202	1,084,241
Total liabilities and stockholders' equity	$ 3,706,570	$ 3,681,920

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Account receivable, allowances aggregating	$ 27,799	$ 29,249
Closure and post-closure liabilities, current portion	6,444	6,220
Remedial liabilities, current portion	$ 13,338	$ 13,796
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, authorized shares (in shares)	80,000,000	80,000,000
Common stock, issued shares (in shares)	56,501,190	57,297,978
Common stock, outstanding shares (in shares)	56,501,190	57,297,978

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues:
Service revenues									$ 2,398,650	$ 2,280,809	$ 2,744,272
Product revenues									546,328	474,417	530,865
Total revenues	$ 747,403	$ 755,846	$ 752,788	$ 688,941	$ 692,113	$ 729,520	$ 697,510	$ 636,083	2,944,978	2,755,226	3,275,137
Cost of revenues: (exclusive of items shown separately below)
Service revenues									1,641,798	1,543,210	1,898,907
Product revenues									420,875	389,647	457,899
Total cost of revenues	526,690	519,595	519,803	496,585	496,661	491,915	480,002	464,279	2,062,673	1,932,857	2,356,806
Selling, general and administrative expenses									456,648	422,015	414,164
Accretion of environmental liabilities									9,460	10,177	10,402
Depreciation and amortization									288,422	287,002	274,194
Goodwill impairment charges						34,000			0	34,013	31,992
Income (loss) from operations	27,935	47,663	46,744	5,433	21,943	16,802	34,504	(4,087)	127,775	69,162	187,579
Other (expense) income, net	(3,305)	(432)	(833)	(1,549)	6,932	(198)	(189)	(350)	(6,119)	6,195	(1,380)
Loss on early extinguishment of debt		(1,900)	(6,000)						(7,891)	0	0
Gain on sale of businesses			31,700			16,400			30,732	16,884	0
Interest expense, net of interest income of $1,897, $784, and $626, respectively									(85,808)	(83,525)	(76,553)
Income (loss) before (benefit) provision for income taxes									58,689	8,716	109,646
(Benefit) provision for income taxes									(42,050)	48,589	65,544
Net income (loss)	$ 84,194	$ 12,058	$ 25,880	$ (21,393)	$ (12,713)	$ (10,255)	$ 3,966	$ (20,871)	$ 100,739	$ (39,873)	$ 44,102
Earnings (loss) per share:
Basic (in dollars per share)	$ 1.48	$ 0.21	$ 0.45	$ (0.37)	$ (0.22)	$ (0.18)	$ 0.07	$ (0.36)	$ 1.77	$ (0.69)	$ 0.76
Diluted (in dollars per share)	$ 1.48	$ 0.21	$ 0.45	$ (0.37)	$ (0.22)	$ (0.18)	$ 0.07	$ (0.36)	$ 1.76	$ (0.69)	$ 0.76
Shares used to compute earnings (loss) per share — Basic (in shares)									57,072	57,532	58,324
Shares used to compute earnings (loss) per share — Diluted (in shares)									57,200	57,532	58,434

CONSOLIDATED STATEMENTS OF OPE5

CONSOLIDATED STATEMENTS OF OPERATIONS (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Interest expense, interest income	$ 1,897	$ 784	$ 626

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net (loss) income	$ 100,739	$ (39,873)	$ 44,102
Other comprehensive income (loss):
Unrealized gains (losses) on available-for-sale securities (net of taxes of $152, ($214) and $0, respectively)	32	(321)	0
Reclassification adjustment for losses on available-for-sale securities included in net income (net of taxes of $79, $0, $0, respectively)	143	0	0
Foreign currency translation adjustments (including a tax benefit of $16.8 million in 2016)	41,636	40,728	(144,050)
Unfunded pension liability (net of taxes of $38, $57 and $7, respectively)	108	159	0
Other comprehensive income (loss)	41,919	40,566	(144,050)
Comprehensive income (loss)	$ 142,658	$ 693	$ (99,948)

CONSOLIDATED STATEMENTS OF COM7

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Unrealized gains on available-for-sale securities, taxes	$ (152)	$ 214	$ 0
Reclassification adjustment for gains on available-for-sale securities included in net income, taxes	79	0	0
Foreign current translation adjustments, tax benefit	0	16,800	0
Unfunded pension liability, taxes	$ 38	$ 57	$ 7

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net (loss) income	$ 100,739	$ (39,873)	$ 44,102
Adjustments to reconcile net income (loss) to net cash from operating activities:
Depreciation and amortization	288,422	287,002	274,194
Goodwill impairment charges	0	34,013	31,992
Allowance for doubtful accounts	7,901	6,907	4,793
Amortization of deferred financing costs and debt discount	3,482	3,537	3,280
Accretion of environmental liabilities	9,460	10,177	10,402
Changes in environmental liability estimates	(195)	(4,254)	(11,345)
Deferred income taxes	(83,335)	15,184	1,930
Other expense (income), net	6,119	(5,685)	1,380
Stock-based compensation	13,146	10,481	8,550
Excess tax benefit of stock-based compensation	0	(1,198)	(71)
Net tax benefit (deficiency) on stock-based awards	0	1,165	(82)
Gain on sale of businesses	(30,732)	(16,884)	0
Loss on early extinguishment of debt	7,891	0	0
Environmental expenditures	(12,965)	(12,170)	(20,130)
Changes in assets and liabilities, net of acquisitions:
Accounts receivable and unbilled accounts receivable	(33,764)	(15,009)	55,271
Inventories and supplies	(5,002)	(16,080)	14,059
Other current assets	16,720	(8,036)	48,760
Accounts payable	(10,684)	(3,503)	(16,299)
Other current and long-term liabilities	8,495	13,850	(54,403)
Net cash from operating activities	285,698	259,624	396,383
Cash flows used in investing activities:
Additions to property, plant and equipment	(167,007)	(219,384)	(257,196)
Proceeds from sale and disposal of fixed assets	7,124	20,817	6,195
Acquisitions, net of cash acquired	(49,227)	(206,915)	(94,345)
Additions to intangible assets including costs to obtain or renew permits	(1,617)	(2,831)	(5,296)
Purchases of available-for-sale securities	(38,342)	(598)	0
Proceeds on sale of businesses, net of transactional costs	45,426	47,134	0
Proceeds from sale of long-term investments	376	0	0
Net cash used in investing activities	(203,267)	(361,777)	(350,642)
Cash flows (used in) from financing activities:
Change in uncashed checks	(5,940)	(3,177)	(14,630)
Proceeds from exercise of stock options	46	627	397
Tax payments related to withholdings on vested restricted stock	(3,149)	(2,819)	(2,159)
Repurchases of common stock	(48,971)	(22,188)	(73,347)
Excess tax benefit of stock-based compensation	0	1,198	71
Deferred financing costs paid	(5,718)	(4,031)	0
Payments on capital leases	0	0	(511)
Premiums paid on early extinguishment of debt	(6,028)	0	0
Principal payment on debt	(402,000)	0	0
Issuance of senior secured notes, net of discount	399,000	0	0
Issuance of senior unsecured notes, including premium	0	250,625	0
Net cash (used in) from financing activities	(72,760)	220,235	(90,179)
Effect of exchange rate change on cash	2,731	4,207	(17,733)
Increase (decrease) in cash and cash equivalents	12,402	122,289	(62,171)
Cash and cash equivalents, beginning of year	306,997	184,708	246,879
Cash and cash equivalents, end of year	319,399	306,997	184,708
Cash payments for interest and income taxes:
Interest paid	93,174	88,669	73,926
Income taxes paid	18,682	29,255	52,970
Non-cash investing activities:
Property, plant and equipment accrued	16,109	9,214	32,677
Transfer of inventory to property, plant and equipment	12,641	0	0
Receivable for estimated purchase price adjustment	$ 0	$ 1,910	$ 1,000

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Shares Held Under Employee Participation Plan	Additional Paid-in Capital	Accumulated Other Comprehensive loss	Accumulated Earnings
Beginning balance at Dec. 31, 2014	$ 1,262,871	$ 589	$ (469)	$ 805,029	$ (110,842)	$ 568,564
Beginning balance (in shares) at Dec. 31, 2014		58,903
Increase (Decrease) in Stockholders' Equity
Net (loss) income	44,102					44,102
Other comprehensive loss	(144,050)				(144,050)
Stock-based compensation	8,550			8,550
Issuance of restricted shares, net of shares remitted	(2,159)	$ 1		(2,160)
Issuance of restricted shares, net of shares remitted (in shares)		100
Exercise of stock options	397			397
Exercise of stock options (in shares)		12
Repurchases of common stock	(73,347)	$ (14)		(73,333)
Repurchases of common stock (in shares)		(1,422)
Net tax benefit on stock-based awards	(82)			(82)
Ending balance at Dec. 31, 2015	1,096,282	$ 576	(469)	738,401	(254,892)	612,666
Ending balance (in shares) at Dec. 31, 2015		57,593
Increase (Decrease) in Stockholders' Equity
Net (loss) income	(39,873)					(39,873)
Other comprehensive loss	40,566				40,566
Stock-based compensation	10,481			10,481
Issuance of restricted shares, net of shares remitted	(2,819)	$ 1		(2,820)
Issuance of restricted shares, net of shares remitted (in shares)		136
Exercise of stock options	627			627
Exercise of stock options (in shares)		22
Repurchases of common stock	(22,188)	$ (4)		(22,184)
Repurchases of common stock (in shares)		(453)
Net tax benefit on stock-based awards	1,165			1,165
Ending balance at Dec. 31, 2016	1,084,241	$ 573	(469)	725,670	(214,326)	572,793
Ending balance (in shares) at Dec. 31, 2016		57,298
Increase (Decrease) in Stockholders' Equity
Net (loss) income	100,739					100,739
Other comprehensive loss	41,919				41,919
Stock-based compensation	13,146			13,146
Issuance of restricted shares, net of shares remitted	(3,149)	$ 1		(3,150)
Issuance of restricted shares, net of shares remitted (in shares)		133
Exercise of stock options	46			46
Shares held under employee participation plan	0		469	(469)
Shares held under employee participation plan (in shares)		(25)
Exercise of stock options (in shares)		2
Repurchases of common stock	(48,971)	$ (9)		(48,962)
Repurchases of common stock (in shares)		(907)
Ending balance at Dec. 31, 2017	1,188,202	$ 565	$ 0	686,962	$ (172,407)	673,082
Ending balance (in shares) at Dec. 31, 2017		56,501
Increase (Decrease) in Stockholders' Equity
Cumulative effect of change in accounting for stock-based compensation	$ 231			$ 681		$ (450)

CONSOLIDATED STATEMENTS OF ST10

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (PARENTHETICAL) - $ / shares	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Stockholders' Equity [Abstract]
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01	$ 0.01

OPERATIONS

OPERATIONS	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Operations	OPERATIONS Clean Harbors, Inc., through its subsidiaries (collectively, the "Company"), is a leading provider of environmental, energy and industrial services throughout North America.

SIGNIFICANT ACCOUNTING POLICIES

SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
SIGNIFICANT ACCOUNTING POLICIES	SIGNIFICANT ACCOUNTING POLICIES The accompanying consolidated financial statements of the Company reflect the application of certain significant accounting policies as described below: Principles of Consolidation The accompanying consolidated statements include the accounts of Clean Harbors, Inc. and its majority-owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation. Use of Estimates The preparation of consolidated financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions, which are evaluated on an ongoing basis, that affect the amounts reported in the Company's consolidated financial statements and accompanying notes. Management bases its estimates on historical experience and on various other assumptions it believes to be reasonable at the time under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities and disclosure, if any, of contingent assets and liabilities and reported amounts of revenues and expenses. Actual results could differ from those estimates and judgments. Cash and Uncashed Checks Cash consists primarily of cash on deposit and money market accounts. The Company's cash management program with its revolving credit lender allows for the maintenance of a zero balance in the U.S. bank disbursement accounts that are used to issue vendor and payroll checks. The program can result in checks outstanding in excess of bank balances in the disbursement accounts. When checks are presented to the bank for payment, cash deposits in amounts sufficient to fund the checks are made, at the Company's discretion, either from funds provided by other accounts or under the terms of the Company's revolving credit facility. Therefore, until checks are presented for payment, there is no right of offset by the bank and the Company continues to have control over cash relating to both released as well as unreleased checks. Checks that have been written to vendors or employees but have not yet been presented for payment at the Company's bank are classified as uncashed checks as part of accounts payable. Marketable Securities Marketable securities with maturities of three months or less from the date of purchase are classified as cash equivalents. Marketable securities with original maturities greater than three months from purchase date and remaining maturities less than one year are classified as short-term marketable securities. Marketable securities with remaining maturities greater than one year as of the balance sheet date and which the Company intends to hold for greater than one year, are classified as long-term marketable securities. The Company has classified its marketable securities as available-for-sale and, accordingly, carries such securities at fair value. Unrealized gains and losses are reported, net of tax, as a component of other comprehensive income (loss). (2) SIGNIFICANT ACCOUNTING POLICIES (Continued) Available-for-sale investments were as follows (in thousands): December 31, 2017 Amortized Cost Gross Unrealized Loss Gross Unrealized Gain Fair Value Commercial paper $ 2,048 $ — $ — $ 2,048 Total cash equivalents 2,048 — — 2,048 U.S. Treasury securities 3,865 (10 ) — 3,855 Corporate notes and bonds 32,790 (61 ) — 32,729 Commercial paper 1,595 — — 1,595 Total short-term marketable securities 38,250 (71 ) — 38,179 Total financial assets $ 40,298 $ (71 ) $ — $ 40,227 The gross unrealized loss related to these securities was due primarily to changes in interest rates and was considered temporary in nature. Realized gains and losses on sales of available-for-sale securities in the year ended December 31, 2017 were immaterial. Marketable securities by contractual maturity as of December 31, 2017 are shown below (in thousands). Amortized Cost Fair Value Due in one year or less $ 18,684 $ 18,670 After one year through three years 21,614 21,557 Total financial assets $ 40,298 $ 40,227 Fair Value Measurements The Company defines fair value as the price that would be received to sell an asset or be paid to transfer a liability in an orderly transaction between market participants at the measurement date. The Company applies the following fair value hierarchy, which prioritizes the inputs used to measure fair value into three levels and bases the categorization within the hierarchy upon the lowest level of input that is available and significant to the fair value measurement. Level 1 inputs are quoted prices in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date. Level 2 utilizes quoted market prices in markets that are not active, broker or dealer quotations, or alternative pricing sources with reasonable levels of price transparency. Level 3 inputs are unobservable inputs for the asset or liability in which there is little, if any, market activity for the asset or liability at the measurement date. The Company's financial instruments consist of cash, marketable securities, accounts and unbilled receivable, accounts payable, accrued liabilities and long-term debt obligations. Due to the short-term nature of these instruments, with the exception of long-term debt obligations and marketable securities, their estimated fair value approximates carrying value. Senior unsecured notes are recorded at par. (2) SIGNIFICANT ACCOUNTING POLICIES (Continued) Financial assets measured and recorded at fair value on a recurring basis consisted of the following types of instruments (in thousands): December 31, 2017 Level 1 Level 2 Level 3 Total Commercial paper $ — $ 2,048 $ — $ 2,048 Total cash equivalents — 2,048 — 2,048 U.S. Treasury securities 3,855 — — 3,855 Corporate notes and bonds — 32,729 — 32,729 Commercial paper — 1,595 — 1,595 Total short-term marketable securities 3,855 34,324 — 38,179 Total financial assets $ 3,855 $ 36,372 $ — $ 40,227 The Company’s Level 2 securities are primarily valued using quoted market prices for similar instruments and non-binding market prices that are corroborated by observable market data. The Company uses inputs such as actual trade data, benchmark yields, broker/dealer quotes and other similar data, which are obtained from independent pricing vendors, to determine the ultimate fair value of the Company’s assets and liabilities. The inputs and fair value are reviewed for reasonableness. During the year ended December 31, 2017, the Company had no transfers of financial assets and liabilities between Level 1 and Level 2. As of December 31, 2017, the Company had not elected the fair value option for any financial assets and liabilities for which such an election would have been permitted. Allowances for Doubtful Accounts On a regular basis, the Company evaluates its accounts receivable and establishes the allowance for doubtful accounts based on an evaluation of certain criteria and evidence of collection certainty including historical collection trends, current economic trends and changes in customer payment patterns. Past-due receivable balances are written off when the Company's internal collection efforts have been deemed unsuccessful in collecting the outstanding balance due. Credit Concentration Concentration of credit risks in accounts receivable is limited due to the large number of customers comprising the Company's customer base throughout North America. The Company maintains policies over credit extension that include credit evaluations, credit limits and collection monitoring procedures on a customer-by-customer basis. However, the Company generally does not require collateral before services are performed. As of December 31, 2017 and 2016 , no individual customer accounted for more than 10% of accounts receivable. During each of the years ended December 31, 2017 , 2016 and 2015 , no individual customer accounted for more than 10% of total revenues. Unbilled Receivables The Company recognizes unbilled accounts receivable for service and disposal transactions rendered but not invoiced to the customer as of the end of the period. Deferred Costs Commissions and other incremental direct costs, primarily costs of materials and transportation costs, relating to deferred revenue from the Company’s parts cleaning and waste services are capitalized and deferred. The deferred costs are included in current assets in the consolidated balance sheet and charged to expense when the related revenues are recognized. Inventories and Supplies Inventories are stated at the lower of cost or market. The cost of oil and oil products is principally determined on a first-in, first-out ("FIFO") basis. The cost of supplies and drums, solvent and solution and other inventories is determined on a FIFO or a weighted average cost basis. Costs for oil and oil products, solvent and repair parts include purchase costs, fleet and fuel (2) SIGNIFICANT ACCOUNTING POLICIES (Continued) costs, direct labor, transportation costs and production related costs. The Company continually reviews its inventories for obsolete or unsalable items and adjusts its carrying value to reflect estimated realizable values. Prepaid Expenses and Other Current Assets Prepaid expenses and other current assets consist primarily of prepayments for various services, refundable deposits, and income taxes receivable. Property, Plant and Equipment (excluding landfill assets) Property, plant and equipment are stated at cost and include amounts capitalized under capital lease obligations. Expenditures for major renewals and improvements which extend the life or usefulness of the asset are capitalized. Items of an ordinary repair or maintenance nature are charged directly to operating expense as incurred. During the construction and development period of an asset, the costs incurred, including applicable interest costs, are classified as construction-in-progress. The Company depreciates and amortizes the cost of these assets, using the straight-line method as follows: Asset Classification Estimated Useful Life Buildings and building improvements Buildings 30–42 years Leasehold and building improvements 2–45 years Camp equipment 8–15 years Vehicles 3–15 years Equipment Capitalized software and computer equipment 3–5 years Solar equipment 30 years Containers and railcars 15–20 years All other equipment 8–25 years Furniture and fixtures 5–8 years Leasehold and building improvements have a weighted average life of 9.6 years. Camp equipment consists of industrial lodging facilities that are utilized to provide lodging services to downstream oil and gas companies in Western Canada. Solar equipment consists of a solar array that is used to provide electric power for a continuously operating groundwater decontamination pump and treatment system at a closed and capped landfill located in New Jersey. The Company recognizes an impairment in the carrying value of long-lived assets when the expected future undiscounted cash flows derived from the assets, or group of assets, are less than their carrying value. For the years ended December 31, 2017 , 2016 and 2015 , the Company did not record impairment charges related to long-lived assets. The Company will continue to assess all of its long-lived assets for impairment as necessary. Goodwill Goodwill is comprised of the purchase price of business acquisitions in excess of the fair value assigned at acquisition to the net tangible and identifiable intangible assets acquired. Goodwill is not amortized but is reviewed for impairment annually as of December 31, or when events or changes in the business environment indicate that the carrying value of the reporting unit may exceed its fair value, by comparing the fair value of each reporting unit to its carrying value, including goodwill. Upon adoption of Accounting Standards Update (“ASU”) 2017-04 in the fourth quarter of 2017, if the fair value is less than the carrying amount, a loss will be recorded for the excess of the carrying value of the goodwill over the implied value of the goodwill. Prior to adoption of ASU 2017-04, if the fair value was less than the carrying amount, a Step II goodwill impairment test was performed to determine if goodwill was impaired. The loss, if any, was measured as the excess of the carrying value of the goodwill over the implied value of the goodwill. See Note 7, "Goodwill and Other Intangible Assets," for additional (2) SIGNIFICANT ACCOUNTING POLICIES (Continued) information related to the Company's goodwill impairment tests and the goodwill impairment charges recorded in 2016 and 2015. Permits and other intangibles Permits and intangible assets, such as legal fees, site surveys, engineering costs and other expenditures are recorded at cost. Other intangible assets consist primarily of customer and supplier relationships, trademarks and trade names, and non-compete agreements. Permits relating to landfills are amortized on a units-of-consumption basis. All other permits are amortized over periods ranging from 5 to 30 years on a straight-line basis. Other intangible assets are amortized on a straight-line basis over their respective useful lives, which range from 2 to 20 years. Finite-lived intangible assets are reviewed for impairment whenever events or changes in circumstances indicate that their carrying value may not be entirely recoverable. When such factors and circumstances exist, management compares the projected undiscounted future cash flows associated with the related asset or group of assets over their estimated useful lives against their respective carrying amounts. The impairment loss, if any, is measured as the excess of the carrying amount over the fair value of the asset or group of assets. Indefinite-lived intangible assets are not amortized but are reviewed for impairment annually as of December 31, or when events or changes in the business environment indicate that the carrying value may be impaired. If the fair value of the asset is less than the carrying amount, the Company performs a quantitative test to determine the fair value. The impairment loss, if any, is measured as the excess of the carrying value of the asset over its fair value. The fair value of the indefinite-lived intangible assets exceeded their carrying values at December 31, 2017 and 2016 . Leases The Company leases rolling stock, rail cars, equipment, real estate and office equipment under operating leases. Certain real estate leases contain rent holidays and rent escalation clauses. Most of the Company's real estate lease agreements include renewal periods at the Company's option. For its operating leases, the Company recognizes rent holiday periods and scheduled rent increases on a straight-line basis over the lease term beginning with the date the Company takes possession of the leased assets. Landfill Accounting The Company amortizes landfill improvements and certain landfill-related permits over their estimated useful lives. The units-of-consumption method is used to amortize land, landfill cell construction, asset retirement costs and remaining landfill cells and sites. The Company also utilizes the units-of-consumption method to record closure and post-closure obligations for landfill cells and sites. Under the units-of-consumption method, the Company includes future estimated construction and asset retirement costs, as well as costs incurred to date, in the amortization base of the landfill assets. Additionally, where appropriate, as described below, the Company includes probable expansion airspace that has yet to be permitted in the calculation of the total remaining useful life of the landfill. If it is determined that expansion capacity should no longer be considered in calculating the recoverability of a landfill asset, the Company may be required to recognize an asset impairment or incur significantly higher amortization expense. If at any time the Company makes the decision to abandon the expansion effort, the capitalized costs related to the expansion effort are expensed immediately. Landfill assets —Landfill assets include the costs of landfill site acquisition, permits and cell construction incurred to date. These amounts are recorded at cost, which includes capitalized interest as applicable. Landfill assets, net of amortization, are combined with management's estimate of the costs required to complete construction of the landfill to determine the amount to be amortized over the remaining estimated useful economic life of a site. Amortization of landfill assets is recorded on a units-of-consumption basis, such that the landfill assets should be completely amortized at the date the landfill ceases accepting waste. Amortization totaled $9.5 million , $9.7 million and $11.2 million for the years ended December 31, 2017 , 2016 and 2015 , respectively. Changes in estimated costs to complete construction are applied prospectively to the amortization rate. Landfill capacity —Landfill capacity, which is the basis for the amortization of landfill assets and for the accrual of final closure and post-closure obligations, represents total permitted airspace plus unpermitted airspace that management believes is probable of ultimately being permitted based on established criteria. The Company applies the following criteria for evaluating the probability of obtaining a permit for future expansion airspace at existing sites, which provides management a basis to evaluate the likelihood of success of unpermitted expansions: (2) SIGNIFICANT ACCOUNTING POLICIES (Continued) • Personnel are actively working to obtain the permit or permit modifications (land use, state, provincial and federal) necessary for expansion of an existing landfill, and progress is being made on the project. • Management expects to submit the application within the next year and to receive all necessary approvals to accept waste within the next 5 years. • At the time the expansion is included in the Company's estimate of the landfill's useful economic life, it is probable that the required approvals will be received within the normal application and processing time periods for approvals in the jurisdiction in which the landfill is located. • The Company or other owner of the landfill has a legal right to use or obtain the right to use the land associated with the expansion plan. • There are no significant known political, technical, legal or business restrictions or issues that could impair the success of such expansion. • A financial feasibility analysis has been completed and the results demonstrate that the expansion will have a positive financial and operational impact such that management is committed to pursuing the expansion. • Additional airspace and related additional costs, including permitting, final closure and post-closure costs, have been estimated based on the conceptual design of the proposed expansion. As of December 31, 2017 , there were two unpermitted expansions at two locations included in the Company's landfill accounting model, which represented 18.4% of the Company's remaining airspace at that date. If actual expansion airspace is significantly different from the Company's estimate of expansion airspace, the amortization rates used for the units-of-consumption method would change, therefore impacting the Company's profitability. If the Company determines that there is less actual expansion airspace at a landfill, this would increase amortization expense recorded and decrease profitability, while if the Company determines a landfill has more actual expansion airspace, amortization expense would decrease and profitability would increase. As of December 31, 2017 , the Company had 11 active landfill sites (including the Company's two non-commercial landfills), which have estimated remaining lives (based on anticipated waste volumes and remaining highly probable airspace) as follows: Remaining Lives (Years) Remaining Highly Probable Airspace (cubic yards) (in thousands) Facility Name Location Permitted Unpermitted Total Altair Texas 3 438 — 438 Buttonwillow California 20 6,459 — 6,459 Deer Park Texas 5 198 — 198 Deer Trail Colorado 33 1,812 — 1,812 Grassy Mountain Utah 59 291 4,830 5,121 Kimball Nebraska 8 211 — 211 Lambton Ontario 53 4,882 — 4,882 Lone Mountain Oklahoma 24 4,402 — 4,402 Ryley Alberta 8 351 880 1,231 Sawyer North Dakota 84 3,627 — 3,627 Westmorland California 64 2,732 — 2,732 25,403 5,710 31,113 At December 31, 2017 and 2016 , the Company had no cubic yards of permitted, but not highly probable, airspace. (2) SIGNIFICANT ACCOUNTING POLICIES (Continued) The following table presents the remaining highly probable airspace from January 1, 2015 through December 31, 2017 (in thousands of cubic yards): 2017 2016 2015 Remaining capacity at January 1, 32,228 29,786 30,544 Addition of highly probable airspace, net — 3,464 516 Consumed (1,115 ) (1,022 ) (1,274 ) Remaining capacity at December 31, 31,113 32,228 29,786 Amortization of cell construction costs and accrual of cell closure obligations —Landfills are typically comprised of a number of cells, which are constructed within a defined acreage (or footprint). The cells are typically discrete units, which require both separate construction and separate capping and closure procedures. Cell construction costs are the costs required to excavate and construct the landfill cell. These costs are typically amortized on a units-of-consumption basis, such that they are completely amortized when the specific cell ceases accepting waste. In some instances, the Company has landfills that are engineered and constructed as "progressive trenches." In progressive trench landfills, a number of contiguous cells form a progressive trench. In those instances, the Company amortizes cell construction costs over the airspace within the entire trench, such that the cell construction costs will be fully amortized at the end of the trench useful life. The design and construction of a landfill does not create a landfill asset retirement obligation. Rather, the asset retirement obligation for cell closure (the cost associated with capping each cell) is incurred in relatively small increments as waste is placed in the landfill. Therefore, the cost required to construct the cell cap is capitalized as an asset retirement cost and a liability of an equal amount is established, based on the discounted cash flow associated with each capping event, as airspace is consumed. Spending for cell capping is reflected as environmental expenditures within operating activities in the statement of cash flows. Landfill final closure and post-closure liabilities —The balance of landfill final closure and post-closure liabilities at December 31, 2017 and 2016 was $32.4 million and $30.6 million , respectively. The Company has material financial commitments for the costs associated with requirements of the Environmental Protection Agency ("EPA") and the comparable regulatory agency in Canada for landfill final closure and post-closure activities. In the United States, the landfill final closure and post-closure requirements are established under the standards of the EPA, and are implemented and applied on a state-by-state basis. The Company develops estimates for the cost of these activities based on an evaluation of site-specific facts and circumstances, including the Company's interpretation of current regulatory requirements and proposed regulatory changes. Such estimates may change in the future due to various circumstances including, but not limited to, permit modifications, changes in legislation or regulations, technological changes and results of environmental studies. Final closure costs are the costs incurred after the site ceases to accept waste, but before the landfill is certified as closed by the applicable state regulatory agency. These costs generally include the costs required to cap the final cell of the landfill (if not included in cell closure), the costs required to dismantle certain structures for landfills and other landfill improvements, and regulation-mandated groundwater monitoring, and leachate management. Post-closure costs involve the maintenance and monitoring of a landfill site that has been certified closed by the applicable regulatory agency. These costs generally include groundwater monitoring and leachate management. Regulatory post-closure periods are generally 30 years after landfill closure. Final closure and post-closure obligations are accrued on a units-of-consumption basis, such that the present value of the final closure and post-closure obligations are fully accrued at the date the landfill discontinues accepting waste. Cell closure, final closure and post-closure costs (also referred to as "asset retirement obligations") are calculated by estimating the total obligation in current dollars, adjusted for inflation ( 1.02% during 2017 and 2016 ) and discounted at the Company's credit-adjusted risk-free interest rate ( 6.32% and 6.23% during 2017 and 2016 , respectively.) Non-Landfill Closure and Post-Closure Liabilities Non-landfill closure costs include costs required to dismantle and decontaminate certain structures and other costs incurred during the closure process. Post-closure costs, if required, include associated maintenance and monitoring costs as required by the closure permit. Post-closure periods are performance-based and are not generally specified in terms of years in the closure permit, but generally range from 10 to 30 years or more. (2) SIGNIFICANT ACCOUNTING POLICIES (Continued) The Company records its non-landfill closure and post-closure liability by: (i) estimating the current cost of closing a non-landfill facility and the post-closure care of that facility, if required, based upon the closure plan that the Company is required to follow under its operating permit, or in the event the facility operates with a permit that does not contain a closure plan, based upon legally enforceable closure commitments made by the Company to various governmental agencies; (ii) using probability scenarios as to when in the future operations may cease; (iii) inflating the current cost of closing the non-landfill facility on a probability weighted basis using the inflation rate to the time of closing under each probability scenario; and (iv) discounting the future value of each closing scenario back to the present using the credit-adjusted risk-free interest rate. Non-landfill closure and post-closure obligations arise when the Company commences operations. The balance of non-landfill closure and post-closure liabilities at December 31, 2017 and 2016 was $28.6 million and $27.7 million , respectively. The estimates for non-landfill closure and post-closure liabilities are inherently uncertain due to the possibility that permit and regulatory requirements will change in the future, impacting the estimation of total costs and the timing of the expenditures. Management reviews non-landfill closure and post-closure liabilities for changes to key assumptions that would impact the amount of the recorded liabilities. Changes that would prompt management to revise a liability estimate include changes in legal requirements that impact the Company's expected closure plan or scope of work, in the market price of a significant cost item, in the probability scenarios as to when future operations at a location might cease, or in the expected timing of the cost expenditures. Changes in estimates for non-landfill closure and post-closure events immediately impact the required liability and the value of the corresponding asset. If a change is made to a fully-consumed asset, the adjustment is charged immediately to expense. When a change in estimate relates to an asset that has not been fully consumed, the adjustment to the asset recognized in income prospectively as a component of amortization. Historically, material changes to non-landfill closure and post-closure estimates have been infrequent. Remedial Liabilities The balance of remedial liabilities at December 31, 2017 and 2016 was $124.5 million and $128.0 million , respectively. Remedial liabilities, including Superfund liabilities, include the costs of removal or containment of contaminated material, treatment of potentially contaminated groundwater and maintenance and monitoring costs necessary to comply with regulatory requirements. Most of the Company's remedial liabilities relate to the active and inactive hazardous waste treatment and disposal facilities which the Company acquired in the last 15 years and 35 Superfund sites owned by third parties for which the Company agreed to indemnify certain remedial liabilities owed or potentially owed to governmental entities by the sellers of certain assets (the "CSD assets") which the Company acquired in 2002. The Company performed extensive due diligence to estimate accurately the aggregate liability for remedial liabilities to which the Company became potentially liable as a result of the acquisitions. The Company's estimate of remedial liabilities involved an analysis of such factors as: (i) the nature and extent of environmental contamination (if any); (ii) the terms of applicable permits and agreements with regulatory authorities as to cleanup procedures and whether modifications to such permits and agreements will likely need to be negotiated; (iii) the cost of performing anticipated cleanup activities based upon current technology; and (iv) in the case of Superfund and other sites where other parties will also be responsible for a portion of the cleanup costs, the likely allocation of such costs and the ability of such other parties to pay their share. Remedial liabilities and on-going operations are reviewed quarterly and adjustments are made as necessary. The Company periodically evaluates potential remedial liabilities at sites that it owns or operates or to which the Company or the sellers of the CSD assets (or the respective predecessors of the Company or such sellers) transported or disposed of waste, including 129 Superfund sites as of December 31, 2017 . The Company periodically reviews and evaluates sites requiring remediation, including Superfund sites, giving consideration to the nature (i.e., owner, operator, arranger, transporter or generator) and the extent (i.e., amount and nature of waste hauled to the location, number of years of site operations or other relevant factors) of the Company's (or such sellers') alleged connection with the site, the extent (if any) to which the Company believes it may have an obligation to indemnify cleanup costs in connection with the site, the regulatory context surrounding the site, the accuracy and strength of evidence connecting the Company (or such sellers) to the location, the number, connection and financial ability of other named and unnamed potentially responsible parties ("PRPs") and the nature and estimated cost of the likely remedy. Where the Company concludes that it is probable that a liability has been incurred and an amount can be estimated, a provision is made, based upon management's judgment and prior experience, of such estimated liability. Remedial liabilities are inherently difficult to estimate. Estimating remedial liabilities requires that the existing environmental contamination be understood. There are risks that the actual quantities of contaminants differ from the results of the site investigation, and that contaminants exist that have not been identified by the site investigation. In addition, the amount (2) SIGNIFICANT ACCOUNTING POLICIES (Continued) of remedial liabilities recorded is dependent on the remedial method selected. There is a risk that funds will be expended on a remedial solution that is not successful, which could result in the additional incremental costs of an alternative solution. Such estimates, which are subject to change, are subsequently revised if and when additional or new information becomes available. Remedial liabilities are discounted only when the timing of the payments is determinable and the amounts are estimable. Management's experience has been that the timing of payments for remedial liabilities is not usually estimable, and therefore the amounts of remedial liabilities are not generally discounted. In the case of remedial liabilities assumed in connection with acquisitions, acquired liabilities are recorded at fair value as of the dates of the acquisitions calculated by inflating costs in current dollars using an estimate of future inflation rates as of the respective acquisition dates until the expected time of paymen

BUSINESS COMBINATIONS

BUSINESS COMBINATIONS	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
BUSINESS COMBINATIONS	BUSINESS COMBINATIONS 2017 Acquisitions On October 16, 2017, the Company acquired a division of a privately held company for approximately $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 Industrial and Field 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 approximately $2.1 million . The acquired company is included in the Safety-Kleen operating segment and offers machines having an integrated recycling process that provides unparalleled resource recovery and waste minimization benefits. In connection with this acquisition a preliminary goodwill amount of $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 supports the Company's growth in the daylighting and hydro excavation services markets. In addition to increasing the size of the Company's hydro vac fleet, Lonestar's network of locations provides the Company with direct access to key geographic markets in both the United States and Canada. The acquired company is included in the Industrial and Field Services segment. 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, and subject to customary post-closing adjustments. 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 operating segment. In connection with this acquisition a goodwill amount of $5.0 million was recognized. The combined amount of direct revenue from the acquisitions included in the Company's results of operations for the year ended December 31, 2017 was approximately $14.5 million . Pro forma comparative financial information on a comparative (3) BUSINESS COMBINATIONS (Continued) basis, as if these acquisitions had been completed on January 1, 2016, is not presented as the pro forma results would not be materially different from reported trends and operations. 2016 Acquisitions During 2016, the Company acquired seven businesses that complement the strategy to create a closed loop model as it relates to the sale of the Company's oil products. These acquisitions provided the Company with three additional oil re-refineries while also expanding its used motor oil collection network and providing greater blending and packaging capabilities. These acquisitions also provide the Company with greater access to customers in the West Coast region of the United States and additional locations with Part B permits. Operations of these acquisitions were primarily integrated into the Safety-Kleen operating segment with certain operations also integrated into the Technical Services and Industrial Services operating segments. The combined purchase price for the seven acquisitions was $204.8 million paid in cash and subject to customary post-closing adjustments. The combined amount of direct revenue from the acquisitions included in the Company's results of operations for the year ended December 31, 2016 was approximately $69.8 million . Upon acquisition, the acquired entities were immediately integrated into the Company's operating segments. Therefore it is impracticable to measure earnings attributable to the acquired businesses. During the year ended December 31, 2016 , the Company incurred acquisition-related costs of approximately $1.7 million in connection with the transactions which are included in selling, general and administrative expenses in the consolidated statements of operations. The allocation of the purchase price was based on estimates of the fair value of assets acquired and liabilities assumed as of the acquisition dates. The Company believes that such information provides a reasonable basis for estimating the fair values of assets acquired and liabilities assumed. The Company finalized the purchase accounting for the seven acquisitions in the second quarter of 2017. The components and preliminary allocation of the purchase price consist of the following amounts (in thousands): At Acquisition Dates As Reported Measurement Period Adjustments Final Allocation Accounts receivable $ 15,767 $ 475 $ 16,242 Inventories and supplies 12,515 173 12,688 Prepaid expenses and other current assets 777 (25 ) 752 Property, plant and equipment 143,025 891 143,916 Permits and other intangibles 28,856 — 28,856 Current liabilities (20,258 ) 353 (19,905 ) Closure and post-closure liabilities, less current portion (2,408 ) (596 ) (3,004 ) Remedial liabilities, less current portion (2,041 ) (504 ) (2,545 ) Deferred taxes, unrecognized tax benefits and other long-term liabilities (17,019 ) (3,200 ) (20,219 ) Total identifiable net assets 159,214 (2,433 ) 156,781 Goodwill 45,791 2,186 47,977 Total purchase price, net of cash acquired $ 205,005 $ (247 ) $ 204,758 The excess of the total purchase price, which includes the aggregate cash consideration paid in excess of the fair value of the tangible net assets and intangible assets acquired, was recorded as goodwill. The goodwill recognized is attributable to the expected operating synergies and growth potential that the Company expects to realize from these acquisitions. Goodwill generated from the acquisitions was not deductible for tax purposes. Pro forma revenue and earnings amounts on a combined basis as if these acquisitions had been completed on January 1, 2015 are not materially different than the consolidated financial statements of the Company since that date. 2015 Acquisitions Thermo Fluids Inc. On April 11, 2015 , the Company completed the acquisition of Heckmann Environmental Services, Inc. (“HES”) and Thermo Fluids Inc. (“TFI”), a wholly-owned subsidiary of HES. The acquisition was accomplished through a purchase by (3) BUSINESS COMBINATIONS (Continued) Safety-Kleen, Inc., a wholly-owned subsidiary of the Company, of all of the issued and outstanding shares of HES from Nuverra Environmental Solutions, Inc. HES is a holding company that does not conduct any operations. TFI provides environmental services, including used oil recycling, used oil filter recycling, antifreeze products, parts washers and solvent recycling, and industrial waste management services, including vacuum services, remediation, lab pack and hazardous waste management. The Company acquired TFI for a purchase price of $79.3 million . The acquisition was financed with cash on hand and expanded the Company’s environmental services customer base while also complimenting the Safety-Kleen network and presence in the western United States. The amount of revenue from TFI included in the Company's results of operations for the years ended December 31, 2016 and 2015 was $38.0 million and $33.8 million , respectively. Upon acquisition, TFI was immediately integrated into the Company's Safety-Kleen operating segment. Therefore it is impracticable to measure earnings attributable to TFI. The allocation of the purchase price was based on estimates of the fair value of assets acquired and liabilities assumed as of April 11, 2015 . The Company believes that such information provides a reasonable basis for estimating the fair values of assets acquired and liabilities assumed. The Company finalized the purchase accounting for the acquisition of TFI in the second quarter of 2016. Preliminary Allocations as reported at December 31, 2015 Measurement Period Adjustments Final Allocations Accounts Receivable $ 7,585 $ (284 ) $ 7,301 Inventories and supplies 1,791 — 1,791 Prepaid expenses and other current assets 665 — 665 Property, plant and equipment 28,862 (1,221 ) 27,641 Permits and other intangibles 18,100 — 18,100 Current liabilities (5,845 ) (39 ) (5,884 ) Closure and post-closure liabilities (1,676 ) (657 ) (2,333 ) Deferred taxes, unrecognized tax benefits and other long-term liabilities (10,030 ) 856 (9,174 ) Total identifiable net assets 39,452 (1,345 ) 38,107 Goodwill 39,134 2,095 41,229 Total $ 78,586 $ 750 $ 79,336 Other 2015 Acquisitions In December 2015, the Company acquired certain assets and assumed certain defined liabilities of a privately owned company for approximately $14.7 million in cash. That company specializes in the collection and recycling of used oil filters and was a service provider to the Safety-Kleen operating segment prior to the acquisition. The acquired company was integrated into the Safety-Kleen operating segment. In connection with this acquisition a goodwill amount of $7.4 million was recognized.

DISPOSITION OF BUSINESS

DISPOSITION OF BUSINESS	12 Months Ended
	Dec. 31, 2017
Discontinued Operations and Disposal Groups [Abstract]
DISPOSITION OF BUSINESS	DISPOSITION OF BUSINESSES 2017 Disposition On June 30, 2017, the Company completed the sale of its Transformer Services business, as part of its continuous focus on improving or divesting certain non-core operations. The Transformer Services business was a non-core business previously included within the Technical Services operating segment and was sold for approximately $45.5 million ( $43.4 million net of $2.1 million in transactional related costs) subject to customary post-closing adjustments. As a result of the sale, the Company recognized during the year ended December 31, 2017 , a pre-tax gain of $30.7 million which is included in gain on sale of business in the Company’s consolidated statement of operations. (4) DISPOSITION OF BUSINESSES (Continued) The following table presents the carrying amounts of the Company's Transformer Services business that was disposed of on June 30, 2017 (in thousands): June 30, 2017 Total current assets $ 7,241 Property, plant and equipment, net 8,773 Total other assets 1,681 Total assets divested $ 17,695 Total current liabilities 3,849 Total other liabilities 1,170 Total liabilities divested $ 5,019 Net carrying value divested $ 12,676 The Company evaluated the disposition and determined it did not meet the “major effect” criteria for classification as a discontinued operation largely due to the nature and size of the operations of the disposed entity. However, the Company determined that the disposition represented an individually significant component of the Company’s business. The following table presents income attributable to the Transformer Services business included in the Company's consolidated results of operations for each of the periods shown and through its disposition on June 30, 2017 (in thousands): For the years ended December 31, 2017 2016 2015 Income before (benefit) provision for income taxes $ 2,771 $ 4,187 $ 3,597 2016 Disposition On September 1, 2016, the Company completed the sale of its Catalyst Services business, which was a non-core business previously included within the Industrial Services operating segment, for approximately $50.6 million ( $49.2 million net of cash retained by the Catalyst Services business) subject to customary post-closing adjustments. As a result of the sale, the Company recognized during the year ended December 31, 2016, a pre-tax gain of $16.9 million which was included in gain on sale of business in the Company’s consolidated statement of operations. Inclusive within this gain was $1.6 million of transactional related costs. During the first quarter of 2017, the Company and the buyer of the Catalyst Services business agreed to final working capital amounts and as a result the Company received $2.0 million of final sale proceeds. The following table presents the carrying amounts of the Company's Catalyst Services business immediately preceding the disposition on September 1, 2016 (in thousands): September 1, 2016 Total current assets $ 19,019 Property, plant and equipment, net 11,154 Total other assets 6,500 Total assets divested $ 36,673 Total current liabilities 4,040 Total other liabilities 566 Total liabilities divested $ 4,606 Net carrying value divested $ 32,067 (4) DISPOSITION OF BUSINESSES (Continued) The Company evaluated the disposition and determined it did not meet the “major effect” criteria for classification as a discontinued operation largely due to the nature and size of the operations of the disposed of entity. However, the Company determined that the disposition did represent an individually significant component of its business. The following table presents income attributable to the Catalyst Services business included in the Company's consolidated results of operations for each of the periods shown and through its disposition on September 1, 2016 (in thousands): For the years ended December 31, 2016 2015 Income before (benefit) provision for income taxes $ 290 $ 2,520

INVENTORIES AND SUPPLIES

INVENTORIES AND SUPPLIES	12 Months Ended
	Dec. 31, 2017
Inventory Disclosure [Abstract]
INVENTORIES AND SUPPLIES	INVENTORIES AND SUPPLIES Inventories and supplies consisted of the following (in thousands): December 31, 2017 December 31, 2016 Oil and oil related products $ 58,142 $ 52,158 Supplies and drums 94,242 90,610 Solvent and solutions 9,167 8,566 Modular camp accommodations 1,826 15,255 Other 12,635 11,839 Total inventories and supplies $ 176,012 $ 178,428 As of December 31, 2017 and 2016 , other inventories consisted primarily of cleaning fluids, such as absorbents and wipers, 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. During the second quarter of 2017, $12.6 million of modular camp accommodations inventory was transferred to and included as camp equipment within the Company's property, plant and equipment amount as such assets will be utilized in the Company's ongoing camp and lodging operations.

PROPERTY, PLANT, AND EQUIPMENT

PROPERTY, PLANT, AND EQUIPMENT	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
PROPERTY, PLANT, AND EQUIPMENT	PROPERTY, PLANT AND EQUIPMENT Property, plant and equipment consisted of the following (in thousands): December 31, 2017 December 31, 2016 Land $ 121,658 $ 120,575 Asset retirement costs (non-landfill) 14,593 14,567 Landfill assets 144,539 139,708 Buildings and improvements 414,384 373,160 Camp equipment 170,012 152,740 Vehicles 617,959 541,022 Equipment 1,644,102 1,483,736 Furniture and fixtures 5,708 5,492 Construction in progress 57,618 146,904 3,190,573 2,977,904 Less - accumulated depreciation and amortization 1,603,208 1,366,077 Total property, plant and equipment, net $ 1,587,365 $ 1,611,827 Interest in the amount of $0.6 million , $5.5 million and $2.0 million was capitalized to fixed assets during the years ended December 31, 2017 , 2016 and 2015 , respectively. Depreciation expense, inclusive of landfill amortization was $251.4 million , $247.0 million and $234.0 million for the years ended December 31, 2017 , 2016 and 2015 , respectively.

GOODWILL AND OTHER INTANGIBLE A

GOODWILL AND OTHER INTANGIBLE ASSETS	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
GOODWILL AND OTHER INTANGIBLE ASSETS	GOODWILL AND OTHER INTANGIBLE ASSETS The changes in goodwill for the years ended December 31, 2017 and 2016 were as follows (in thousands): Technical Industrial Safety-Kleen Oil, Gas and Lodging Services Totals Balance at January 1, 2016 $ 49,267 $ 105,286 $ 266,344 $ 32,208 $ 453,105 Increase from current period acquisitions 12,572 6,953 26,266 — 45,791 Measurement period adjustments from prior period acquisitions — — 2,095 — 2,095 Decrease from disposition of business — (4,994 ) — — (4,994 ) Goodwill impairment charge — — — (34,013 ) (34,013 ) Foreign currency translation (723 ) 723 1,365 1,805 3,170 Balance at December 31, 2016 $ 61,116 $ 107,968 $ 296,070 $ — $ 465,154 Increase from current period acquisitions — 3,000 5,687 — 8,687 Measurement period adjustments from prior period acquisitions — — 2,186 — 2,186 Decrease from disposition of business (1,300 ) — — — (1,300 ) Foreign currency translation 317 1,285 2,194 — 3,796 Balance at December 31, 2017 $ 60,133 $ 112,253 $ 306,137 $ — $ 478,523 The Company assesses goodwill for impairment on an annual basis as of December 31, or at an interim date when events or changes in the business environment would more likely than not reduce the fair value of a reporting unit below its carrying value. The Company conducted its annual impairment test of goodwill for all of the Company's reporting units with remaining goodwill as of December 31, 2017 and determined that no adjustment to the carrying value of goodwill for any reporting unit was then necessary because the fair values of the reporting units exceeded their respective carrying values. The fair value of all reporting units was determined using an income approach based upon estimates of future discounted cash flows. The resulting estimates of fair value were validated through the consideration of other factors such as the fair value of comparable companies to the reporting units and a reconciliation of the sum of all estimated fair values of the reporting units to the Company’s overall market capitalization. In all cases, except for the Company's Industrial Services reporting unit, the estimated fair values of the reporting units significantly exceeded their carrying values. Significant judgments and unobservable inputs categorized as Level III in the fair value hierarchy are inherent in the impairment tests performed and include assumptions about the amount and timing of expected future cash flows, growth rates, and the determination of appropriate discount rates. The Company believes that the assumptions used in its annual and any interim date impairment tests are reasonable, but variations in any of the assumptions may result in different calculations of fair values and impairment charges. The impacts of any adverse business and market conditions which impact the overall performance of the Company's reporting units will continue to be monitored. If the Company's reporting units do not achieve the financial performance that the Company expects, it is possible that additional goodwill impairment charges may result. There can therefore be no assurance that future events will not result in an impairment of goodwill. At December 31, 2017, the total accumulated goodwill impairment charges was $ 189.4 million , of which $ 34.0 million was recorded during the year ended December 31, 2016 within the Lodging Services reporting unit, and $ 32.0 million was recorded during the year ended December 31, 2015 within the Oil and Gas Field Services reporting unit. During the quarter ended September 30, 2016, certain events and changes in circumstances arose which led management to conclude that the fair value of the Lodging Services reporting unit was more likely than not less than its carrying value, and therefore an interim goodwill impairment test was performed. The primary events and changes in circumstances which led to this conclusion were: (7) GOODWILL AND OTHER INTANGIBLE ASSETS (Continued) • Macroeconomic conditions for service companies operating in western Canada’s oil sands region deteriorated in 2016 primarily due to persistently low oil and gas prices. Persistently low prices have caused Lodging Services' primary customers to significantly reduce, defer, or cancel oil and gas projects that are in, or had been planned for, this region during periods of more robust commodity pricing. • Government regulatory delays related to oil and gas pipeline projects have reduced management’s confidence that these projects will move forward in a timely manner or in the form that had been originally contemplated by their planners. These projects represented a significant portion of Lodging Services' future growth in terms of the demand for temporary accommodations provided by the Lodging Services reporting unit. While some of these projects have made recent advancements towards successful government approval, the lack of meaningful progress to date does not provide enough positive evidence that a recovery will be significant enough to improve Lodging Services' current forecasted outlook. • There have been consecutive historical quarters where business results were significantly less than internal forecasts, and previous actual results, for the Lodging Services reporting unit. • During the quarter ended September 30, 2016, management’s near-term outlook was clarified in regards to the business’ projections and the impacts of large scale forest fires which took place in the Fort McMurray area of Alberta, Canada, where the Company has significant Lodging Services operations. • Due to the factors listed above, management significantly lowered its 2016 forecasts and long-range performance relative to the Lodging Services reporting unit. In performing Step I of the interim goodwill impairment test, the estimated fair value of the Lodging Services reporting unit was determined using an income approach with discounted cash flows which were compared to the reporting unit’s carrying value as of September 30, 2016. Based on the results of that evaluation, the carrying amount of the reporting unit, including $34.0 million of goodwill, exceeded Lodging Services' estimated fair value and as a result the Company performed Step II of the goodwill impairment test to determine the amount of goodwill impairment that would need to be recognized. Step II of the goodwill impairment test required the Company to perform a theoretical purchase price allocation for Lodging Services to determine the implied fair value of its goodwill and then compare that implied fair value to its recorded amount. Estimates and assumptions were used to determine the fair values for Lodging Services long-lived assets in Step II and these involved the use of significant professional judgment on the part of management. The classes of assets that were affected by these estimates and assumptions related most significantly to property, plant, and equipment, goodwill, and intangible assets. Based on the results of this test the implied fair value of goodwill was determined to be $0 . Accordingly, the Company recognized a goodwill impairment charge equal to its recorded amount, or $34.0 million , as of September 30, 2016. The factors contributing to the $34.0 million goodwill impairment charge principally related to events and changes in circumstances discussed above which negatively impacted the Company’s prospective financial information in its discounted cash flow model and the reporting unit's estimated fair value. Lower levels of pricing and an unfavorable change in product mix that reduced expected profit became evident during the quarter ended September 30, 2016 due to market conditions as management updated the Company's long-term projections for the business which, as a result, decreased the reporting unit’s anticipated future cash flows as compared to those estimated previously. These factors also provided evidence of a longer than expected recovery from current industry depressed pricing and activity levels, which negatively impacted the estimated levels of cash flows in future periods that are assumed in the cash flow model. These factors adversely affected the estimated fair value of the reporting unit and ultimately led to the recognition of the goodwill impairment charge. During the second quarter of 2015, certain events and changes in circumstances arose which led management of the Company to conclude that the fair value of the Oil and Gas Field Services reporting unit may be less than its carrying value and therefore an interim impairment test was conducted relative to goodwill recorded by the Oil and Gas Field Services reporting unit. The primary events and changes in circumstances which led to this conclusion were: • The second quarter is the period of time where greater levels of communication with customers and the receipt of bids and proposals for project work take place and provide management with more clarity into levels of activity and other economic and business indicators for the latter half of the fiscal year and into the first quarter of the following year. (7) GOODWILL AND OTHER INTANGIBLE ASSETS (Continued) • During the quarter ended June 30, 2015, it became apparent that oil and gas exploration and production activity would continue to be lower than prior periods and then previously anticipated by the Company. This was evidenced by reduced volume in bid and proposal requests from customers and communications indicating the reduction in customer budgets in these areas as well as lower than anticipated pricing for the Company's services. • Market and industry reports to which management looks in projecting business conditions and establishing forecast information evidenced more pessimistic views in the near term. The continued depressed price of oil without any upward momentum since December 2014, as well as declining and expected continued decline in rig count for the remainder of 2015, resulted in lower estimates of industry activity in the second half of 2015 and early 2016. • In recognition of lower than anticipated business results and less optimistic market indicators, management significantly lowered its 2015 forecasts relative to the Oil and Gas Field Services reporting unit. In performing Step I of this interim goodwill impairment test, the estimated fair value of the Oil and Gas Field Services reporting unit was determined using an income approach based upon discounted cash flows and was compared to the reporting unit's carrying value as of June 30, 2015. Based on the results of that valuation, the carrying amount of the reporting unit, including $32.0 million of goodwill, exceeded its estimated fair value and as a result the Company performed Step II of the goodwill impairment test to determine the amount of goodwill impairment charge to be recorded. Step II of the goodwill impairment test required the Company to perform a theoretical purchase price allocation for the reporting unit to determine the implied fair value of goodwill and to compare the implied fair value of goodwill to the recorded amount. The estimates of the fair values of intangible assets identified in performing this theoretical purchase price allocation and resulting implied fair value of goodwill required significant judgment. Based on the results of this goodwill impairment test, the implied value of goodwill was $0 and the Company therefore recognized a goodwill impairment charge equal to the recorded amount of goodwill of $32.0 million as of June 30, 2015. The factors contributing to the $32.0 million goodwill impairment charge principally related to events and changes in circumstances discussed above which had negative impacts on the Company’s prospective financial information utilized in its discounted cash flow model prepared in connection with the interim impairment test. The projected lower levels of activity and pricing in the latter half of the year which became evident during the second quarter decreased the reporting unit’s anticipated future cash flows for 2015 as compared to those estimated previously. These factors also provided evidence of a longer than expected overall recovery from current industry decreased pricing and activity levels which negatively impacted the estimated levels of cash flows in future periods that were assumed in the cash flow models utilized in the interim impairment test. These factors adversely affected the estimated fair value of the reporting unit as of June 30, 2015 and ultimately led to the recognition of the goodwill impairment charge. As of December 31, 2017 and 2016 , the Company's finite-lived and indefinite lived intangible assets consisted of the following (in thousands): December 31, 2017 December 31, 2016 Cost Accumulated Amortization Net Cost Accumulated Amortization Net Permits $ 174,721 $ 74,347 $ 100,374 $ 171,637 $ 67,301 $ 104,336 Customer and supplier relationships 399,224 158,972 240,252 393,426 127,462 265,964 Other intangible assets 36,766 31,592 5,174 34,254 28,456 5,798 Total amortizable permits and other intangible assets 610,711 264,911 345,800 599,317 223,219 376,098 Trademarks and trade names 123,328 — 123,328 122,623 — 122,623 Total permits and other intangible assets $ 734,039 $ 264,911 $ 469,128 $ 721,940 $ 223,219 $ 498,721 The Company continues to monitor those businesses most impacted by the downturn in the oil and energy related markets and also performed an analysis to determine whether the carrying values of the Oil and Gas Field Services and Lodging Services operating segments' finite-lived intangibles and other long lived assets as of December 31, 2017 may not be entirely recoverable. As of December 31, 2017, the Oil and Gas Field Services and Lodging Services operating segments had property, (7) GOODWILL AND OTHER INTANGIBLE ASSETS (Continued) plant and equipment, net of $72.7 million and $95.6 million , respectively, and intangible assets of $2.8 million and $3.9 million , respectively. Based on the analysis performed, sufficient future cash flows are anticipated over those assets' remaining lives to demonstrate recoverability. Thus no impairment charge was recorded related to those other long-lived assets . If expectations of future cash flows were to decrease in the future as a result of worse than expected or prolonged periods of depressed activity, future impairments may become evident. Amortization expense of permits and other intangible assets for the years ended December 31, 2017 , 2016 and 2015 were $37.0 million , $40.0 million and $40.2 million , respectively. The expected amortization of the net carrying amount of finite-lived intangible assets at December 31, 2017 is as follows (in thousands): Years Ending December 31, Expected Amortization 2018 $ 34,631 2019 31,684 2020 29,130 2021 26,888 2022 26,727 Thereafter 196,740 $ 345,800

ACCRUED EXPENSES

ACCRUED EXPENSES	12 Months Ended
	Dec. 31, 2017
Payables and Accruals [Abstract]
ACCRUED EXPENSES	ACCRUED EXPENSES Accrued expenses consisted of the following at December 31 (in thousands): December 31, 2017 December 31, 2016 Insurance $ 57,889 $ 63,061 Interest 12,660 21,536 Accrued compensation and benefits 55,861 34,641 Income, real estate, sales and other taxes 27,330 35,083 Other 34,242 36,400 $ 187,982 $ 190,721 As of December 31, 2017 and 2016 , other accrued expenses included accrued legal matters of $1.4 million and $3.8 million , respectively, and accrued severance charges of $3.5 million and $2.9 million , respectively.

CLOSURE AND POST-CLOSURE LIABIL

CLOSURE AND POST-CLOSURE LIABILITIES	12 Months Ended
	Dec. 31, 2017
Asset Retirement Obligation Disclosure [Abstract]
CLOSURE AND POST-CLOSURE LIABILITIES	CLOSURE AND POST-CLOSURE LIABILITIES The changes to closure and post-closure liabilities (also referred to as "asset retirement obligations") from January 1, 2016 through December 31, 2017 were as follows (in thousands): Landfill Retirement Liability Non-Landfill Retirement Liability Total Balance at January 1, 2016 $ 32,023 $ 24,226 $ 56,249 Liabilities assumed in acquisitions — 2,408 2,408 Measurement period adjustments from prior period acquisitions — 657 657 New asset retirement obligations 1,983 — 1,983 Accretion 2,705 2,398 5,103 Changes in estimates recorded to statement of operations (1,415 ) (1,204 ) (2,619 ) Changes in estimates recorded to balance sheet (3,289 ) — (3,289 ) Expenditures (1,446 ) (802 ) (2,248 ) Currency translation and other 69 18 87 Balance at December 31, 2016 30,630 27,701 58,331 Liabilities assumed in acquisitions — 59 59 Measurement period adjustments from prior period acquisitions — 596 596 New asset retirement obligations 1,881 — 1,881 Adjustment related to disposition of business — (1,170 ) (1,170 ) Accretion 2,243 2,505 4,748 Changes in estimates recorded to statement of operations (131 ) (109 ) (240 ) Changes in estimates recorded to balance sheet 364 (591 ) (227 ) Expenditures (2,777 ) (448 ) (3,225 ) Currency translation and other 172 112 284 Balance at December 31, 2017 $ 32,382 $ 28,655 $ 61,037 All of the landfill facilities included in the above table were active as of December 31, 2017 and 2016 . There were no significant benefits in 2017 and 2016 resulting from changes in estimates for closure and post-closure liabilities. New asset retirement obligations incurred during 2017 and 2016 were discounted at the credit-adjusted risk-free rate of 6.32% and 6.23% , respectively. Anticipated payments (based on current estimated costs and anticipated timing of necessary regulatory approvals to commence work on closure and post-closure activities) for each of the next five years and thereafter are as follows (in thousands): Year ending December 31, 2018 $ 6,313 2019 8,957 2020 12,152 2021 8,652 2022 353 Thereafter 285,404 Undiscounted closure and post-closure liabilities 321,831 Less: Discount at credit-adjusted risk-free rate (161,767 ) Less: Undiscounted estimated closure and post-closure liabilities relating to airspace not yet consumed (99,027 ) Present value of closure and post-closure liabilities $ 61,037

REMEDIAL LIABILITIES

REMEDIAL LIABILITIES	12 Months Ended
	Dec. 31, 2017
Environmental Remediation Obligations [Abstract]
REMEDIAL LIABILITIES	REMEDIAL LIABILITIES The changes to remedial liabilities from January 1, 2016 through December 31, 2017 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, 2016 $ 2,327 $ 63,613 $ 66,052 $ 131,992 Liabilities assumed in acquisitions — — 2,041 2,041 Accretion 110 2,737 2,227 5,074 Changes in estimates recorded to statement of operations (538 ) 1,520 (2,617 ) (1,635 ) Expenditures (122 ) (3,893 ) (5,907 ) (9,922 ) Currency translation and other — 174 283 457 Balance at December 31, 2016 1,777 64,151 62,079 128,007 Measurement period adjustments from prior period acquisitions — — 504 504 Accretion 86 2,648 1,978 4,712 Changes in estimates recorded to statement of operations (21 ) (289 ) 355 45 Expenditures (42 ) (3,906 ) (5,792 ) (9,740 ) Currency translation and other — 2,738 (1,798 ) 940 Balance at December 31, 2017 $ 1,800 $ 65,342 $ 57,326 $ 124,468 There were no significant (benefits) charges in 2017 and 2016 resulting from changes in estimates for remedial liabilities. Anticipated payments at December 31, 2017 (based on current estimated costs and anticipated timing of necessary regulatory approvals to commence work on remedial activities) for each of the next five years and thereafter were as follows (in thousands): Year ending December 31, 2018 $ 14,507 2019 16,934 2020 15,259 2021 10,212 2022 7,566 Thereafter 83,767 Undiscounted remedial liabilities 148,245 Less: Discount (23,777 ) Total remedial liabilities $ 124,468 Based on currently available facts and legal interpretations, existing technology, and presently enacted laws and regulations, the Company estimates that its aggregate liabilities as of December 31, 2017 for future remediation relating to all of its owned or leased facilities and the Superfund sites for which the Company has current or potential future liability is approximately $124.5 million . The Company also estimates that it is reasonably possible that the amount of such total liabilities could be as much as $23.1 million more. Future changes in either available technology or applicable laws or regulations could affect such estimates of remedial liabilities. Since the Company's satisfaction of the liabilities will occur over many years, the Company cannot now reasonably predict the nature or extent of future changes in either available technology or applicable laws or regulations and the impact that those changes, if any, might have on the current estimates of remedial liabilities. The following tables show, respectively, (i) the amounts of such estimated liabilities associated with the types of facilities and sites involved and (ii) the amounts of such estimated liabilities associated with each facility or site which represents at least 5% of the total and with all other facilities and sites as a group and as of December 31, 2017 . (10) REMEDIAL LIABILITIES (Continued) Estimates Based on Type of Facility or Site (in thousands): Type of Facility or Site Remedial Liability % of Total Reasonably Possible Additional Liabilities(1) Facilities now used in active conduct of the Company's business (44 facilities) $ 54,193 43.5 % $ 11,747 Inactive facilities not now used in active conduct of the Company's business but most of which were acquired because the assumption of remedial liabilities for such facilities was part of the purchase price for the CSD assets (38 facilities) 62,706 50.4 10,549 Superfund sites owned by third parties (16 sites) 7,569 6.1 757 Total $ 124,468 100.0 % $ 23,053 ___________________________________ (1) Amounts represent the high end of the range of management's best estimate of the reasonably possible additional liabilities. Estimates Based on Amount of Potential Liability (in thousands): Location Type of Facility or Site Remedial Liability % of Total Reasonably Possible Additional Liabilities(1) Baton Rouge, LA(2) Closed incinerator and landfill $ 23,357 18.8 % $ 3,938 Bridgeport, NJ Closed incinerator 18,394 14.8 2,534 Mercier, Quebec(2) Idled incinerator and legal proceedings 10,414 8.4 1,105 Linden, NJ Operating solvent recycling center 7,678 6.2 825 Various(2) All other incinerators, landfills, wastewater treatment facilities and service centers (78 facilities) 57,056 45.7 13,894 Various(2) Superfund sites (each representing less than 5% of total liabilities) owned by third parties (16 sites) 7,569 6.1 757 Total $ 124,468 100.0 % $ 23,053 _________________________________ (1) Amounts represent the high end of the range of management's best estimate of the reasonably possible additional liabilities. (2) $17.9 million of the $124.5 million remedial liabilities and $1.8 million of the $23.1 million reasonably possible additional liabilities include estimates of remediation liabilities related to the legal and administrative proceedings discussed in Note 17, "Commitments and Contingencies," as well as other such estimated remedial liabilities. Revisions to remediation reserve requirements may result in upward or downward adjustments to income from operations in any given period. The Company believes that its extensive experience in the environmental services business, as well as its involvement with a large number of sites, provides a reasonable basis for estimating its aggregate liability. It is possible, however, that technological, regulatory or enforcement developments, the results of environmental studies, or other factors could necessitate the recording of additional liabilities or the revision of currently recorded liabilities that could be material. The impact of such future events cannot be estimated at the current time.

FINANCING ARRANGEMENTS

FINANCING ARRANGEMENTS	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
FINANCING ARRANGEMENTS	FINANCING ARRANGEMENTS The following table is a summary of the Company's financing arrangements (in thousands): December 31, 2017 December 31, 2016 Senior secured Term Loan Agreement ("Term Loan Agreement") $ 4,000 $ — Current portion of long-term obligations, at carrying value $ 4,000 $ — Senior secured Term Loan Agreement due June 30, 2024 $ 394,000 $ — Senior unsecured notes, at 5.25%, due August 1, 2020 ("2020 Notes") 400,000 800,000 Senior unsecured notes, at 5.125%, due June 1, 2021 ("2021 Notes") 845,000 845,000 Long-term obligations, at par $ 1,639,000 $ 1,645,000 Unamortized debt issuance costs and premium, net $ (13,463 ) $ (11,728 ) Long-term obligations, at carrying value $ 1,625,537 $ 1,633,272 Senior Secured Term Loan. On June 30, 2017, the Company, and substantially all of the Company’s domestic subsidiaries as guarantors, entered into a $400.0 million senior secured term loan agreement (the "Term Loan Agreement"). Loans under the Term Loan Agreement will mature on June 30, 2024 and may be prepaid at any time without premium or penalty other than customary breakage costs with respect to Eurodollar based loans. The Company’s obligations under the Term Loan Agreement are guaranteed by all of the Company’s domestic restricted subsidiaries and secured by liens on substantially all of the assets of the Company and the guarantors. Borrowings under the Term Loan Agreement bear interest, at the Company’s election, at either of the following rates: (a) the sum of the Eurodollar Rate (as defined in the Term Loan Agreement) plus 2.00% , or (b) the sum of the Base Rate (as defined in the Term Loan Agreement) plus 1.00% , with the Eurodollar Rate being subject to a floor of 0.00% . The effective interest rate of the Term Loan on December 31, 2017 was 3.57% . The Term Loan Agreement contains representations and warranties, affirmative and negative covenants, and events of default, which the Company believes are usual and customary for an agreement of this type. Such covenants restrict the Company’s ability, among other matters, to incur debt, create liens on the Company’s assets, make restricted payments or investments or enter into transactions with affiliates. In accordance with the Term Loan Agreement required payments equal to .25% of the initial $400.0 million are due upon the last day of each calendar quarter. Upon entering into the Term Loan Agreement on June 30, 2017, the Company used approximately $312.6 million of the proceeds to purchase approximately $296.2 million aggregate principal amount (the “Repurchased Notes”) of the Company’s previously outstanding 2020 Notes and pay accrued interest of approximately $6.4 million on the Repurchased Notes. On June 30, 2017, the Company also delivered a partial notice of redemption to the holders of the approximately $503.8 million aggregate principal amount of 2020 Notes which remained outstanding after the purchase of the Repurchased Notes. Pursuant to that notice, the Company redeemed on August 1, 2017 $103.8 million aggregate principal amount of 2020 Notes at a redemption price of 101.313% plus accrued but unpaid interest. The Company financed the redemption through the remaining net proceeds of the Term Loan Agreement financing described above, plus available cash. In conjunction with such redemption, the Company paid premiums to repay the debt early of $6.0 million and incurred expenses of approximately $6.5 million . At December 31, 2017 , the fair value of the Term Loan Agreement debt was $400.5 million based on quoted market prices or other available market data. The fair value of the Term Loan Agreement debt is considered a Level 2 measure according to the fair value hierarchy. Senior Unsecured Notes. On July 30, 2012, the Company issued $800.0 million aggregate principal amount of 5.25% senior unsecured notes due August 1, 2020 (the "2020 Notes") with semi-annual fixed interest payments on February 1 and August 1 of each year. As described above, the Company repurchased or redeemed $400.0 million principal amount of the 2020 Notes during 2017. At December 31, 2017 and December 31, 2016 , the fair value of the 2020 Notes was $404.6 million and $820.0 million , respectively, based on quoted market prices for the instrument. The fair value of the 2020 Notes is considered a Level 2 measure according to the fair value hierarchy. The Company may redeem some or all of the 2020 Notes which remain outstanding at any time upon proper notice, at the following redemption prices plus unpaid interest: Year Percentage Prior to August 1, 2018 101.313 % On or after August 1, 2018 100.000 % (11) FINANCING ARRANGEMENTS (Continued) On December 7, 2012, the Company issued $600.0 million aggregate principal amount of 5.125% senior unsecured notes due 2021 (the "2021 Notes") with semi-annual fixed interest payments on June 1 and December 1 of each year. The Company used the net proceeds from such issuance to fund a portion of the purchase price to acquire Safety-Kleen. The Company repurchased $5.0 million principal amount of 2021 Notes during 2014. On March 14, 2016, the Company issued an additional $ 250.0 million aggregate principal amount of 2021 Notes as additional notes under the indenture. At December 31, 2017 and 2016 , the fair value of the Company's 2021 Notes was $855.7 million and $861.9 million , respectively, based on quoted market prices or other available market data. The fair value of the 2021 Notes is considered a Level 2 measure according to the fair value hierarchy. The Company may redeem some or all of the 2021 Notes at any time upon proper notice, at the following redemption prices plus unpaid interest: Year Percentage Prior to December 1, 2018 101.281 % On or after December 1, 2018 100.000 % The 2020 Notes and 2021 Notes (collectively, the "Senior Unsecured Notes") and the related indentures contain various customary non-financial covenants and are guaranteed by substantially all of the Company's current and future domestic restricted subsidiaries. The Senior Unsecured Notes are the Company's and the guarantors' senior unsecured obligations ranking equally with the Company's and the guarantors' existing and future senior unsecured obligations and senior to any future indebtedness that is expressly subordinated to the Notes and the guarantees. The Senior Unsecured Notes are effectively subordinated to all of the Company's and the Company subsidiaries' secured indebtedness under the Company's Term Loan Agreement, revolving credit facility and capital lease obligations to the extent of the value of the assets securing such secured indebtedness. The Senior Unsecured Notes are not guaranteed by the Company's existing and future Canadian or other foreign subsidiaries, and are structurally subordinated to all indebtedness and other liabilities, including trade payables, of the Company's subsidiaries that are not guarantors of the Senior Unsecured Notes. Revolving Credit Facility. On November 1, 2016, the Company and one of the Company's subsidiaries (the "Canadian Borrower") entered into an amended and restated credit agreement for the Company's revolving credit facility with Bank of America, N.A. (“BofA”), as agent for the lenders under the facility (the "Agent"). Under the amended and restated facility, the Company has the right to obtain revolving loans and letters of credit for a combined maximum of up to $300.0 million (with a sub-limit of $250.0 million for letters of credit) and the Canadian Borrower has the right to obtain revolving loans and letters of credit for a combined maximum of up to $100.0 million (with a $75.0 million sub-limit for letters of credit). Availability under the U.S. line is subject to a borrowing base basically comprised of 85% of the eligible accounts receivable of the Company and its U.S. subsidiaries plus 100% of cash deposited in a controlled account with the Agent, and availability under the Canadian line is subject to a borrowing base basically comprised of 85% of the eligible accounts receivable of the Company’s Canadian subsidiaries plus 100% of cash deposited in a controlled account with the Agent’s Canadian affiliate. Subject to certain conditions, the facility will expire on November 1, 2021. Borrowings under the revolving credit facility bear interest at a rate of, at the Company’s option, either (i) LIBOR plus an applicable margin ranging from 1.25% to 1.50% per annum based primarily on the level of the Company’s average liquidity for the most recent 30 day period or (ii) BofA’s base rate plus an applicable margin ranging from 0.25% to 0.50% per annum based primarily on such average liquidity. There is also an unused line fee, calculated on the then unused portion of the lenders’ $400.0 million maximum commitments, ranging from 0.25% to 0.30% per annum of the unused commitment. For outstanding letters of credit, the Company will pay to the lenders a fee equal to the then applicable LIBOR margin described above, and to the issuing banks a standard fronting fee and customary fees and charges in connection with all amendments, extensions, draws and other actions with respect to letters of credit. The Company’s obligations under the revolving credit facility (including revolving loans and reimbursement obligations for outstanding letters of credit) are guaranteed by substantially all of the Company’s U.S. subsidiaries and secured by a first lien on the Company’s and its U.S. subsidiaries’ accounts receivable. The Canadian Borrower’s obligations under the facility are guaranteed by substantially all of the Company’s Canadian subsidiaries and secured by a first lien on the accounts receivable of the Canadian subsidiaries. The Company and its U.S. subsidiaries guarantee the obligations of the Canadian subsidiaries under the facility, but the Canadian subsidiaries do not guarantee and are not otherwise responsible for the obligations of the Company and its U.S. subsidiaries. (11) FINANCING ARRANGEMENTS (Continued) The Company utilizes letters of credit primarily as security for financial assurance which it has been required to provide to regulatory bodies for its hazardous waste facilities and which would be called only in the event that the Company fails to satisfy closure, post-closure and other obligations under the permits issued by those regulatory bodies for such licensed facilities. At December 31, 2017 and 2016 , the revolving credit facility had no outstanding loan balances, availability of $217.8 million and $195.2 million , respectively, and outstanding letters of credit of $134.1 million and $132.6 million , respectively.

INCOME TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES The domestic and foreign components of income before (benefit) provision for income taxes were as follows (in thousands): For the Year Ended December 31, 2017 2016 2015 Domestic $ 101,714 $ 87,328 $ 164,105 Foreign (43,025 ) (78,612 ) (54,459 ) Total $ 58,689 $ 8,716 $ 109,646 The (benefit) provision for income taxes consisted of the following (in thousands): For the Year Ended December 31, 2017 2016 2015 Current: Federal $ 25,613 $ 14,798 $ 46,775 State 11,083 8,763 11,120 Foreign 4,589 9,844 5,719 41,285 33,405 63,614 Deferred Federal (85,488 ) 21,814 12,254 State 1,085 1,644 2,766 Foreign 1,068 (8,274 ) (13,090 ) (83,335 ) 15,184 1,930 (Benefit) provision for income taxes $ (42,050 ) $ 48,589 $ 65,544 The Company's effective tax rate for fiscal years 2017 , 2016 and 2015 was (71.6)% , 557.5% and 59.8% , respectively. The effective income tax rate varied from the amount computed using the statutory federal income tax rate as follows (in thousands): For the Year Ended December 31, 2017 2016 2015 Tax expense at US statutory rate $ 20,541 $ 3,051 $ 38,376 State income taxes, net of federal benefit 4,547 6,010 8,449 Foreign rate differential 3,733 3,646 3,951 Valuation allowance 16,552 22,564 1,824 Uncertain tax position interest and penalties 3,730 107 32 Goodwill impairment — 11,905 10,974 Other 1,856 1,306 1,938 Adjustment for Tax Cuts and Jobs Act (93,009 ) — — (Benefit) provision for income taxes $ (42,050 ) $ 48,589 $ 65,544 (12) INCOME TAXES (Continued) Effects of the Tax Cuts and Jobs Act On December 22, 2017, the “Tax Cuts and Jobs Act” (the “Tax Act”) was signed into law, making significant changes to the federal tax law. Changes include, but are not limited to, a corporate tax rate decrease from 35% to 21% effective for tax years beginning after December 31, 2017, the transition of U.S. international taxation from a worldwide tax system to a territorial tax system, and a one-time transition tax on the mandatory deemed repatriation of cumulative foreign earnings as of December 31, 2017. The Company has calculated its best estimate of the impact of the Tax Act in its year end income tax provision in accordance with its understanding of the Tax Act and guidance available as of the date of this filing and as a result has recorded a net benefit of $93.0 million as a component of income tax expense in the fourth quarter of 2017, the period in which the legislation was enacted. This provisional net income tax benefit is comprised of a $100.5 million tax benefit for the remeasurement of deferred tax assets and liabilities to the 21% rate at which they are expected to reverse, offset by a one-time tax expense on deemed repatriation of $7.5 million . This one-time charge is after the utilization of $7.5 million of foreign tax credits which had full valuation allowances applied to them previously. This one-time tax expense is expected to be paid over a period of eight years. Due to the timing of the Tax Act and potential uncertainty or diversity of views in accounting for the impact of the Tax Act, the SEC provided guidance in SAB 118 on accounting for the tax effects of the Tax Act (See Note 2, “Significant Accounting Policies”). In accordance with that guidance, the Company has determined that the components of the net benefit of $93.0 million recorded in the fourth quarter of 2017 were provisional amounts and reasonable estimates at December 31, 2017. Additional work is necessary to do a more detailed analysis of all provisional amounts associated with the Tax Act referenced above as a result of pending issuance of Notices and Regulations related to the Tax Act and finalization of foreign earnings and profits for 2017. The Company will continue 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. During the year ended December 31, 2016, the Company allocated $16.8 million of tax benefits related to tax deductible foreign currency losses to accumulated other comprehensive loss and as such these benefits are not included within the (benefit) provision for income taxes. (12) INCOME TAXES (Continued) The components of the total net deferred tax assets and liabilities at December 31, 2017 and 2016 were as follows (in thousands): 2017 2016 Deferred tax assets: Provision for doubtful accounts 7,417 11,189 Closure, post-closure and remedial liabilities 28,189 40,829 Accrued expenses 15,382 19,826 Accrued compensation 1,903 2,747 Net operating loss carryforwards(1) 46,650 46,752 Tax credit carryforwards(2) 17,504 25,348 Uncertain tax positions accrued interest and federal benefit 921 1,241 Stock-based compensation 2,268 1,993 Other 3,258 555 Total deferred tax assets 123,492 150,480 Deferred tax liabilities: Property, plant and equipment (144,325 ) (207,799 ) Permits and other intangible assets (107,407 ) (161,295 ) Prepaids (8,080 ) (11,030 ) Total deferred tax liabilities (259,812 ) (380,124 ) Total net deferred tax liability before valuation allowance (136,320 ) (229,644 ) Less valuation allowance (68,355 ) (55,189 ) Net deferred tax liabilities $ (204,675 ) $ (284,833 ) ___________________________________ (1) As of December 31, 2017 , the net operating loss carryforwards included (i) state net operating loss carryovers of $186.7 million which will begin to expire in 2018, (ii) federal net operating loss carryforwards of $48.0 million which will begin to expire in 2025, and (iii) foreign net operating loss carryforwards of $116.1 million which will begin to expire in 2018. (2) As of December 31, 2017 , the foreign tax credit carryforwards of $17.5 million will expire between 2020 and 2024. The Company has not accrued for any remaining undistributed foreign earnings not subject to the one-time transition tax on mandatory deemed repatriation of cumulative foreign earnings. These amounts continue to be indefinitely reinvested in foreign operations. A valuation allowance is required to be established when, based on an evaluation of available evidence, it is more likely than not that some portion or all of the deferred tax assets will not be realized. Accordingly, as of December 31, 2017 and 2016 , the Company had a valuation allowance of $68.4 million and $55.2 million , respectively. The total allowance as of December 31, 2017 consisted of $17.5 million of foreign tax credits, $3.9 million of acquired federal net operating losses, $11.9 million of state net operating loss carryforwards, $22.6 million of foreign net operating loss carryforwards, and $12.5 million of deferred tax assets of a Canadian subsidiary. The allowance as of December 31, 2016 consisted of $25.0 million of foreign tax credits, $1.5 million of acquired federal net operating losses, $5.0 million of state net operating loss carryforwards and $18.0 million of foreign net operating loss carryforwards and $5.7 million of deferred tax assets of a Canadian subsidiary. The change in valuation allowance in 2017 was impacted by incremental allowance recorded on net operating losses generated by certain Canadian subsidiaries in 2017 for which the Company is currently recording a full valuation allowance against. This increase was offset by a $7.5 million decrease due to the reversal of allowances resulting from impacts of the enactment of the Tax Act and specifically the utilization of foreign tax credits in connection with the one-time transition tax on the mandatory deemed repatriation of cumulative foreign earnings. The foreign tax credits utilized had previously had full valuation allowances recorded against them. The valuation allowances attributable to foreign tax assets are due to the significant downturn in the operations of certain of the Company’s Canadian businesses in current and recent years and uncertainty as to whether these (12) INCOME TAXES (Continued) Canadian businesses will generate sufficient future taxable income to utilize these deferred tax assets. The Company therefore concluded that the recording of valuation allowances were required as of December 31, 2017. The changes to unrecognized tax benefits (excluding related penalties and interest) from January 1, 2015 through December 31, 2017 , were as follows (in thousands): 2017 2016 2015 Unrecognized tax benefits as of January 1 $ 1,738 $ 2,064 $ 2,537 Additions to current year tax positions 1,457 — — Additions to prior year tax positions 2,031 — — Settlements (231 ) (533 ) (217 ) Foreign currency translation 126 207 (256 ) Unrecognized tax benefits as of December 31 $ 5,121 $ 1,738 $ 2,064 At December 31, 2017 , 2016 and 2015 , the Company had recorded $5.1 million , $1.7 million and $2.1 million , respectively, of unrecognized tax benefits that if recognized would affect the annual effective tax rate. The Company's policy is to recognize interest and penalties related to income tax matters as a component of income tax expense. The liability for unrecognized tax benefits at December 31, 2017 included accrued interest of $0.9 million , $0.3 million and $0.4 million for the payment of interest accrued at December 31, 2017 , 2016 and 2015 , respectively. Interest expense that is recorded as a tax expense against the liability for unrecognized tax benefits for the years ended December 31, 2017 , 2016 and 2015 included interest and penalties of $0.5 million , $0.1 million and $0.1 million , respectively. The Company files U.S. federal income tax returns as well as income tax returns in various states and foreign jurisdictions. The Company may be subject to examination by the Internal Revenue Service (the "IRS") for calendar years 2014 through 2016. Additionally, any net operating losses that were generated in prior years and utilized in these years may also be subject to examination by the IRS. The Company may also be subject to examinations by state and local revenue authorities for calendar years 2013 through 2016. The Company is currently not under examination by the IRS. The Company has ongoing U.S. state and local jurisdictional audits, as well as Canadian federal and provincial audits, all of which the Company believes will not result in material liabilities. Due to expiring statute of limitation periods and the resolution of tax audits, the Company believes that total unrecognized tax benefits will decrease by approximately $1.4 million within the next 12 months.

EARNINGS (LOSS) PER SHARE

EARNINGS (LOSS) PER SHARE	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
(LOSS) EARNINGS PER SHARE	EARNINGS (LOSS) PER SHARE The following are computations of basic and diluted earnings (loss) per share (in thousands except for per share amounts): Years Ended December 31, 2017 2016 2015 Numerator for basic and diluted earnings (loss) per share: Net income (loss) $ 100,739 $ (39,873 ) $ 44,102 Denominator: Weighted basic shares outstanding 57,072 57,532 58,324 Dilutive effect of equity-based compensation awards 128 — 110 Weighted dilutive shares outstanding 57,200 57,532 58,434 Basic earnings (loss) per share $ 1.77 $ (0.69 ) $ 0.76 Diluted earnings (loss) per share $ 1.76 $ (0.69 ) $ 0.76 For the year ended December 31, 2017 , all then outstanding restricted stock awards and performance awards were included in the calculation of diluted earnings per share except for 152,831 of outstanding performance stock awards for which the performance criteria were not attained at the time and 49,373 restricted stock awards which were excluded as their inclusion (13) EARNINGS (LOSS) PER SHARE (Continued) would have an antidilutive effect. As a result of the net loss reported for the year ended December 31, 2016 , all outstanding stock options, restricted stock awards and performance awards, totaling 730,929 potentially dilutive shares, were excluded from the calculation of diluted loss per share as their inclusion would have an antidilutive effect. For the year ended December 31, 2015 , all then outstanding stock options, restricted stock awards and performance awards were included in the calculation of diluted earnings per share except for 154,577 of outstanding performance stock awards for which the performance criteria were not attained at the time and 31,656 restricted stock awards which were excluded as their inclusion would have an antidilutive effect.

STOCKHOLDERS' EQUITY

STOCKHOLDERS' EQUITY	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
STOCKHOLDERS' EQUITY	STOCKHOLDERS' EQUITY 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 . The Company has funded and intends to continue to fund the repurchases through available cash resources. The repurchase program authorizes the Company to purchase the Company's common stock on the open market or in privately negotiated transactions periodically in a manner that complies with applicable U.S. securities laws. The number of shares purchased and the timing of the purchases has depended and will depend on a number of factors including share price, cash required for future business plans, trading volume and other conditions. The Company has no obligation to repurchase stock under this program and may suspend or terminate the repurchase program at any time. During the years ended December 31, 2017 , 2016 and 2015 , the Company repurchased and retired a total of approximately 0.9 million , 0.5 million and 1.4 million shares, respectively, of the Company's common stock for total costs of approximately $49.0 million , $22.2 million and $73.3 million , respectively. Through December 31, 2017 , the Company has repurchased and retired a total of approximately 4.8 million shares of its common stock for approximately $248.8 million under this program. As of December 31, 2017 , an additional $351.2 million remained available for repurchase of shares under this program.

ACCUMULATED OTHER COMPREHENSIVE

ACCUMULATED OTHER COMPREHENSIVE LOSS	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
ACCUMULATED OTHER COMPREHENSIVE LOSS	ACCUMULATED OTHER COMPREHENSIVE LOSS The changes in accumulated other comprehensive loss by component and related tax effects for the years ended December 31, 2017 , 2016 and 2015 were as follows (in thousands): Foreign Currency Translation Adjustments Unrealized (Losses) Gains on Available-for-Sale Securities Unfunded Pension Liability Total Balance at January 1, 2015 $ (108,889 ) $ — $ (1,953 ) $ (110,842 ) Other comprehensive loss before reclassifications (144,050 ) — (7 ) (144,057 ) Amounts reclassified out of accumulated other comprehensive loss — — — — Tax effects — — 7 7 Other comprehensive loss (144,050 ) — — (144,050 ) Balance at December 31, 2015 $ (252,939 ) $ — $ (1,953 ) $ (254,892 ) Other comprehensive income (loss) before reclassifications 23,967 (535 ) 216 23,648 Amounts reclassified out of accumulated other comprehensive loss — — — — Tax effects 16,761 214 (57 ) 16,918 Other comprehensive income (loss) 40,728 (321 ) 159 40,566 Balance at December 31, 2016 $ (212,211 ) $ (321 ) $ (1,794 ) $ (214,326 ) Other comprehensive income before reclassifications 41,636 184 146 41,966 Amounts reclassified out of accumulated other comprehensive loss — 222 — 222 Tax effects — (231 ) (38 ) (269 ) Other comprehensive income 41,636 175 108 41,919 Balance at December 31, 2017 $ (170,575 ) $ (146 ) $ (1,686 ) $ (172,407 ) During the year ended December 31, 2016, the Company converted an intercompany loan with a foreign subsidiary to equity, which resulted in a loss for tax purposes. The loan had been historically treated as a component of the Company’s investment in that subsidiary, and as a result, foreign currency gains and losses on the loan had been accumulated as a component of other comprehensive income. The subsidiary continues to operate as part of the Company. The tax benefit of $16.8 million , which was triggered by the conversion, was therefore allocated to other comprehensive income (loss) rather than net (loss) income. (15) ACCUMULATED OTHER COMPREHENSIVE LOSS (Continued) The amounts reclassified out of accumulated other comprehensive loss into the consolidated statement of operations, with presentation location, during the year ended December 31, 2017 were as follows (in thousands): Other Comprehensive Income Components December 31, 2017 Location Unrealized (losses) gains on available-for-sale securities $ (222 ) Other (expense) income, net There were no reclassifications out of accumulated other comprehensive loss during the years ended December 31, 2016 and 2015 .

STOCK-BASED COMPENSATION AND EM

STOCK-BASED COMPENSATION AND EMPLOYEE BENEFIT PLANS	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
STOCK-BASED COMPENSATION AND EMPLOYEE BENEFIT PLANS	STOCK-BASED COMPENSATION AND EMPLOYEE BENEFIT PLANS Stock-Based Compensation In 2000, the Company adopted a stock incentive plan (the "2000 Plan"), which provided for awards in the form of incentive stock options, non-qualified stock options, restricted stock awards, performance stock awards and common stock awards. The 2000 Plan expired on April 15, 2010 and as of December 31, 2017 , no options remained outstanding under that plan. In 2010, the Company adopted an equity incentive plan (the "2010 Plan"), which provides for awards of up to 6,000,000 shares of common stock (subject to certain anti-dilution adjustments) in the form of (i) stock options, (ii) stock appreciation rights, (iii) restricted stock, (iv) restricted stock units, and (v) certain other stock-based awards. The Company ceased issuing stock options in 2008, and all awards issued to date under the 2010 Plan have been in the form of restricted stock awards and performance stock awards as described below. As of December 31, 2017 and 2016 , the Company had the following types of stock-based compensation awards outstanding under the 2000 Plan and the 2010 Plan (collectively, the "Plans"): stock options, restricted stock awards and performance stock awards. The restricted stock awards generally vest over three to five years subject to continued employment. The performance stock awards vest depending on the satisfaction of certain performance criteria and continued service conditions as described below. Total stock-based compensation cost charged to selling, general and administrative expenses for the years ended December 31, 2017 , 2016 and 2015 was $13.1 million , $10.5 million and $8.6 million , respectively. The total income tax benefit recognized in the consolidated statements of operations from stock-based compensation was $3.7 million , inclusive of $0.4 million from excess tax benefits on vested awards, $2.8 million and $2.3 million for the years ended December 31, 2017 , 2016 and 2015 , respectively. Restricted Stock Awards The following information relates to restricted stock awards that have been granted to employees and directors under the Company's 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 year ended December 31, 2017 : Restricted Stock Number of Shares Weighted Average Grant-Date Fair Value Unvested at January 1, 2017 510,041 $ 52.65 Granted 307,455 55.93 Vested (136,787 ) 53.16 Forfeited (75,776 ) 52.46 Unvested at December 31, 2017 604,933 $ 54.23 As of December 31, 2017 , there was $24.1 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 2.8 years. The (16) STOCK-BASED COMPENSATION AND EMPLOYEE BENEFIT PLANS (Continued) total fair value of restricted stock vested during 2017 , 2016 and 2015 was $7.3 million , $8.3 million and $6.9 million , respectively. Performance Stock Awards The following information relates to performance stock awards that have been granted to employees under the Company's Plans. The compensation committee of the Company's board of directors established two -year performance targets which could potentially be achieved in the year granted or one year thereafter. Performance stock awards are subject to performance criteria established by the compensation committee of the Company's board of directors 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, 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 then considered probable. The following table summarizes information about performance stock awards for the year ended December 31, 2017 : Performance Stock Number of Shares Weighted Average Grant-Date Fair Value Unvested at January 1, 2017 220,882 $ 54.69 Granted 170,897 55.87 Vested (53,096 ) 55.60 Forfeited (148,554 ) 57.14 Unvested at December 31, 2017 190,129 $ 55.63 As of December 31, 2017 , there was $2.5 million of total unrecognized compensation cost arising from non-vested compensation related to performance stock awards then deemed probable of vesting under the Company's Plans. The total fair value of performance awards vested during 2017 , 2016 and 2015 was $3.0 million , $1.0 million and $0.6 million , respectively. Employee Benefit Plans As of December 31, 2017 , the Company has responsibility for a defined benefit plan that covered 12 active non-supervisory Canadian employees. For the years ended December 31, 2017 and 2016, net periodic pension costs were $0.4 million . For the year ended December 31, 2015 , net periodic pension cost was $0.3 million . At December 31, 2017 , the fair value of the Company's plan assets was $9.3 million . The fair value of $3.9 million of these plan assets was considered a Level 1 measure and the fair value of $5.4 million of these plan assets was considered a Level 2 measure, according to the fair value hierarchy . At December 31, 2016 , the fair value of the Company's plan assets was $8.4 million . The fair value of $3.5 million of these plan assets was considered a Level 1 measure and the fair value of $4.9 million of these plan assets was considered a Level 2 measure, according to the fair value hierarchy . As of December 31, 2017 and 2016 , the projected benefit obligation was $10.9 million and $9.9 million , respectively.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	12 Months Ended
	Dec. 31, 2017
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 December 31, 2017 and December 31, 2016 , the Company had recorded reserves of $19.3 million and $22.0 million , respectively, in the Company's financial statements for actual or probable liabilities related to the legal and administrative proceedings in which the Company was then involved, the principal of which are described below. At December 31, 2017 and December 31, 2016 , the Company also believed that it was reasonably possible that the amount of these potential liabilities could be as much as $1.8 million and $1.9 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 December 31, 2017 and December 31, 2016 , the $19.3 million and $22.0 million , respectively, of reserves consisted of (i) $17.9 million and $18.2 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) $1.4 million and $3.8 million , respectively, primarily related to federal, state and provincial enforcement actions, which were included in accrued expenses on the consolidated balance sheets. As of December 31, 2017 , the principal legal and administrative proceedings in which the Company was involved, or which had been terminated during 2017 , 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 December 31, 2017 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 52 proceedings (excluding cases which have been settled but not formally dismissed) as of December 31, 2017 , wherein persons claim personal injury resulting from the use of Safety-Kleen's parts cleaning equipment or cleaning products. These proceedings typically involve allegations that the solvent used in Safety-Kleen's parts cleaning equipment contains contaminants and/or that Safety-Kleen's recycling process does not effectively remove the contaminants that become entrained in the solvent during their use. In addition, certain claimants assert that Safety-Kleen failed to warn adequately the product user of potential risks, including a historic failure to warn that solvent contains trace amounts of toxic or hazardous substances such as benzene. Safety-Kleen maintains insurance that it believes will provide coverage for these product liability claims (over amounts accrued for self-insured retentions and deductibles in certain limited cases), except for punitive damages to the extent not insurable under state law or excluded from insurance coverage. Safety-Kleen also believes that these claims lack merit and has historically vigorously defended, and intends to continue to vigorously defend, itself and the safety of its products against all of these claims. Such matters are subject to many uncertainties and outcomes are not predictable with assurance. Consequently, Safety-Kleen is unable to ascertain the ultimate aggregate amount of monetary liability or financial impact with respect to these matters as of December 31, 2017 . From January 1, 2017 to December 31, 2017 , 33 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 (17) COMMITMENTS AND CONTINGENCIES (Continued) 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 129 sites which are subject to or are proposed to become subject to proceedings under federal or state Superfund laws. Of the 129 sites, three (including the BR Facility described below) involve facilities that are now owned or leased by the Company and 126 involve third-party sites to which either the Company or the prior owners of certain of the Company’s facilities shipped wastes. Of the 126 third-party sites, 33 are now settled, 16 are currently requiring expenditures on remediation and 77 are not currently requiring expenditures on remediation. In connection with each site, the Company has estimated the extent, if any, to which it may be subject, either directly or as a result of any indemnification obligations, for cleanup and remediation costs, related legal and consulting costs associated with PRP investigations, settlements, and related legal and administrative proceedings. The amount of such actual and potential liability is inherently difficult to estimate because of, among other relevant factors, uncertainties as to the legal liability (if any) of the Company or the prior owners of certain of the Company's facilities to contribute a portion of the cleanup costs, the assumptions that must be made in calculating the estimated cost and timing of remediation, the identification of other PRPs and their respective capability and obligation to contribute to remediation efforts, and the existence and legal standing of indemnification agreements (if any) with prior owners, which may either benefit the Company or subject the Company to potential indemnification obligations. The Company believes its potential liability could exceed $100,000 at 11 of the 126 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 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 126 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 126 third-party sites discussed above. Federal, State and Provincial Enforcement Actions From time to time, the Company pays fines or penalties in regulatory proceedings relating primarily to waste treatment, storage or disposal facilities. As of December 31, 2017 and 2016 , 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. (17) COMMITMENTS AND CONTINGENCIES (Continued) Leases The Company leases facilities, service centers and personal property under certain operating leases. Some of these lease agreements contain an escalation clause for increased taxes and operating expenses and are renewable at the option of the Company. Lease terms range from 1 to 24 years. The following is a summary of future minimum payments under operating leases that have initial or remaining non-cancelable lease terms in excess of one year at December 31, 2017 (in thousands): Year Total Operating Leases 2018 $ 44,476 2019 37,161 2020 30,233 2021 22,173 2022 17,432 Thereafter 45,370 Total minimum lease payments $ 196,845 During the years ended December 31, 2017 , 2016 and 2015 , rent expense including short-term rentals was approximately $125.4 million , $121.9 million , and $135.5 million , respectively. Other Contingencies Under the Company's insurance programs, coverage is obtained for catastrophic exposures, as well as those risks required to be insured by law or contract. The Company's policy is to retain a significant portion of certain expected losses related to workers' compensation, health insurance, comprehensive general liability and vehicle liability. A portion of these self-insured liabilities are managed through its wholly-owned captive insurance subsidiary. Provisions for losses expected under these programs are recorded based upon the Company's estimates of the aggregate liability for claims. The deductible per participant per year for the health insurance policy is $0.7 million . The deductible per occurrence for workers' compensation is $1.0 million , general liability is $2.0 million and vehicle liability is $2.0 million . The retention per claim for the environmental impairment policy is $1.0 million . At December 31, 2017 and 2016 , the Company had accrued $47.9 million and $46.5 million , respectively, for its self-insurance liabilities (exclusive of health insurance) using a risk-free discount rate of 1.87% and 1.16% , respectively. Actual expenditures in future periods can differ materially from accruals based on estimates. Anticipated payments for contingencies related to workers' compensation, comprehensive general liability and vehicle liability related claims at December 31, 2017 for each of the next five years and thereafter were as follows (in thousands): Years ending December 31, 2018 $ 16,525 2019 11,259 2020 7,848 2021 4,393 2022 3,688 Thereafter 5,769 Undiscounted self-insurance liabilities 49,482 Less: Discount 1,568 Total self-insurance liabilities (included in accrued expenses) $ 47,914

SEGMENT REPORTING

SEGMENT REPORTING	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
SEGMENT REPORTING	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 its business, makes operating decisions and assesses performance. The Company's operations are managed in six operating segments: Technical Services, Industrial Services, Field Services, Safety-Kleen, Oil and Gas Field Services and Lodging Services. For purposes of segment disclosure the Industrial Services and Field Services operating segments have been aggregated into a single reportable segment based upon their similar (18) SEGMENT REPORTING (Continued) economic and other characteristics, and the Oil and Gas Field Services and Lodging Services operating segments have been combined as they do not meet the quantitative thresholds for separate presentation. 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 years ended December 31, 2017 , 2016 and 2015 (in thousands): For the Year Ended December 31, 2017 Technical Services Industrial and Field Services Safety-Kleen Oil, Gas and Lodging Services Corporate Items Totals Third-party revenues $ 980,232 $ 631,216 $ 1,213,703 $ 117,252 $ 2,575 $ 2,944,978 Intersegment revenues, net 161,533 (37,694 ) (125,822 ) 1,983 — — Corporate Items, net 2,384 200 5 368 (2,957 ) — Direct revenues $ 1,144,149 $ 593,722 $ 1,087,886 $ 119,603 $ (382 ) $ 2,944,978 For the Year Ended December 31, 2016 Technical Services Industrial and Field Services Safety-Kleen Oil, Gas and Lodging Services Corporate Items Totals Third-party revenues $ 906,495 $ 618,245 $ 1,110,727 $ 116,692 $ 3,067 $ 2,755,226 Intersegment revenues, net 147,866 (35,724 ) (115,013 ) 2,871 — — Corporate Items, net 2,374 (306 ) 369 320 (2,757 ) — Direct revenues $ 1,056,735 $ 582,215 $ 996,083 $ 119,883 $ 310 $ 2,755,226 For the Year Ended December 31, 2015 Technical Services Industrial and Field Services Safety-Kleen Oil, Gas and Lodging Services Corporate Items Totals Third-party revenues $ 991,410 $ 1,023,638 $ 1,060,926 $ 198,705 $ 458 $ 3,275,137 Intersegment revenues, net 144,084 (32,903 ) (119,232 ) 8,051 — — Corporate Items, net 3,586 (782 ) (5 ) 383 (3,182 ) — Direct revenues $ 1,139,080 $ 989,953 $ 941,689 $ 207,139 $ (2,724 ) $ 3,275,137 The primary financial measure by which the Company evaluates the performance of its segments is Adjusted EBITDA which consists of net income (loss) plus accretion of environmental liabilities, depreciation and amortization, net interest expense, loss on early extinguishment of debt, (benefit) provision for income taxes, other gains or non-cash charges (including gain on sale of businesses and goodwill impairment charges) not deemed representative of fundamental segment results and excludes other expense (income), net. Transactions between the segments are accounted for at the Company’s best estimate based on similar transactions with outside customers. (18) SEGMENT REPORTING (Continued) The following table presents Adjusted EBITDA information used by management by reported segment (in thousands): For the Year Ended December 31, 2017 2016 2015 Adjusted EBITDA: Technical Services $ 276,592 $ 271,176 $ 291,737 Industrial and Field Services 43,010 51,191 161,447 Safety-Kleen 249,811 219,546 172,262 Oil, Gas and Lodging Services 1,708 (3,292 ) 11,704 Corporate Items (145,464 ) (138,267 ) (132,983 ) Total 425,657 400,354 504,167 Reconciliation to Consolidated Statements of Operations: Accretion of environmental liabilities 9,460 10,177 10,402 Depreciation and amortization 288,422 287,002 274,194 Goodwill impairment charges — 34,013 31,992 Income from operations 127,775 69,162 187,579 Other expense (income), net 6,119 (6,195 ) 1,380 Loss on early extinguishment of debt 7,891 — — Gain on sale of businesses (30,732 ) (16,884 ) — Interest expense, net of interest income 85,808 83,525 76,553 Income from operations before (benefit) provision for income taxes $ 58,689 $ 8,716 $ 109,646 Revenue, property, plant and equipment and intangible assets outside of the United States For the year ended December 31, 2017 , the Company generated $2,392.0 million or 81.2% of revenues in the United States and Puerto Rico, $552.1 million or 18.7% of revenues in Canada, and less than 0.1% of revenues in other international locations. For the year ended December 31, 2016 , the Company generated $2,213.4 million or 80.3% of revenues in the United States and Puerto Rico, $538.0 million or 19.5% of revenues in Canada, and less than 0.1% of revenues in other international locations. For the year ended December 31, 2015 , the Company generated $2,576.2 million or 78.7% of revenues in the United States and Puerto Rico, $695.0 million or 21.2% of revenues in Canada, and less than 0.1% of revenues in other international locations. As of December 31, 2017 , the Company had property, plant and equipment, net of depreciation and amortization of $1,587.4 million , and permits and other intangible assets of $469.1 million . Of these totals, $411.9 million or 26.0% of property, plant and equipment and $60.5 million or 12.9% of permits and other intangible assets were in Canada, with the balance being in the United States and Puerto Rico (except for insignificant assets in other foreign countries). As of December 31, 2016 , the Company had property, plant and equipment, net of depreciation and amortization of $1,611.8 million , and permits and other intangible assets of $498.7 million . Of these totals, $400.3 million or 24.8% of property, plant and equipment and $63.1 million or 12.7% of permits and other intangible assets were in Canada, with the balance being in the United States and Puerto Rico (except for insignificant assets in other foreign countries). (18) SEGMENT REPORTING (Continued) The following table presents assets by reported segment and in the aggregate (in thousands): December 31, 2017 December 31, 2016 Property, plant and equipment, net Technical Services $ 504,754 $ 521,134 Industrial and Field Services 254,091 245,143 Safety-Kleen 582,162 584,647 Oil, Gas and Lodging Services 168,294 182,038 Corporate Items 78,064 78,865 Total property, plant and equipment, net $ 1,587,365 $ 1,611,827 Goodwill and Permits and other intangibles, net Technical Services Goodwill $ 60,133 $ 61,116 Permits and other intangibles, net 73,775 78,625 Total Technical Services 133,908 139,741 Industrial and Field Services Goodwill 112,253 107,968 Permits and other intangibles, net 17,049 17,817 Total Industrial and Field Services 129,302 125,785 Safety-Kleen Goodwill 306,137 296,070 Permits and other intangibles, net 371,609 391,390 Total Safety-Kleen 677,746 687,460 Oil, Gas and Lodging Services Goodwill — — Permits and other intangibles, net 6,695 10,889 Total Oil, Gas and Lodging Services 6,695 10,889 Total $ 947,651 $ 963,875 (18) SEGMENT REPORTING (Continued) The following table presents the total assets by reported segment (in thousands): December 31, 2017 December 31, 2016 December 31, 2015 Technical Services $ 847,994 $ 862,957 $ 800,060 Industrial and Field Services 464,142 446,826 461,180 Safety-Kleen 1,471,291 1,474,755 1,297,971 Oil, Gas and Lodging Services 229,105 253,242 333,245 Corporate Items 694,038 644,140 538,972 Total $ 3,706,570 $ 3,681,920 $ 3,431,428 The following table presents the total assets by geographical area (in thousands): December 31, 2017 December 31, 2016 December 31, 2015 United States $ 2,985,394 $ 2,960,337 $ 2,575,746 Canada 721,176 721,583 851,949 Other foreign — — 3,733 Total $ 3,706,570 $ 3,681,920 $ 3,431,428

GUARANTOR AND NON-GUARANTOR SUB

GUARANTOR AND NON-GUARANTOR SUBSIDIARIES	12 Months Ended
	Dec. 31, 2017
Guarantor and Non-Guarantor Subsidiaries Financial Information [Abstract]
GUARANTOR AND NON-GUARANTOR SUBSIDIARIES	GUARANTOR AND NON-GUARANTOR SUBSIDIARIES 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”). (19) GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Continued) Following is the condensed consolidating balance sheet at December 31, 2017 (in thousands): Clean Harbors, Inc. Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Adjustments Total Assets: Cash and cash equivalents $ 51,638 $ 207,777 $ 59,984 $ — $ 319,399 Short-term marketable securities — — 38,179 — 38,179 Intercompany receivables 238,339 590,100 52,909 (881,348 ) — Accounts receivable, net — 433,042 95,882 — 528,924 Other current assets 897 233,602 52,947 (19,892 ) 267,554 Property, plant and equipment, net — 1,174,975 412,390 — 1,587,365 Investments in subsidiaries 3,112,547 569,568 — (3,682,115 ) — Intercompany debt receivable — 92,530 21,000 (113,530 ) — Goodwill — 415,641 62,882 — 478,523 Permits and other intangibles, net — 408,655 60,473 — 469,128 Other long-term assets 2,084 12,064 3,350 — 17,498 Total assets $ 3,405,505 $ 4,137,954 $ 859,996 $ (4,696,885 ) $ 3,706,570 Liabilities and Stockholders' Equity: Current liabilities $ 16,954 $ 371,135 $ 135,620 $ (19,892 ) $ 503,817 Intercompany payables 574,812 289,531 17,005 (881,348 ) — Closure, post-closure and remedial liabilities, net — 148,872 16,851 — 165,723 Long-term obligations 1,625,537 — — — 1,625,537 Intercompany debt payable — 21,000 92,530 (113,530 ) — Other long-term liabilities — 201,086 22,205 — 223,291 Total liabilities 2,217,303 1,031,624 284,211 (1,014,770 ) 2,518,368 Stockholders' equity 1,188,202 3,106,330 575,785 (3,682,115 ) 1,188,202 Total liabilities and stockholders' equity $ 3,405,505 $ 4,137,954 $ 859,996 $ (4,696,885 ) $ 3,706,570 (19) GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Continued) Following is the condensed consolidating balance sheet at December 31, 2016 (in thousands): Clean Guarantor Non-Guarantor Consolidating Total Assets: Cash and cash equivalents $ 51,417 $ 155,943 $ 99,637 $ — $ 306,997 Intercompany receivables 200,337 354,836 49,055 (604,228 ) — Accounts receivable, net — 417,029 79,197 — 496,226 Other current assets 3,096 234,408 69,257 (17,113 ) 289,648 Property, plant and equipment, net — 1,211,210 400,617 — 1,611,827 Investments in subsidiaries 2,851,571 580,124 — (3,431,695 ) — Intercompany debt receivable — 86,409 24,701 (111,110 ) — Goodwill — 412,638 52,516 — 465,154 Permits and other intangibles, net — 435,594 63,127 — 498,721 Other long-term assets 2,446 7,582 4,387 (1,068 ) 13,347 Total assets $ 3,108,867 $ 3,895,773 $ 842,494 $ (4,165,214 ) $ 3,681,920 Liabilities and Stockholders' Equity: Current liabilities $ 21,805 $ 366,831 $ 133,145 $ (17,113 ) $ 504,668 Intercompany payables 365,848 237,058 1,322 (604,228 ) — Closure, post-closure and remedial liabilities, net — 150,682 15,640 — 166,322 Long-term obligations 1,633,272 — — — 1,633,272 Intercompany debt payable 3,701 21,000 86,409 (111,110 ) — Other long-term liabilities — 275,649 18,836 (1,068 ) 293,417 Total liabilities 2,024,626 1,051,220 255,352 (733,519 ) 2,597,679 Stockholders' equity 1,084,241 2,844,553 587,142 (3,431,695 ) 1,084,241 Total liabilities and stockholders' equity $ 3,108,867 $ 3,895,773 $ 842,494 $ (4,165,214 ) $ 3,681,920 (19) GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Continued) Following is the consolidating statement of operations for the year ended December 31, 2017 (in thousands): Clean Harbors, Inc. Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Adjustments Total Revenues Service revenues $ — $ 1,870,256 $ 582,042 $ (53,648 ) $ 2,398,650 Product revenues — 492,036 66,511 (12,219 ) 546,328 Total revenues — 2,362,292 648,553 (65,867 ) 2,944,978 Cost of revenues (exclusive of items shown separately below) Service cost of revenues — 1,224,326 471,120 (53,648 ) 1,641,798 Product cost of revenues — 386,455 46,639 (12,219 ) 420,875 Total cost of revenues — 1,610,781 517,759 (65,867 ) 2,062,673 Selling, general and administrative expenses — 373,050 83,598 — 456,648 Accretion of environmental liabilities — 8,479 981 — 9,460 Depreciation and amortization — 205,034 83,388 — 288,422 Income (loss) from operations — 164,948 (37,173 ) — 127,775 Other expense, net (222 ) (5,156 ) (741 ) — (6,119 ) Loss on early extinguishment of debt (7,891 ) — — — (7,891 ) Gain on sale of business — 30,732 — — 30,732 Interest (expense) income, net (87,113 ) 1,523 (218 ) — (85,808 ) Equity in earnings of subsidiaries, net of tax 157,963 (48,683 ) — (109,280 ) — Intercompany interest income (expense) — 5,288 (5,288 ) — — Income (loss) before (benefit) provision for income taxes 62,737 148,652 (43,420 ) (109,280 ) 58,689 (Benefit) provision for income taxes (38,002 ) (10,117 ) 6,069 — (42,050 ) Net income (loss) 100,739 158,769 (49,489 ) (109,280 ) 100,739 Other comprehensive income 41,919 41,919 38,131 (80,050 ) 41,919 Comprehensive income (loss) $ 142,658 $ 200,688 $ (11,358 ) $ (189,330 ) $ 142,658 (19) GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Continued) Following is the consolidating statement of operations for the year ended December 31, 2016 (in thousands): Clean Harbors, Inc. Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Adjustments Total Revenues Service revenues $ — $ 1,747,985 $ 582,075 $ (49,251 ) $ 2,280,809 Product revenues — 410,868 73,793 (10,244 ) 474,417 Total revenues — 2,158,853 655,868 (59,495 ) 2,755,226 Cost of revenues (exclusive of items shown separately below) Service cost of revenues — 1,116,132 476,329 (49,251 ) 1,543,210 Product cost of revenues — 349,069 50,822 (10,244 ) 389,647 Total cost of revenues — 1,465,201 527,151 (59,495 ) 1,932,857 Selling, general and administrative expenses 85 341,963 79,967 — 422,015 Accretion of environmental liabilities — 9,261 916 — 10,177 Depreciation and amortization — 201,153 85,849 — 287,002 Goodwill impairment charge — — 34,013 — 34,013 (Loss) income from operations (85 ) 141,275 (72,028 ) — 69,162 Other income (expense), net — 7,713 (1,518 ) — 6,195 Gain on sale of business — 1,704 15,180 — 16,884 Interest (expense) income, net (88,984 ) 5,391 68 — (83,525 ) Equity in earnings of subsidiaries, net of tax 13,568 (80,244 ) — 66,676 — Intercompany interest income (expense) — 19,855 (19,855 ) — — (Loss) income before (benefit) provision for income taxes (75,501 ) 95,694 (78,153 ) 66,676 8,716 (Benefit) provision for income taxes (35,628 ) 82,643 1,574 — 48,589 Net (loss) income (39,873 ) 13,051 (79,727 ) 66,676 (39,873 ) Other comprehensive income 40,566 40,566 15,291 (55,857 ) 40,566 Comprehensive income (loss) $ 693 $ 53,617 $ (64,436 ) $ 10,819 $ 693 (19) GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Continued) Following is the consolidating statement of operations for the year ended December 31, 2015 (in thousands): Clean Harbors, Inc. Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Adjustments Total Revenues Service revenues $ — $ 2,111,086 $ 692,216 $ (59,030 ) $ 2,744,272 Product revenues — 458,314 83,970 (11,419 ) 530,865 Total revenues — 2,569,400 776,186 (70,449 ) 3,275,137 Cost of revenues (exclusive of items shown separately below) Service cost of revenues 5 1,415,435 542,497 (59,030 ) 1,898,907 Product cost of revenues — 410,128 59,190 (11,419 ) 457,899 Total cost of revenues 5 1,825,563 601,687 (70,449 ) 2,356,806 Selling, general and administrative expenses 101 329,069 84,994 — 414,164 Accretion of environmental liabilities — 9,209 1,193 — 10,402 Depreciation and amortization — 184,017 90,177 — 274,194 Goodwill impairment charge — 4,164 27,828 — 31,992 (Loss) income from operations (106 ) 217,378 (29,693 ) — 187,579 Other income (expense), net — 491 (1,871 ) — (1,380 ) Interest (expense) income, net (78,621 ) 1,860 208 — (76,553 ) Equity in earnings of subsidiaries, net of tax 91,339 (47,141 ) — (44,198 ) — Intercompany interest income (expense) — 23,156 (23,156 ) — — Income (loss) before (benefit) provision for income taxes 12,612 195,744 (54,512 ) (44,198 ) 109,646 (Benefit) provision for income taxes (31,490 ) 104,405 (7,371 ) — 65,544 Net income (loss) 44,102 91,339 (47,141 ) (44,198 ) 44,102 Other comprehensive loss (144,050 ) (144,050 ) (93,983 ) 238,033 (144,050 ) Comprehensive loss $ (99,948 ) $ (52,711 ) $ (141,124 ) $ 193,835 $ (99,948 ) (19) GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Continued) Following is the condensed consolidating statement of cash flows for the year ended December 31, 2017 (in thousands): Clean Harbors, Inc. Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Total Net cash from operating activities $ 16,292 $ 217,001 $ 52,405 $ — $ 285,698 Cash flows from (used in) investing activities: Additions to property, plant and equipment — (142,211 ) (24,796 ) — (167,007 ) Proceeds from sale and disposal of fixed assets — 1,979 5,145 — 7,124 Proceeds from sale of investments 376 — — — 376 Acquisitions, net of cash acquired — (11,427 ) (37,800 ) — (49,227 ) Proceeds on sale of business, net of transactional costs — 45,245 181 — 45,426 Additions to intangible assets, including costs to obtain or renew permits — (1,153 ) (464 ) — (1,617 ) Purchases of available-for-sale securities — — (38,342 ) — (38,342 ) Intercompany — (54,074 ) — 54,074 — Intercompany debt — — 3,701 (3,701 ) — Net cash from (used in) investing activities 376 (161,641 ) (92,375 ) 50,373 (203,267 ) Cash flows used in financing activities: Change in uncashed checks — (3,526 ) (2,414 ) — (5,940 ) Proceeds from exercise of stock options 46 — — — 46 Tax payments related to withholdings on vested restricted stock (3,149 ) — — — (3,149 ) Deferred financing costs paid (5,718 ) — — — (5,718 ) Repurchases of common stock (48,971 ) — — — (48,971 ) Principal payment on debt (402,000 ) — — — (402,000 ) Premium paid on early extinguishment of debt (6,028 ) — — — (6,028 ) Issuance of senior secured notes, net of discount 399,000 — — — 399,000 Intercompany 54,074 — — (54,074 ) — Intercompany debt (3,701 ) — — 3,701 — Net cash used in financing activities (16,447 ) (3,526 ) (2,414 ) (50,373 ) (72,760 ) Effect of exchange rate change on cash — — 2,731 — 2,731 Increase (decrease) in cash and cash equivalents 221 51,834 (39,653 ) — 12,402 Cash and cash equivalents, beginning of year 51,417 155,943 99,637 — 306,997 Cash and cash equivalents, end of year $ 51,638 $ 207,777 $ 59,984 $ — $ 319,399 (19) GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Continued) Following is the condensed consolidating statement of cash flows for the year ended December 31, 2016 (in thousands): Clean Harbors, Inc. Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Total Net cash from operating activities $ 51,033 $ 125,591 $ 83,000 $ — $ 259,624 Cash flows used in investing activities: Additions to property, plant and equipment — (194,184 ) (25,200 ) — (219,384 ) Proceeds from sale and disposal of fixed assets — 12,926 7,891 — 20,817 Proceeds on sale of business, net of transactional costs — 18,885 28,249 — 47,134 Acquisitions, net of cash acquired — (196,915 ) (10,000 ) — (206,915 ) Additions to intangible assets, including costs to obtain or renew permits — (1,749 ) (1,082 ) — (2,831 ) Purchases of available-for-sale securities (102 ) — (496 ) — (598 ) Investment in subsidiaries (257,125 ) — — 257,125 — Intercompany — (23,182 ) — 23,182 — Intercompany debt — 63,118 (21,000 ) (42,118 ) — Net cash used in investing activities (257,227 ) (321,101 ) (21,638 ) 238,189 (361,777 ) Cash flows from (used in) financing activities: Change in uncashed checks — (3,651 ) 474 — (3,177 ) Proceeds from exercise of stock options 627 — — — 627 Tax payments related to withholdings on vested restricted stock (2,819 ) — — — (2,819 ) Repurchases of common stock (22,188 ) — — — (22,188 ) Excess tax benefit of stock-based compensation 1,198 — — — 1,198 Issuance of senior unsecured notes, including premium 250,625 250,625 — (250,625 ) 250,625 Intercompany 23,182 — 6,500 (29,682 ) — Deferred financing cost paid (4,031 ) — — — (4,031 ) Intercompany debt — 21,000 (63,118 ) 42,118 — Net cash from (used in) financing activities 246,594 267,974 (56,144 ) (238,189 ) 220,235 Effect of exchange rate change on cash — — 4,207 — 4,207 Increase in cash and cash equivalents 40,400 72,464 9,425 — 122,289 Cash and cash equivalents, beginning of year 11,017 83,479 90,212 — 184,708 Cash and cash equivalents, end of year $ 51,417 $ 155,943 $ 99,637 $ — $ 306,997 (19) GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Continued) Following is the condensed consolidating statement of cash flows for the year ended December 31, 2015 (in thousands): Clean Harbors, Inc. Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Total Net cash from operating activities $ 9,543 $ 314,585 $ 72,255 $ — $ 396,383 Cash flows used in investing activities: Additions to property, plant and equipment — (220,789 ) (36,407 ) — (257,196 ) Proceeds from sales and disposal of fixed assets — 1,447 4,748 — 6,195 Acquisitions, net of cash acquired — (94,345 ) — — (94,345 ) Additions to intangible assets including costs to obtain or renew permits — — (5,296 ) — (5,296 ) Intercompany — (75,506 ) — 75,506 — Intercompany debt — 14,272 — (14,272 ) — Net cash used in investing activities — (374,921 ) (36,955 ) 61,234 (350,642 ) Cash flows from (used in) financing activities: Change in uncashed checks — (10,129 ) (4,501 ) — (14,630 ) Proceeds from exercise of stock options 397 — — — 397 Tax payments related to withholdings on vested restricted stock (2,159 ) — — — (2,159 ) Repurchases of common stock (73,347 ) — — — (73,347 ) Payments of capital leases — (203 ) (308 ) — (511 ) Excess tax benefit of stock-based compensation 71 — — — 71 Intercompany 75,506 — — (75,506 ) — Intercompany debt — — (14,272 ) 14,272 — Net cash from (used in) financing activities 468 (10,332 ) (19,081 ) (61,234 ) (90,179 ) Effect of exchange rate change on cash — — (17,733 ) — (17,733 ) Increase (decrease) in cash and cash equivalents 10,011 (70,668 ) (1,514 ) — (62,171 ) Cash and cash equivalents, beginning of year 1,006 154,147 91,726 — 246,879 Cash and cash equivalents, end of year $ 11,017 $ 83,479 $ 90,212 $ — $ 184,708

QUARTERLY DATA (UNAUDITED)

QUARTERLY DATA (UNAUDITED)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
QUARTERLY DATA (UNAUDITED)	QUARTERLY DATA (UNAUDITED) First Quarter Second Quarter Third Quarter Fourth Quarter (in thousands except per share amounts) 2017 Revenues $ 688,941 $ 752,788 $ 755,846 $ 747,403 Cost of revenues (1) 496,585 519,803 519,595 526,690 Income from operations 5,433 46,744 47,663 27,935 Other expense, net (1,549 ) (833 ) (432 ) (3,305 ) Net (loss) income (2) (21,393 ) 25,880 12,058 84,194 Basic (loss) earnings per share (3) (0.37 ) 0.45 0.21 1.48 Diluted (loss) earnings per share (3) (0.37 ) 0.45 0.21 1.48 First Quarter Second Quarter Third Quarter Fourth Quarter (in thousands except per share amounts) 2016 Revenues $ 636,083 $ 697,510 $ 729,520 $ 692,113 Cost of revenues (1) 464,279 480,002 491,915 496,661 (Loss) income from operations (4) (4,087 ) 34,504 16,802 21,943 Other (expense) income, net (350 ) (189 ) (198 ) 6,932 Net (loss) income (2) (20,871 ) 3,966 (10,255 ) (12,713 ) Basic (loss) earnings per share (3) (0.36 ) 0.07 (0.18 ) (0.22 ) Diluted (loss) earnings per share (3) (0.36 ) 0.07 (0.18 ) (0.22 ) ______________________________________ (1) Items shown separately on the statements of operations consist of (i) accretion of environmental liabilities and (ii) depreciation and amortization. (2) The second quarter of 2017 net income includes a $31.7 million pre-tax gain on the sale of a non-core line of business within the Company's Technical Services segment and a $6.0 million loss on early extinguishment of debt. The third quarter of 2017 net income had a $1.9 million loss on early extinguishment of debt. As a result of the Tax Act, the fourth quarter of 2017 net income includes a $93.0 million tax benefit related to a reduction of the Company's net deferred tax liability. The third quarter of 2016 net loss includes a $16.4 million pre-tax gain on the sale of a non-core line of business within the Company's Industrial and Field Services segment. (3) (Loss) earnings per share are computed independently for each of the quarters presented. Accordingly, the quarterly basic and diluted (loss) earnings per share may not equal the total computed for the year. (4) The third quarter of 2016 results include a $34.0 million goodwill impairment charge in the Company's Lodging Services reporting unit.

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	12 Months Ended
	Dec. 31, 2017
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	SUBSEQUENT EVENTS On February 23, 2018, the Company completed the acquisition of the U.S. Industrial Cleaning Division of Veolia Environmental Services North America LLC for a purchase price of approximately $120.0 million , subject to customary closing adjustments. Due to the timing of the acquisition, preliminary opening balance sheet amounts and purchase accounting adjustments are still being prepared. The acquisition will provide significant scale and industrial services capabilities while increasing the size of the Company's existing U.S. Industrial Services business.

SCHEDULE II VALUATION AND QUALI

SCHEDULE II VALUATION AND QUALIFYING ACCOUNTS	12 Months Ended
	Dec. 31, 2017
Valuation and Qualifying Accounts [Abstract]
SCHEDULE II VALUATION AND QUALIFYING ACCOUNTS	SCHEDULE II VALUATION AND QUALIFYING ACCOUNTS For the Three Years Ended December 31, 2017 (in thousands) Allowance for Doubtful Accounts Balance Beginning of Period Additions Charged to Operating Expense Deductions from Reserves(a) Balance End of Period 2015 $ 13,476 $ 4,793 $ 3,075 $ 15,194 2016 $ 15,194 $ 6,907 $ 7,055 $ 15,046 2017 $ 15,046 $ 7,901 $ 6,774 $ 16,173 ________________________________________ (a) Amounts deemed uncollectible, net of recoveries. Revenue Allowance(b) Balance Beginning of Period Additions Charged to Revenue Deductions from Reserves Balance End of Period 2015 $ 12,185 $ 28,312 $ 24,265 $ 16,232 2016 $ 16,232 $ 24,252 $ 26,281 $ 14,203 2017 $ 14,203 $ 24,862 $ 27,439 $ 11,626 ________________________________________ (b) Due to the nature of the Company's businesses and the invoices that result from the services provided, customers may withhold payments and attempt to renegotiate amounts invoiced. In addition, for some of the services provided, the Company's invoices are based on quotes that can either generate credits or debits when the actual revenue amount is known. Based on industry knowledge and historical trends, the Company records a revenue allowance accordingly. This practice causes the volume of activity flowing through the revenue allowance during the year to be higher than the balance at the end of the year. Increases in overall sales volumes and the expansion of the customer base in recent years have also increased the volume of additions and deductions to the allowance during the year. The revenue allowance is intended to cover the net amount of revenue adjustments that may need to be credited to customers' accounts in future periods. Management determines the appropriate total revenue allowance by evaluating the following factors on a customer-by-customer basis as well as on a consolidated level: trends in adjustments to previously billed amounts, existing economic conditions and other information as deemed applicable. Revenue allowance estimates can differ materially from the actual adjustments, but historically the revenue allowance has been sufficient to cover the net amount of the reserve adjustments issued in subsequent reporting periods. Valuation Allowance on Deferred Tax Assets Balance Beginning of Period Additions Charged to Income Tax Expense Other Changes to Reserves Balance End of Period 2015 $ 29,061 $ 2,274 $ (419 ) $ 30,916 2016 $ 30,916 $ 22,564 $ 1,709 $ 55,189 2017 $ 55,189 $ 9,052 $ 4,114 $ 68,355

SIGNIFICANT ACCOUNTING POLICI33

SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation The accompanying consolidated statements include the accounts of Clean Harbors, Inc. and its majority-owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions, which are evaluated on an ongoing basis, that affect the amounts reported in the Company's consolidated financial statements and accompanying notes. Management bases its estimates on historical experience and on various other assumptions it believes to be reasonable at the time under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities and disclosure, if any, of contingent assets and liabilities and reported amounts of revenues and expenses. Actual results could differ from those estimates and judgments.
Fair Value Measurements	Fair Value Measurements The Company defines fair value as the price that would be received to sell an asset or be paid to transfer a liability in an orderly transaction between market participants at the measurement date. The Company applies the following fair value hierarchy, which prioritizes the inputs used to measure fair value into three levels and bases the categorization within the hierarchy upon the lowest level of input that is available and significant to the fair value measurement. Level 1 inputs are quoted prices in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date. Level 2 utilizes quoted market prices in markets that are not active, broker or dealer quotations, or alternative pricing sources with reasonable levels of price transparency. Level 3 inputs are unobservable inputs for the asset or liability in which there is little, if any, market activity for the asset or liability at the measurement date. The Company's financial instruments consist of cash, marketable securities, accounts and unbilled receivable, accounts payable, accrued liabilities and long-term debt obligations. Due to the short-term nature of these instruments, with the exception of long-term debt obligations and marketable securities, their estimated fair value approximates carrying value. Senior unsecured notes are recorded at par.
Cash and Uncashed Checks	Cash and Uncashed Checks Cash consists primarily of cash on deposit and money market accounts. The Company's cash management program with its revolving credit lender allows for the maintenance of a zero balance in the U.S. bank disbursement accounts that are used to issue vendor and payroll checks. The program can result in checks outstanding in excess of bank balances in the disbursement accounts. When checks are presented to the bank for payment, cash deposits in amounts sufficient to fund the checks are made, at the Company's discretion, either from funds provided by other accounts or under the terms of the Company's revolving credit facility. Therefore, until checks are presented for payment, there is no right of offset by the bank and the Company continues to have control over cash relating to both released as well as unreleased checks. Checks that have been written to vendors or employees but have not yet been presented for payment at the Company's bank are classified as uncashed checks as part of accounts payable.
Marketable Securities	Marketable Securities Marketable securities with maturities of three months or less from the date of purchase are classified as cash equivalents. Marketable securities with original maturities greater than three months from purchase date and remaining maturities less than one year are classified as short-term marketable securities. Marketable securities with remaining maturities greater than one year as of the balance sheet date and which the Company intends to hold for greater than one year, are classified as long-term marketable securities. The Company has classified its marketable securities as available-for-sale and, accordingly, carries such securities at fair value. Unrealized gains and losses are reported, net of tax, as a component of other comprehensive income (loss).
Allowances for Doubtful Accounts	Allowances for Doubtful Accounts On a regular basis, the Company evaluates its accounts receivable and establishes the allowance for doubtful accounts based on an evaluation of certain criteria and evidence of collection certainty including historical collection trends, current economic trends and changes in customer payment patterns. Past-due receivable balances are written off when the Company's internal collection efforts have been deemed unsuccessful in collecting the outstanding balance due.
Credit Concentration	Credit Concentration Concentration of credit risks in accounts receivable is limited due to the large number of customers comprising the Company's customer base throughout North America. The Company maintains policies over credit extension that include credit evaluations, credit limits and collection monitoring procedures on a customer-by-customer basis. However, the Company generally does not require collateral before services are performed. As of December 31, 2017 and 2016 , no individual customer accounted for more than 10% of accounts receivable. During each of the years ended December 31, 2017 , 2016 and 2015 , no individual customer accounted for more than 10% of total revenues.
Unbilled Receivables	Unbilled Receivables The Company recognizes unbilled accounts receivable for service and disposal transactions rendered but not invoiced to the customer as of the end of the period.
Deferred Costs Relating to Deferred Revenue	Deferred Costs Commissions and other incremental direct costs, primarily costs of materials and transportation costs, relating to deferred revenue from the Company’s parts cleaning and waste services are capitalized and deferred. The deferred costs are included in current assets in the consolidated balance sheet and charged to expense when the related revenues are recognized.
Inventories and Supplies	Inventories and Supplies Inventories are stated at the lower of cost or market. The cost of oil and oil products is principally determined on a first-in, first-out ("FIFO") basis. The cost of supplies and drums, solvent and solution and other inventories is determined on a FIFO or a weighted average cost basis. Costs for oil and oil products, solvent and repair parts include purchase costs, fleet and fuel (2) SIGNIFICANT ACCOUNTING POLICIES (Continued) costs, direct labor, transportation costs and production related costs. The Company continually reviews its inventories for obsolete or unsalable items and adjusts its carrying value to reflect estimated realizable values.
Prepaid Expenses and Other Current Assets	Prepaid Expenses and Other Current Assets Prepaid expenses and other current assets consist primarily of prepayments for various services, refundable deposits, and income taxes receivable.
Property, Plant and Equipment (excluding landfill assets)	Property, Plant and Equipment (excluding landfill assets) Property, plant and equipment are stated at cost and include amounts capitalized under capital lease obligations. Expenditures for major renewals and improvements which extend the life or usefulness of the asset are capitalized. Items of an ordinary repair or maintenance nature are charged directly to operating expense as incurred. During the construction and development period of an asset, the costs incurred, including applicable interest costs, are classified as construction-in-progress. The Company depreciates and amortizes the cost of these assets, using the straight-line method as follows: Asset Classification Estimated Useful Life Buildings and building improvements Buildings 30–42 years Leasehold and building improvements 2–45 years Camp equipment 8–15 years Vehicles 3–15 years Equipment Capitalized software and computer equipment 3–5 years Solar equipment 30 years Containers and railcars 15–20 years All other equipment 8–25 years Furniture and fixtures 5–8 years Leasehold and building improvements have a weighted average life of 9.6 years. Camp equipment consists of industrial lodging facilities that are utilized to provide lodging services to downstream oil and gas companies in Western Canada. Solar equipment consists of a solar array that is used to provide electric power for a continuously operating groundwater decontamination pump and treatment system at a closed and capped landfill located in New Jersey. The Company recognizes an impairment in the carrying value of long-lived assets when the expected future undiscounted cash flows derived from the assets, or group of assets, are less than their carrying value. For the years ended December 31, 2017 , 2016 and 2015 , the Company did not record impairment charges related to long-lived assets. The Company will continue to assess all of its long-lived assets for impairment as necessary.
Goodwill	Goodwill Goodwill is comprised of the purchase price of business acquisitions in excess of the fair value assigned at acquisition to the net tangible and identifiable intangible assets acquired. Goodwill is not amortized but is reviewed for impairment annually as of December 31, or when events or changes in the business environment indicate that the carrying value of the reporting unit may exceed its fair value, by comparing the fair value of each reporting unit to its carrying value, including goodwill. Upon adoption of Accounting Standards Update (“ASU”) 2017-04 in the fourth quarter of 2017, if the fair value is less than the carrying amount, a loss will be recorded for the excess of the carrying value of the goodwill over the implied value of the goodwill. Prior to adoption of ASU 2017-04, if the fair value was less than the carrying amount, a Step II goodwill impairment test was performed to determine if goodwill was impaired. The loss, if any, was measured as the excess of the carrying value of the goodwill over the implied value of the goodwill. See Note 7, "Goodwill and Other Intangible Assets," for additional (2) SIGNIFICANT ACCOUNTING POLICIES (Continued) information related to the Company's goodwill impairment tests and the goodwill impairment charges recorded in 2016 and 2015.
Permits and Other Intangibles	Permits and other intangibles Permits and intangible assets, such as legal fees, site surveys, engineering costs and other expenditures are recorded at cost. Other intangible assets consist primarily of customer and supplier relationships, trademarks and trade names, and non-compete agreements. Permits relating to landfills are amortized on a units-of-consumption basis. All other permits are amortized over periods ranging from 5 to 30 years on a straight-line basis. Other intangible assets are amortized on a straight-line basis over their respective useful lives, which range from 2 to 20 years. Finite-lived intangible assets are reviewed for impairment whenever events or changes in circumstances indicate that their carrying value may not be entirely recoverable. When such factors and circumstances exist, management compares the projected undiscounted future cash flows associated with the related asset or group of assets over their estimated useful lives against their respective carrying amounts. The impairment loss, if any, is measured as the excess of the carrying amount over the fair value of the asset or group of assets. Indefinite-lived intangible assets are not amortized but are reviewed for impairment annually as of December 31, or when events or changes in the business environment indicate that the carrying value may be impaired. If the fair value of the asset is less than the carrying amount, the Company performs a quantitative test to determine the fair value. The impairment loss, if any, is measured as the excess of the carrying value of the asset over its fair value. The fair value of the indefinite-lived intangible assets exceeded their carrying values at December 31, 2017 and 2016 .
Leases	Leases The Company leases rolling stock, rail cars, equipment, real estate and office equipment under operating leases. Certain real estate leases contain rent holidays and rent escalation clauses. Most of the Company's real estate lease agreements include renewal periods at the Company's option. For its operating leases, the Company recognizes rent holiday periods and scheduled rent increases on a straight-line basis over the lease term beginning with the date the Company takes possession of the leased assets.
Landfill Accounting	Landfill Accounting The Company amortizes landfill improvements and certain landfill-related permits over their estimated useful lives. The units-of-consumption method is used to amortize land, landfill cell construction, asset retirement costs and remaining landfill cells and sites. The Company also utilizes the units-of-consumption method to record closure and post-closure obligations for landfill cells and sites. Under the units-of-consumption method, the Company includes future estimated construction and asset retirement costs, as well as costs incurred to date, in the amortization base of the landfill assets. Additionally, where appropriate, as described below, the Company includes probable expansion airspace that has yet to be permitted in the calculation of the total remaining useful life of the landfill. If it is determined that expansion capacity should no longer be considered in calculating the recoverability of a landfill asset, the Company may be required to recognize an asset impairment or incur significantly higher amortization expense. If at any time the Company makes the decision to abandon the expansion effort, the capitalized costs related to the expansion effort are expensed immediately. Landfill assets —Landfill assets include the costs of landfill site acquisition, permits and cell construction incurred to date. These amounts are recorded at cost, which includes capitalized interest as applicable. Landfill assets, net of amortization, are combined with management's estimate of the costs required to complete construction of the landfill to determine the amount to be amortized over the remaining estimated useful economic life of a site. Amortization of landfill assets is recorded on a units-of-consumption basis, such that the landfill assets should be completely amortized at the date the landfill ceases accepting waste. Amortization totaled $9.5 million , $9.7 million and $11.2 million for the years ended December 31, 2017 , 2016 and 2015 , respectively. Changes in estimated costs to complete construction are applied prospectively to the amortization rate. Landfill capacity —Landfill capacity, which is the basis for the amortization of landfill assets and for the accrual of final closure and post-closure obligations, represents total permitted airspace plus unpermitted airspace that management believes is probable of ultimately being permitted based on established criteria. The Company applies the following criteria for evaluating the probability of obtaining a permit for future expansion airspace at existing sites, which provides management a basis to evaluate the likelihood of success of unpermitted expansions: (2) SIGNIFICANT ACCOUNTING POLICIES (Continued) • Personnel are actively working to obtain the permit or permit modifications (land use, state, provincial and federal) necessary for expansion of an existing landfill, and progress is being made on the project. • Management expects to submit the application within the next year and to receive all necessary approvals to accept waste within the next 5 years. • At the time the expansion is included in the Company's estimate of the landfill's useful economic life, it is probable that the required approvals will be received within the normal application and processing time periods for approvals in the jurisdiction in which the landfill is located. • The Company or other owner of the landfill has a legal right to use or obtain the right to use the land associated with the expansion plan. • There are no significant known political, technical, legal or business restrictions or issues that could impair the success of such expansion. • A financial feasibility analysis has been completed and the results demonstrate that the expansion will have a positive financial and operational impact such that management is committed to pursuing the expansion. • Additional airspace and related additional costs, including permitting, final closure and post-closure costs, have been estimated based on the conceptual design of the proposed expansion. As of December 31, 2017 , there were two unpermitted expansions at two locations included in the Company's landfill accounting model, which represented 18.4% of the Company's remaining airspace at that date. If actual expansion airspace is significantly different from the Company's estimate of expansion airspace, the amortization rates used for the units-of-consumption method would change, therefore impacting the Company's profitability. If the Company determines that there is less actual expansion airspace at a landfill, this would increase amortization expense recorded and decrease profitability, while if the Company determines a landfill has more actual expansion airspace, amortization expense would decrease and profitability would increase. As of December 31, 2017 , the Company had 11 active landfill sites (including the Company's two non-commercial landfills), which have estimated remaining lives (based on anticipated waste volumes and remaining highly probable airspace) as follows: Remaining Lives (Years) Remaining Highly Probable Airspace (cubic yards) (in thousands) Facility Name Location Permitted Unpermitted Total Altair Texas 3 438 — 438 Buttonwillow California 20 6,459 — 6,459 Deer Park Texas 5 198 — 198 Deer Trail Colorado 33 1,812 — 1,812 Grassy Mountain Utah 59 291 4,830 5,121 Kimball Nebraska 8 211 — 211 Lambton Ontario 53 4,882 — 4,882 Lone Mountain Oklahoma 24 4,402 — 4,402 Ryley Alberta 8 351 880 1,231 Sawyer North Dakota 84 3,627 — 3,627 Westmorland California 64 2,732 — 2,732 25,403 5,710 31,113 At December 31, 2017 and 2016 , the Company had no cubic yards of permitted, but not highly probable, airspace. (2) SIGNIFICANT ACCOUNTING POLICIES (Continued) The following table presents the remaining highly probable airspace from January 1, 2015 through December 31, 2017 (in thousands of cubic yards): 2017 2016 2015 Remaining capacity at January 1, 32,228 29,786 30,544 Addition of highly probable airspace, net — 3,464 516 Consumed (1,115 ) (1,022 ) (1,274 ) Remaining capacity at December 31, 31,113 32,228 29,786 Amortization of cell construction costs and accrual of cell closure obligations —Landfills are typically comprised of a number of cells, which are constructed within a defined acreage (or footprint). The cells are typically discrete units, which require both separate construction and separate capping and closure procedures. Cell construction costs are the costs required to excavate and construct the landfill cell. These costs are typically amortized on a units-of-consumption basis, such that they are completely amortized when the specific cell ceases accepting waste. In some instances, the Company has landfills that are engineered and constructed as "progressive trenches." In progressive trench landfills, a number of contiguous cells form a progressive trench. In those instances, the Company amortizes cell construction costs over the airspace within the entire trench, such that the cell construction costs will be fully amortized at the end of the trench useful life. The design and construction of a landfill does not create a landfill asset retirement obligation. Rather, the asset retirement obligation for cell closure (the cost associated with capping each cell) is incurred in relatively small increments as waste is placed in the landfill. Therefore, the cost required to construct the cell cap is capitalized as an asset retirement cost and a liability of an equal amount is established, based on the discounted cash flow associated with each capping event, as airspace is consumed. Spending for cell capping is reflected as environmental expenditures within operating activities in the statement of cash flows. Landfill final closure and post-closure liabilities —The balance of landfill final closure and post-closure liabilities at December 31, 2017 and 2016 was $32.4 million and $30.6 million , respectively. The Company has material financial commitments for the costs associated with requirements of the Environmental Protection Agency ("EPA") and the comparable regulatory agency in Canada for landfill final closure and post-closure activities. In the United States, the landfill final closure and post-closure requirements are established under the standards of the EPA, and are implemented and applied on a state-by-state basis. The Company develops estimates for the cost of these activities based on an evaluation of site-specific facts and circumstances, including the Company's interpretation of current regulatory requirements and proposed regulatory changes. Such estimates may change in the future due to various circumstances including, but not limited to, permit modifications, changes in legislation or regulations, technological changes and results of environmental studies. Final closure costs are the costs incurred after the site ceases to accept waste, but before the landfill is certified as closed by the applicable state regulatory agency. These costs generally include the costs required to cap the final cell of the landfill (if not included in cell closure), the costs required to dismantle certain structures for landfills and other landfill improvements, and regulation-mandated groundwater monitoring, and leachate management. Post-closure costs involve the maintenance and monitoring of a landfill site that has been certified closed by the applicable regulatory agency. These costs generally include groundwater monitoring and leachate management. Regulatory post-closure periods are generally 30 years after landfill closure. Final closure and post-closure obligations are accrued on a units-of-consumption basis, such that the present value of the final closure and post-closure obligations are fully accrued at the date the landfill discontinues accepting waste. Cell closure, final closure and post-closure costs (also referred to as "asset retirement obligations") are calculated by estimating the total obligation in current dollars, adjusted for inflation ( 1.02% during 2017 and 2016 ) and discounted at the Company's credit-adjusted risk-free interest rate ( 6.32% and 6.23% during 2017 and 2016 , respectively.)
Non-Landfill Closure and Post-Closure Liabilities	Non-Landfill Closure and Post-Closure Liabilities Non-landfill closure costs include costs required to dismantle and decontaminate certain structures and other costs incurred during the closure process. Post-closure costs, if required, include associated maintenance and monitoring costs as required by the closure permit. Post-closure periods are performance-based and are not generally specified in terms of years in the closure permit, but generally range from 10 to 30 years or more. (2) SIGNIFICANT ACCOUNTING POLICIES (Continued) The Company records its non-landfill closure and post-closure liability by: (i) estimating the current cost of closing a non-landfill facility and the post-closure care of that facility, if required, based upon the closure plan that the Company is required to follow under its operating permit, or in the event the facility operates with a permit that does not contain a closure plan, based upon legally enforceable closure commitments made by the Company to various governmental agencies; (ii) using probability scenarios as to when in the future operations may cease; (iii) inflating the current cost of closing the non-landfill facility on a probability weighted basis using the inflation rate to the time of closing under each probability scenario; and (iv) discounting the future value of each closing scenario back to the present using the credit-adjusted risk-free interest rate. Non-landfill closure and post-closure obligations arise when the Company commences operations. The balance of non-landfill closure and post-closure liabilities at December 31, 2017 and 2016 was $28.6 million and $27.7 million , respectively. The estimates for non-landfill closure and post-closure liabilities are inherently uncertain due to the possibility that permit and regulatory requirements will change in the future, impacting the estimation of total costs and the timing of the expenditures. Management reviews non-landfill closure and post-closure liabilities for changes to key assumptions that would impact the amount of the recorded liabilities. Changes that would prompt management to revise a liability estimate include changes in legal requirements that impact the Company's expected closure plan or scope of work, in the market price of a significant cost item, in the probability scenarios as to when future operations at a location might cease, or in the expected timing of the cost expenditures. Changes in estimates for non-landfill closure and post-closure events immediately impact the required liability and the value of the corresponding asset. If a change is made to a fully-consumed asset, the adjustment is charged immediately to expense. When a change in estimate relates to an asset that has not been fully consumed, the adjustment to the asset recognized in income prospectively as a component of amortization. Historically, material changes to non-landfill closure and post-closure estimates have been infrequent.
Remedial Liabilities	Remedial Liabilities The balance of remedial liabilities at December 31, 2017 and 2016 was $124.5 million and $128.0 million , respectively. Remedial liabilities, including Superfund liabilities, include the costs of removal or containment of contaminated material, treatment of potentially contaminated groundwater and maintenance and monitoring costs necessary to comply with regulatory requirements. Most of the Company's remedial liabilities relate to the active and inactive hazardous waste treatment and disposal facilities which the Company acquired in the last 15 years and 35 Superfund sites owned by third parties for which the Company agreed to indemnify certain remedial liabilities owed or potentially owed to governmental entities by the sellers of certain assets (the "CSD assets") which the Company acquired in 2002. The Company performed extensive due diligence to estimate accurately the aggregate liability for remedial liabilities to which the Company became potentially liable as a result of the acquisitions. The Company's estimate of remedial liabilities involved an analysis of such factors as: (i) the nature and extent of environmental contamination (if any); (ii) the terms of applicable permits and agreements with regulatory authorities as to cleanup procedures and whether modifications to such permits and agreements will likely need to be negotiated; (iii) the cost of performing anticipated cleanup activities based upon current technology; and (iv) in the case of Superfund and other sites where other parties will also be responsible for a portion of the cleanup costs, the likely allocation of such costs and the ability of such other parties to pay their share. Remedial liabilities and on-going operations are reviewed quarterly and adjustments are made as necessary. The Company periodically evaluates potential remedial liabilities at sites that it owns or operates or to which the Company or the sellers of the CSD assets (or the respective predecessors of the Company or such sellers) transported or disposed of waste, including 129 Superfund sites as of December 31, 2017 . The Company periodically reviews and evaluates sites requiring remediation, including Superfund sites, giving consideration to the nature (i.e., owner, operator, arranger, transporter or generator) and the extent (i.e., amount and nature of waste hauled to the location, number of years of site operations or other relevant factors) of the Company's (or such sellers') alleged connection with the site, the extent (if any) to which the Company believes it may have an obligation to indemnify cleanup costs in connection with the site, the regulatory context surrounding the site, the accuracy and strength of evidence connecting the Company (or such sellers) to the location, the number, connection and financial ability of other named and unnamed potentially responsible parties ("PRPs") and the nature and estimated cost of the likely remedy. Where the Company concludes that it is probable that a liability has been incurred and an amount can be estimated, a provision is made, based upon management's judgment and prior experience, of such estimated liability. Remedial liabilities are inherently difficult to estimate. Estimating remedial liabilities requires that the existing environmental contamination be understood. There are risks that the actual quantities of contaminants differ from the results of the site investigation, and that contaminants exist that have not been identified by the site investigation. In addition, the amount (2) SIGNIFICANT ACCOUNTING POLICIES (Continued) of remedial liabilities recorded is dependent on the remedial method selected. There is a risk that funds will be expended on a remedial solution that is not successful, which could result in the additional incremental costs of an alternative solution. Such estimates, which are subject to change, are subsequently revised if and when additional or new information becomes available. Remedial liabilities are discounted only when the timing of the payments is determinable and the amounts are estimable. Management's experience has been that the timing of payments for remedial liabilities is not usually estimable, and therefore the amounts of remedial liabilities are not generally discounted. In the case of remedial liabilities assumed in connection with acquisitions, acquired liabilities are recorded at fair value as of the dates of the acquisitions calculated by inflating costs in current dollars using an estimate of future inflation rates as of the respective acquisition dates until the expected time of payment, and then discounting the amount of the payments to their present value using a risk-free discount rate as of the acquisition dates. Discounts have been and will be applied to the remedial liabilities as follows: • Remedial liabilities assumed relating to acquisitions are and will continue to be inflated using the inflation rates at the time of each acquisition (ranging from 1.01% to 2.57% ) until the expected time of payment, then discounted at the risk-free interest rate at the time of such acquisition (ranging from 1.37% to 5.99% ). • Remedial liabilities incurred subsequent to the acquisitions and remedial liabilities of the Company that existed prior to the acquisitions have been and will continue to be recorded at the estimated current value of the liabilities, which is usually neither increased for inflation nor reduced for discounting.
Foreign Currency	Foreign Currency During the years ended December 31, 2017 and 2016 , the Company had operations in Canada, and to a much lesser extent, Mexico, Trinidad and India. The functional currencies of those operations are their local currency and therefore assets and liabilities of those foreign operations are translated to U.S. dollars at the exchange rate in effect at the balance sheet date and revenue and expenses at the average exchange rate for the period. Gains and losses from the translation of the consolidated financial statements of foreign subsidiaries into U.S. dollars are included in stockholders' equity as a component of accumulated other comprehensive loss. Gains and losses resulting from foreign currency transactions are recognized in the consolidated statements of operations. Recorded balances that are denominated in a currency other than the functional currency are remeasured to the functional currency using the exchange rate at the balance sheet date and gains or losses are recorded in the statements of operations. As part of the Company’s overall capital structure, intercompany loans have been established between subsidiaries of the Company and in some cases are denominated in Canadian dollars. These intercompany loans are considered to be of a long-term investment nature as the repayment of these loans is neither planned nor anticipated in the foreseeable future. Impacts from the remeasurement of these loan amounts from the Canadian to the U.S. dollar reporting currency are recorded as an adjustment to foreign currency translation adjustment within accumulated other comprehensive loss, a component of shareholders' equity.
Revenue Recognition and Deferred Revenue	Revenue Recognition and Deferred Revenue In 2017 , the Company generated services and product revenues through the following operating segments: Technical Services, Industrial Services, Field Services, Safety-Kleen, Oil and Gas Field Services, and Lodging Services. The Company recognizes revenue when persuasive evidence of an arrangement exists, delivery has occurred or services have been rendered, the price is fixed or determinable, and collection is reasonably assured. In many cases revenue is recognized net of estimated allowances. Revenue is 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. Due to the nature of the Company's business and the invoices that result from the services provided, customers may withhold payments and attempt to negotiate amounts invoiced. Accordingly, management establishes a revenue allowance to cover the estimated amounts of revenue that may need to be credited to customers' accounts in future periods. The Company records a provision for revenue allowances based on specific review of particular customers, historical trends and other relevant information. Technical Services revenue is generated from fees charged for hazardous material management and disposal services including onsite environmental management services, collection and transportation, packaging, recycling, treatment and disposal of hazardous and non-hazardous waste. Services are provided based on purchase orders or agreements with the (2) SIGNIFICANT ACCOUNTING POLICIES (Continued) customer and include prices based upon units of volume of waste, and transportation and other fees. Collection and transportation, and packaging revenues are recognized when the transported waste is received at the disposal facility. Revenues for treatment and disposal of hazardous waste are recognized upon completion of wastewater treatment, final disposition in a landfill or incineration of the waste, all at Company-owned sites, or when the waste is shipped to a third party for processing and disposal. Revenues from recycled oil are recognized upon shipment to the customer. Revenue for all other Technical Services is recognized when services are rendered. The Company, at the request of a customer, periodically enters into bundled arrangements for the collection and transportation and disposal of waste. The Company accounts for such arrangements as multiple-element arrangements with each substantive deliverable treated as a separate unit of accounting. The Company measures and allocates the consideration from the arrangement to the separate units, based on evidence of the estimated selling price for each deliverable. 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. Industrial Services provides industrial and specialty services, such as high-pressure and chemical cleaning, daylighting services, production servicing, decoking, pigging and material processing to refineries, chemical plants, oil sands facilities, pulp and paper mills, and other industrial facilities. 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. Revenues are recognized over the term of the agreements or as services are performed. Field Services provides cleanup services on customer sites or other locations on a scheduled or emergency response basis. These services are provided based on purchase orders or agreements with the customers and include prices based upon daily, hourly or job rates for equipment, materials and personnel. Revenues are recorded as services are performed. Revenue is recognized on contracts with retainage when services have been rendered and collectability is reasonably assured. Safety-Kleen service revenues are generated from providing parts cleaning services, containerized waste services, oil collection services, blending and packaging of blended oils, and other complementary services. Product revenues consist of sales of high quality base and blended lubricating oils manufactured from re-refining used oil and sales of recycled used oil collected in excess of the Company's re-refining capacity into recycled fuel oil. The high quality base and blended lubricating oils are sold to third-party distributors, retailers, government agencies, fleets, railroads and industrial customers. In 2016, the Company implemented a direct-to-consumer sales model for Safety-Kleen’s renewable oil products. The recycled fuel oil is sold to asphalt plants, industrial plants, blenders, pulp and paper companies, vacuum gas oil producers and marine diesel oil producers. Product revenue is recognized upon the transfer of title. Parts cleaning services generally consist of placing a specially designed parts washer at a customer's premises and then, on a recurring basis, delivering clean solvent or aqueous-based washing fluid, cleaning and servicing the parts washer and removing the used solvent or aqueous fluid. The Company also services customer-owned parts washers. Revenue from parts cleaning services is recognized over the service interval. Service intervals represent the actual amount of time between service visits to a particular parts cleaning customer. Average service intervals vary from seven to 14 weeks depending on several factors, such as customer accommodation, types of machines serviced and frequency of use. Containerized waste services consist of profiling, collecting, transporting and recycling or disposing of a wide variety of hazardous and non-hazardous wastes. Collection and transportation, and packaging revenues are recognized when the transported waste is received at the disposal facility. Other complementary products and services include vacuum services, sale of allied supply products and other environmental services. Revenue is recognized when products are delivered and services are performed. Oil and Gas Field Services provides fluid handling, fluid hauling, surface rentals, seismic services, and directional boring services to the energy sector serving oil and gas exploration and production and power generation. 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. Revenues for such services are recognized over the term of the agreements or as services are performed. Oil and Gas Field Services also provides equipment rentals to support drill sites. Revenue from rentals is recognized ratably over the rental period. Lodging Services provides accommodation services, along with catering and hospitality primarily in remote areas of Western Canada. In addition, within Lodging Services is a manufacturing unit that provides construction of modular buildings including modular camp accommodations and wastewater solutions. Revenue for lodging and related services is recognized in the period each room is used by the customer based on the related lodging agreements. Revenue for manufacturing services is recognized based on contracted terms resulting in either a percentage of completion methodology or upon transfer of ownership of completed units. (2) SIGNIFICANT ACCOUNTING POLICIES (Continued) For all periods presented, any amounts billed to customers related to shipping and handling are classified as revenue and the Company's shipping and handling costs are included in costs of revenues. In the course of the Company's operations, it collects sales tax from its customers and recognizes a current liability which is then relieved when the taxes are remitted to the appropriate governmental authorities. The Company excludes the sales tax collected from its revenues.
Advertising Expense	Advertising Expense Advertising costs are expensed as incurred
Stock-Based Compensation	Stock-Based Compensation Stock-based compensation cost is measured at the grant date based on the fair value of the award and is recognized as expense over the requisite service period, which generally represents the vesting period, and includes an estimate of awards that will be forfeited. In addition, the Company issues awards with performance targets which are recognized as expense over the requisite service period when management believes it is probable those targets will be achieved. The fair value of the Company's grants of restricted stock are based on the quoted market price for the Company's common stock on the respective dates of grant. Compensation expense is based on the number of awards expected to vest. Forfeitures estimated when recognizing compensation expense are adjusted when actual forfeitures differ from the estimate.
Income Taxes	Income Taxes There are two major components of income tax expense, current and deferred. Current income tax expense approximates cash to be paid or refunded for taxes for the applicable period. Deferred tax expense or benefit is the result of changes between deferred tax assets and liabilities. Deferred tax assets and liabilities are determined based upon the temporary differences between the financial statement basis and tax basis of assets and liabilities as well as from net operating loss and tax credit carryforwards as measured by the enacted tax rates, which will be in effect when these differences reverse. The effect of a change in tax rates on deferred tax assets and liabilities is generally recognized in income in the period that includes the enactment date. See Note 12, "Income Taxes," for more information related to the Tax Cuts and Jobs Act of 2017 and its impacts. The Company evaluates the recoverability of future tax deductions and credits and a valuation allowance is established by tax jurisdiction when, based on an evaluation of both positive and negative objective verifiable evidence, it is more likely than not that some portion or all of deferred tax assets will not be realized. The Company recognizes and measures a tax benefit from uncertain tax positions when it is more likely than not that the tax position will be sustained on examination by the taxing authorities, based on the technical merits of the position. The Company recognizes a liability for unrecognized tax benefits resulting from uncertain tax positions taken or expected to be taken in a tax return. The Company adjusts these liabilities when its judgment changes as a result of the evaluation of new information not previously available. Due to the complexity of some of these uncertainties, the ultimate resolution may result in a payment that is materially different from the current estimate or future recognition of an unrecognized benefit. These differences will be reflected as increases or decreases to income tax expense in the period in which they are determined. The Company recognizes interest and penalties related to unrecognized tax benefits within the income tax expense line in the consolidated statements of operations. Accrued interest and penalties are included within deferred taxes, unrecognized tax benefits and other long-term liabilities line in the consolidated balance sheet
Earnings per Share	Earnings per Share ("EPS") Basic EPS is calculated by dividing income available to common stockholders by the weighted average number of common shares outstanding during the period. Diluted EPS gives effect to all potentially dilutive common shares that were outstanding during the period
Business Combinations	Business Combinations For all business combinations, the Company records 100% of all assets and liabilities of the acquired business, including goodwill, at their estimated fair values. Acquisition-related costs are expensed in the period in which the costs are incurred and the services are received
New Accounting Pronouncements	Recent Accounting Pronouncements Standards implemented In July 2015, the Financial Accounting Standards Board (“FASB”) issued ASU 2015-11, Inventory (Topic 330) . The amendment provides guidance regarding the measurement of inventory. Entities should measure inventory within the scope of this update at the lower of cost and net realizable value. The adoption of ASU 2015-11 was applied prospectively and as of January 1, 2017 did not have an impact on the Company's consolidated financial statements. In March 2016, the FASB issued ASU 2016-09, Compensation-Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting . The amendment simplifies several aspects of the accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities and classification on the statement of cash flows. Stock-based compensation excess tax benefits or deficiencies are now reflected in the consolidated statements of operations as a component of the (benefit) provision for income taxes, whereas they previously were recognized in equity. Additionally, the consolidated statements of cash flows now include excess tax benefits as an operating activity. Previously, income tax benefits at settlement of an award were reported as a reduction to operating cash flows and an increase to financing cash flows to the extent that those benefits exceeded the income tax benefits reported in earnings during the award's vesting period. The Company has elected to apply that change in cash flow classification on a prospective basis, leaving previously reported net cash from operating activities and net cash from financing activities in the accompanying consolidated statement of cash flows for the prior periods unchanged. Finally, the Company has elected to account for forfeitures as they occur, rather than estimate expected forfeitures. As a result of the adoption of this update, the Company recorded a cumulative-effect adjustment that reduced beginning retained earnings by $0.5 million , net of tax. In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments (a consensus of the Emerging Issues Task Force) . The amendment provides updated guidance on eight specific cash flow issues, including debt prepayment or debt extinguishment costs, settlement of zero-coupon debt instruments, contingent consideration payments made after a business combination, proceeds from settlement of insurance claims and corporate-owned life insurance, distributions received from equity method investees, beneficial interests in securitization transactions and separately identifiable cash flows and application of the predominance principle. The Company early adopted the amendment on a retrospective basis in the second quarter of fiscal year 2017. As a result of adoption, the Company has recorded cash paid in 2017 for debt prepayment and extinguishment costs as financing activities in the accompanying consolidated statements of cash flows. In January 2017, FASB issued ASU 2017-04, Intangibles - Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment . The amendment simplifies the subsequent measurement of goodwill by eliminating Step 2 from the goodwill impairment test. The Company early adopted ASU 2017-04 for its 2017 annual goodwill impairment test. Adoption did not have an impact on the Company's consolidated financial statements. On December 22, 2017, the SEC staff issued Staff Accounting Bulletin 118 (SAB 118), which provides guidance on accounting for the tax effects of the Tax Cuts and Jobs Act (the “Tax Act”). SAB 118 provides a measurement period that should not extend beyond one year from the enactment date for companies to complete the accounting under Accounting Standards Codification (ASC) 740. In accordance with SAB 118, a company must reflect the income tax effects of those aspects of the Tax Act for which the accounting under ASC 740 is complete. To the extent that a company’s accounting for certain income tax effects of the Tax Act is incomplete but for which they are able to determine a reasonable estimate, it must record a provisional amount in the financial statements. Provisional treatment is proper in light of anticipated additional guidance from various taxing authorities, the SEC, the FASB, and even the Joint Committee on Taxation. If a company cannot determine a provisional amount to be included in the financial statements, it should continue to apply ASC 740 on the basis of the provisions of the tax laws that were in effect immediately before the enactment of the Tax Act. In February 2018, the FASB issued ASU 2018-02, Income Statement-Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income . The amendment allows a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Act and also requires certain disclosures about stranded tax effects. The Company early adopted ASU 2018-02 as part of its fiscal year 2017 consolidated financial statements. Adoption did not have a material impact on the Company's consolidated financial statements. (2) SIGNIFICANT ACCOUNTING POLICIES (Continued) Standards to be implemented The Company is currently evaluating the impact that the below standards to be implemented will have on the Company's consolidated financial statements. In May 2014, FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) . ASU 2014-09 outlines a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry-specific guidance. In August 2015, FASB issued ASU 2015-14 which deferred the effective date of ASU 2014-09 for all entities by one year. In March 2016, FASB issued ASU 2016-08, which reduces the potential for diversity in practice arising from inconsistent application of the principal versus agent guidance, as well as the cost and complexity of applying Topic 606 both at transition and on an ongoing basis. In April 2016, FASB issued ASU 2016-10, which reduces the potential for diversity in initial application, as well as the cost and complexity of applying Topic 606 both at transition and on an ongoing basis. In May 2016, FASB issued ASU 2016-12, which provided narrow scope improvements and practical expedients on assessing collectability, presentation of sales taxes, noncash consideration, and completed contracts and contract modifications at transition. ASU 2014-09 is effective for annual reporting periods (including interim reporting periods within those periods) beginning after December 15, 2017. 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). The Company adopted ASU 2014‑09 as of January 1, 2018 using the modified retrospective method. The Company has reached conclusions on key accounting assessments related to the new standard and the adoption of the new standard did not have a material impact to its consolidated financial statement results and is not expected to be material going forward. The Company expects revenue recognition for its portfolio of services and products to remain largely unchanged 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 January 2016, FASB issued ASU 2016-01, Financial Instruments - Overall (Subtopic 825-10) . The amendment provides guidance to enhance the reporting model for financial instruments to provide users of financial statements with more decision-useful information. The amendment in this update is effective for fiscal years beginning after December 15, 2018, and interim periods within fiscal years beginning after December 15, 2019. Adoption is not expected to have a material impact on the Company's consolidated financial statements. In February 2016, FASB issued ASU 2016-02, Leases (Topic 842) . The amendment increases transparency and comparability among organizations by recognizing lease assets and lease liabilities on the balance sheet and disclosing key information about leasing arrangements. The amendment is effective for annual reporting periods (including interim reporting periods within those periods) beginning after December 15, 2018, with early adoption permitted. The Company expects to 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 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 amendment should be applied using a modified retrospective basis and is effective for annual reporting periods (including interim reporting periods within those periods) beginning after December 15, 2017. Adoption is not expected to have a material impact on the Company's consolidated financial statements. In January 2017, FASB issued ASU 2017-01, Business Combinations (Topic 805): Clarifying the Definition of a Business . The amendments in this Update provide a more robust framework to use in determining when a set of assets and activities is a business. The amendments in this Update should be applied prospectively and are effective for annual reporting periods (including interim reporting periods within those periods) beginning after December 15, 2017. Adoption is not expected to have a material impact on the Company's consolidated financial statements. (2) SIGNIFICANT ACCOUNTING POLICIES (Continued) In February 2017, the FASB issued ASU 2017-05, Other Income-Gains and Losses from the Derecognition of Nonfinancial Assets (Subtopic 610-20): Clarifying the Scope of Asset Derecognition Guidance and Accounting for Partial Sales of Nonfinancial Assets . The amendment is meant to clarify the scope of ASC Subtopic 610-20, Other Income-Gains and Losses from the Derecognition of Nonfinancial Assets and to add guidance for partial sales of nonfinancial assets. The amendment should be applied using a full retrospective method or a modified retrospective method and is effective at the same time as ASU 2014-09. Further, the Company is required to adopt ASU 2017-05 at the same time that it adopts the guidance in ASU 2014-09. Adoption is not expected to have a material impact on the Company's consolidated financial statements. 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 amendment is effective for the Company for annual and interim reporting periods after December 15, 2017. The amendment should be applied retrospectively for the presentation of the service cost component and the other components of net periodic pension cost and net periodic postretirement benefit cost in the income statement and prospectively, on and after the effective date, for the capitalization of the service cost component of net periodic pension cost and net periodic postretirement benefit in assets. The Company is currently evaluating the impact ASU 2017-07 will have on its consolidated financial statements. In May 2017, the FASB issued ASU 2017-09, Compensation-Stock Compensation (Topic 718): Scope of Modification Accounting . The amendment is meant to provide guidance about which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting in Topic 718. The amendment should be applied prospectively to an award modified on or after the adoption date and is effective for annual reporting periods (including interim reporting periods within those periods) beginning after December 15, 2017.

SIGNIFICANT ACCOUNTING POLICI34

SIGNIFICANT ACCOUNTING POLICIES (Tables)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Available-for-sale Securities	Available-for-sale investments were as follows (in thousands): December 31, 2017 Amortized Cost Gross Unrealized Loss Gross Unrealized Gain Fair Value Commercial paper $ 2,048 $ — $ — $ 2,048 Total cash equivalents 2,048 — — 2,048 U.S. Treasury securities 3,865 (10 ) — 3,855 Corporate notes and bonds 32,790 (61 ) — 32,729 Commercial paper 1,595 — — 1,595 Total short-term marketable securities 38,250 (71 ) — 38,179 Total financial assets $ 40,298 $ (71 ) $ — $ 40,227
Marketable Securities	Marketable securities by contractual maturity as of December 31, 2017 are shown below (in thousands). Amortized Cost Fair Value Due in one year or less $ 18,684 $ 18,670 After one year through three years 21,614 21,557 Total financial assets $ 40,298 $ 40,227
Fair Value, Assets Measured on Recurring Basis	Financial assets measured and recorded at fair value on a recurring basis consisted of the following types of instruments (in thousands): December 31, 2017 Level 1 Level 2 Level 3 Total Commercial paper $ — $ 2,048 $ — $ 2,048 Total cash equivalents — 2,048 — 2,048 U.S. Treasury securities 3,855 — — 3,855 Corporate notes and bonds — 32,729 — 32,729 Commercial paper — 1,595 — 1,595 Total short-term marketable securities 3,855 34,324 — 38,179 Total financial assets $ 3,855 $ 36,372 $ — $ 40,227
Schedule of Asset Classification and Estimated Useful Life	The Company depreciates and amortizes the cost of these assets, using the straight-line method as follows: Asset Classification Estimated Useful Life Buildings and building improvements Buildings 30–42 years Leasehold and building improvements 2–45 years Camp equipment 8–15 years Vehicles 3–15 years Equipment Capitalized software and computer equipment 3–5 years Solar equipment 30 years Containers and railcars 15–20 years All other equipment 8–25 years Furniture and fixtures 5–8 years Property, plant and equipment consisted of the following (in thousands): December 31, 2017 December 31, 2016 Land $ 121,658 $ 120,575 Asset retirement costs (non-landfill) 14,593 14,567 Landfill assets 144,539 139,708 Buildings and improvements 414,384 373,160 Camp equipment 170,012 152,740 Vehicles 617,959 541,022 Equipment 1,644,102 1,483,736 Furniture and fixtures 5,708 5,492 Construction in progress 57,618 146,904 3,190,573 2,977,904 Less - accumulated depreciation and amortization 1,603,208 1,366,077 Total property, plant and equipment, net $ 1,587,365 $ 1,611,827
Schedule of Active Landfill Sites	As of December 31, 2017 , the Company had 11 active landfill sites (including the Company's two non-commercial landfills), which have estimated remaining lives (based on anticipated waste volumes and remaining highly probable airspace) as follows: Remaining Lives (Years) Remaining Highly Probable Airspace (cubic yards) (in thousands) Facility Name Location Permitted Unpermitted Total Altair Texas 3 438 — 438 Buttonwillow California 20 6,459 — 6,459 Deer Park Texas 5 198 — 198 Deer Trail Colorado 33 1,812 — 1,812 Grassy Mountain Utah 59 291 4,830 5,121 Kimball Nebraska 8 211 — 211 Lambton Ontario 53 4,882 — 4,882 Lone Mountain Oklahoma 24 4,402 — 4,402 Ryley Alberta 8 351 880 1,231 Sawyer North Dakota 84 3,627 — 3,627 Westmorland California 64 2,732 — 2,732 25,403 5,710 31,113
Remaining Highly Probable Airspace	The following table presents the remaining highly probable airspace from January 1, 2015 through December 31, 2017 (in thousands of cubic yards): 2017 2016 2015 Remaining capacity at January 1, 32,228 29,786 30,544 Addition of highly probable airspace, net — 3,464 516 Consumed (1,115 ) (1,022 ) (1,274 ) Remaining capacity at December 31, 31,113 32,228 29,786

BUSINESS COMBINATIONS (Tables)

BUSINESS COMBINATIONS (Tables)	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Summary of Allocation of Purchase Price	The components and preliminary allocation of the purchase price consist of the following amounts (in thousands): At Acquisition Dates As Reported Measurement Period Adjustments Final Allocation Accounts receivable $ 15,767 $ 475 $ 16,242 Inventories and supplies 12,515 173 12,688 Prepaid expenses and other current assets 777 (25 ) 752 Property, plant and equipment 143,025 891 143,916 Permits and other intangibles 28,856 — 28,856 Current liabilities (20,258 ) 353 (19,905 ) Closure and post-closure liabilities, less current portion (2,408 ) (596 ) (3,004 ) Remedial liabilities, less current portion (2,041 ) (504 ) (2,545 ) Deferred taxes, unrecognized tax benefits and other long-term liabilities (17,019 ) (3,200 ) (20,219 ) Total identifiable net assets 159,214 (2,433 ) 156,781 Goodwill 45,791 2,186 47,977 Total purchase price, net of cash acquired $ 205,005 $ (247 ) $ 204,758 The allocation of the purchase price was based on estimates of the fair value of assets acquired and liabilities assumed as of April 11, 2015 . The Company believes that such information provides a reasonable basis for estimating the fair values of assets acquired and liabilities assumed. The Company finalized the purchase accounting for the acquisition of TFI in the second quarter of 2016. Preliminary Allocations as reported at December 31, 2015 Measurement Period Adjustments Final Allocations Accounts Receivable $ 7,585 $ (284 ) $ 7,301 Inventories and supplies 1,791 — 1,791 Prepaid expenses and other current assets 665 — 665 Property, plant and equipment 28,862 (1,221 ) 27,641 Permits and other intangibles 18,100 — 18,100 Current liabilities (5,845 ) (39 ) (5,884 ) Closure and post-closure liabilities (1,676 ) (657 ) (2,333 ) Deferred taxes, unrecognized tax benefits and other long-term liabilities (10,030 ) 856 (9,174 ) Total identifiable net assets 39,452 (1,345 ) 38,107 Goodwill 39,134 2,095 41,229 Total $ 78,586 $ 750 $ 79,336

DISPOSITION OF BUSINESS (Tables

DISPOSITION OF BUSINESS (Tables)	12 Months Ended
	Dec. 31, 2017
Discontinued Operations and Disposal Groups [Abstract]
Disposition of Business	The following table presents the carrying amounts of the Company's Transformer Services business that was disposed of on June 30, 2017 (in thousands): June 30, 2017 Total current assets $ 7,241 Property, plant and equipment, net 8,773 Total other assets 1,681 Total assets divested $ 17,695 Total current liabilities 3,849 Total other liabilities 1,170 Total liabilities divested $ 5,019 Net carrying value divested $ 12,676 The following table presents the carrying amounts of the Company's Catalyst Services business immediately preceding the disposition on September 1, 2016 (in thousands): September 1, 2016 Total current assets $ 19,019 Property, plant and equipment, net 11,154 Total other assets 6,500 Total assets divested $ 36,673 Total current liabilities 4,040 Total other liabilities 566 Total liabilities divested $ 4,606 Net carrying value divested $ 32,067 The following table presents income attributable to the Transformer Services business included in the Company's consolidated results of operations for each of the periods shown and through its disposition on June 30, 2017 (in thousands): For the years ended December 31, 2017 2016 2015 Income before (benefit) provision for income taxes $ 2,771 $ 4,187 $ 3,597 The following table presents income attributable to the Catalyst Services business included in the Company's consolidated results of operations for each of the periods shown and through its disposition on September 1, 2016 (in thousands): For the years ended December 31, 2016 2015 Income before (benefit) provision for income taxes $ 290 $ 2,520

INVENTORIES AND SUPPLIES (Table

INVENTORIES AND SUPPLIES (Tables)	12 Months Ended
	Dec. 31, 2017
Inventory Disclosure [Abstract]
Schedule of Inventory	Inventories and supplies consisted of the following (in thousands): December 31, 2017 December 31, 2016 Oil and oil related products $ 58,142 $ 52,158 Supplies and drums 94,242 90,610 Solvent and solutions 9,167 8,566 Modular camp accommodations 1,826 15,255 Other 12,635 11,839 Total inventories and supplies $ 176,012 $ 178,428

PROPERTY, PLANT, AND EQUIPMENT

PROPERTY, PLANT, AND EQUIPMENT (Tables)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	The Company depreciates and amortizes the cost of these assets, using the straight-line method as follows: Asset Classification Estimated Useful Life Buildings and building improvements Buildings 30–42 years Leasehold and building improvements 2–45 years Camp equipment 8–15 years Vehicles 3–15 years Equipment Capitalized software and computer equipment 3–5 years Solar equipment 30 years Containers and railcars 15–20 years All other equipment 8–25 years Furniture and fixtures 5–8 years Property, plant and equipment consisted of the following (in thousands): December 31, 2017 December 31, 2016 Land $ 121,658 $ 120,575 Asset retirement costs (non-landfill) 14,593 14,567 Landfill assets 144,539 139,708 Buildings and improvements 414,384 373,160 Camp equipment 170,012 152,740 Vehicles 617,959 541,022 Equipment 1,644,102 1,483,736 Furniture and fixtures 5,708 5,492 Construction in progress 57,618 146,904 3,190,573 2,977,904 Less - accumulated depreciation and amortization 1,603,208 1,366,077 Total property, plant and equipment, net $ 1,587,365 $ 1,611,827

GOODWILL AND OTHER INTANGIBLE39

GOODWILL AND OTHER INTANGIBLE ASSETS (Tables)	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Changes to Goodwill	The changes in goodwill for the years ended December 31, 2017 and 2016 were as follows (in thousands): Technical Industrial Safety-Kleen Oil, Gas and Lodging Services Totals Balance at January 1, 2016 $ 49,267 $ 105,286 $ 266,344 $ 32,208 $ 453,105 Increase from current period acquisitions 12,572 6,953 26,266 — 45,791 Measurement period adjustments from prior period acquisitions — — 2,095 — 2,095 Decrease from disposition of business — (4,994 ) — — (4,994 ) Goodwill impairment charge — — — (34,013 ) (34,013 ) Foreign currency translation (723 ) 723 1,365 1,805 3,170 Balance at December 31, 2016 $ 61,116 $ 107,968 $ 296,070 $ — $ 465,154 Increase from current period acquisitions — 3,000 5,687 — 8,687 Measurement period adjustments from prior period acquisitions — — 2,186 — 2,186 Decrease from disposition of business (1,300 ) — — — (1,300 ) Foreign currency translation 317 1,285 2,194 — 3,796 Balance at December 31, 2017 $ 60,133 $ 112,253 $ 306,137 $ — $ 478,523
Schedule of Finite-Lived Intangible Assets by Major Class	As of December 31, 2017 and 2016 , the Company's finite-lived and indefinite lived intangible assets consisted of the following (in thousands): December 31, 2017 December 31, 2016 Cost Accumulated Amortization Net Cost Accumulated Amortization Net Permits $ 174,721 $ 74,347 $ 100,374 $ 171,637 $ 67,301 $ 104,336 Customer and supplier relationships 399,224 158,972 240,252 393,426 127,462 265,964 Other intangible assets 36,766 31,592 5,174 34,254 28,456 5,798 Total amortizable permits and other intangible assets 610,711 264,911 345,800 599,317 223,219 376,098 Trademarks and trade names 123,328 — 123,328 122,623 — 122,623 Total permits and other intangible assets $ 734,039 $ 264,911 $ 469,128 $ 721,940 $ 223,219 $ 498,721
Schedule of Indefinite-Lived Intangible Assets	As of December 31, 2017 and 2016 , the Company's finite-lived and indefinite lived intangible assets consisted of the following (in thousands): December 31, 2017 December 31, 2016 Cost Accumulated Amortization Net Cost Accumulated Amortization Net Permits $ 174,721 $ 74,347 $ 100,374 $ 171,637 $ 67,301 $ 104,336 Customer and supplier relationships 399,224 158,972 240,252 393,426 127,462 265,964 Other intangible assets 36,766 31,592 5,174 34,254 28,456 5,798 Total amortizable permits and other intangible assets 610,711 264,911 345,800 599,317 223,219 376,098 Trademarks and trade names 123,328 — 123,328 122,623 — 122,623 Total permits and other intangible assets $ 734,039 $ 264,911 $ 469,128 $ 721,940 $ 223,219 $ 498,721
Schedule of Expected Amortization for the Net Carrying Amount of Finite Lived Intangible Assets	The expected amortization of the net carrying amount of finite-lived intangible assets at December 31, 2017 is as follows (in thousands): Years Ending December 31, Expected Amortization 2018 $ 34,631 2019 31,684 2020 29,130 2021 26,888 2022 26,727 Thereafter 196,740 $ 345,800

ACCRUED EXPENSES (Tables)

ACCRUED EXPENSES (Tables)	12 Months Ended
	Dec. 31, 2017
Payables and Accruals [Abstract]
Accrued Expenses	Accrued expenses consisted of the following at December 31 (in thousands): December 31, 2017 December 31, 2016 Insurance $ 57,889 $ 63,061 Interest 12,660 21,536 Accrued compensation and benefits 55,861 34,641 Income, real estate, sales and other taxes 27,330 35,083 Other 34,242 36,400 $ 187,982 $ 190,721

CLOSURE AND POST-CLOSURE LIAB41

CLOSURE AND POST-CLOSURE LIABILITIES (Tables)	12 Months Ended
	Dec. 31, 2017
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, 2016 through December 31, 2017 were as follows (in thousands): Landfill Retirement Liability Non-Landfill Retirement Liability Total Balance at January 1, 2016 $ 32,023 $ 24,226 $ 56,249 Liabilities assumed in acquisitions — 2,408 2,408 Measurement period adjustments from prior period acquisitions — 657 657 New asset retirement obligations 1,983 — 1,983 Accretion 2,705 2,398 5,103 Changes in estimates recorded to statement of operations (1,415 ) (1,204 ) (2,619 ) Changes in estimates recorded to balance sheet (3,289 ) — (3,289 ) Expenditures (1,446 ) (802 ) (2,248 ) Currency translation and other 69 18 87 Balance at December 31, 2016 30,630 27,701 58,331 Liabilities assumed in acquisitions — 59 59 Measurement period adjustments from prior period acquisitions — 596 596 New asset retirement obligations 1,881 — 1,881 Adjustment related to disposition of business — (1,170 ) (1,170 ) Accretion 2,243 2,505 4,748 Changes in estimates recorded to statement of operations (131 ) (109 ) (240 ) Changes in estimates recorded to balance sheet 364 (591 ) (227 ) Expenditures (2,777 ) (448 ) (3,225 ) Currency translation and other 172 112 284 Balance at December 31, 2017 $ 32,382 $ 28,655 $ 61,037
Schedule of Expected Payments Related to Asset Retirement Obligations	Anticipated payments (based on current estimated costs and anticipated timing of necessary regulatory approvals to commence work on closure and post-closure activities) for each of the next five years and thereafter are as follows (in thousands): Year ending December 31, 2018 $ 6,313 2019 8,957 2020 12,152 2021 8,652 2022 353 Thereafter 285,404 Undiscounted closure and post-closure liabilities 321,831 Less: Discount at credit-adjusted risk-free rate (161,767 ) Less: Undiscounted estimated closure and post-closure liabilities relating to airspace not yet consumed (99,027 ) Present value of closure and post-closure liabilities $ 61,037

REMEDIAL LIABILITIES (Tables)

REMEDIAL LIABILITIES (Tables)	12 Months Ended
	Dec. 31, 2017
Environmental Remediation Obligations [Abstract]
Changes to Remedial Liabilities	The changes to remedial liabilities from January 1, 2016 through December 31, 2017 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, 2016 $ 2,327 $ 63,613 $ 66,052 $ 131,992 Liabilities assumed in acquisitions — — 2,041 2,041 Accretion 110 2,737 2,227 5,074 Changes in estimates recorded to statement of operations (538 ) 1,520 (2,617 ) (1,635 ) Expenditures (122 ) (3,893 ) (5,907 ) (9,922 ) Currency translation and other — 174 283 457 Balance at December 31, 2016 1,777 64,151 62,079 128,007 Measurement period adjustments from prior period acquisitions — — 504 504 Accretion 86 2,648 1,978 4,712 Changes in estimates recorded to statement of operations (21 ) (289 ) 355 45 Expenditures (42 ) (3,906 ) (5,792 ) (9,740 ) Currency translation and other — 2,738 (1,798 ) 940 Balance at December 31, 2017 $ 1,800 $ 65,342 $ 57,326 $ 124,468
Remedial Liabilities Anticipated Payments for Each of the Next Five Years	Anticipated payments at December 31, 2017 (based on current estimated costs and anticipated timing of necessary regulatory approvals to commence work on remedial activities) for each of the next five years and thereafter were as follows (in thousands): Year ending December 31, 2018 $ 14,507 2019 16,934 2020 15,259 2021 10,212 2022 7,566 Thereafter 83,767 Undiscounted remedial liabilities 148,245 Less: Discount (23,777 ) Total remedial liabilities $ 124,468
Environmental Exit Costs by Cost	The following tables show, respectively, (i) the amounts of such estimated liabilities associated with the types of facilities and sites involved and (ii) the amounts of such estimated liabilities associated with each facility or site which represents at least 5% of the total and with all other facilities and sites as a group and as of December 31, 2017 . (10) REMEDIAL LIABILITIES (Continued) Estimates Based on Type of Facility or Site (in thousands): Type of Facility or Site Remedial Liability % of Total Reasonably Possible Additional Liabilities(1) Facilities now used in active conduct of the Company's business (44 facilities) $ 54,193 43.5 % $ 11,747 Inactive facilities not now used in active conduct of the Company's business but most of which were acquired because the assumption of remedial liabilities for such facilities was part of the purchase price for the CSD assets (38 facilities) 62,706 50.4 10,549 Superfund sites owned by third parties (16 sites) 7,569 6.1 757 Total $ 124,468 100.0 % $ 23,053 ___________________________________ (1) Amounts represent the high end of the range of management's best estimate of the reasonably possible additional liabilities. Estimates Based on Amount of Potential Liability (in thousands): Location Type of Facility or Site Remedial Liability % of Total Reasonably Possible Additional Liabilities(1) Baton Rouge, LA(2) Closed incinerator and landfill $ 23,357 18.8 % $ 3,938 Bridgeport, NJ Closed incinerator 18,394 14.8 2,534 Mercier, Quebec(2) Idled incinerator and legal proceedings 10,414 8.4 1,105 Linden, NJ Operating solvent recycling center 7,678 6.2 825 Various(2) All other incinerators, landfills, wastewater treatment facilities and service centers (78 facilities) 57,056 45.7 13,894 Various(2) Superfund sites (each representing less than 5% of total liabilities) owned by third parties (16 sites) 7,569 6.1 757 Total $ 124,468 100.0 % $ 23,053 _________________________________ (1) Amounts represent the high end of the range of management's best estimate of the reasonably possible additional liabilities. (2) $17.9 million of the $124.5 million remedial liabilities and $1.8 million of the $23.1 million reasonably possible additional liabilities include estimates of remediation liabilities related to the legal and administrative proceedings discussed in Note 17, "Commitments and Contingencies," as well as other such estimated remedial liabilities.

FINANCING ARRANGEMENTS (Tables)

FINANCING ARRANGEMENTS (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Summary of Financing Arrangements	The following table is a summary of the Company's financing arrangements (in thousands): December 31, 2017 December 31, 2016 Senior secured Term Loan Agreement ("Term Loan Agreement") $ 4,000 $ — Current portion of long-term obligations, at carrying value $ 4,000 $ — Senior secured Term Loan Agreement due June 30, 2024 $ 394,000 $ — Senior unsecured notes, at 5.25%, due August 1, 2020 ("2020 Notes") 400,000 800,000 Senior unsecured notes, at 5.125%, due June 1, 2021 ("2021 Notes") 845,000 845,000 Long-term obligations, at par $ 1,639,000 $ 1,645,000 Unamortized debt issuance costs and premium, net $ (13,463 ) $ (11,728 ) Long-term obligations, at carrying value $ 1,625,537 $ 1,633,272
Schedule of Redemption Prices	The Company may redeem some or all of the 2021 Notes at any time upon proper notice, at the following redemption prices plus unpaid interest: Year Percentage Prior to December 1, 2018 101.281 % On or after December 1, 2018 100.000 % The Company may redeem some or all of the 2020 Notes which remain outstanding at any time upon proper notice, at the following redemption prices plus unpaid interest: Year Percentage Prior to August 1, 2018 101.313 % On or after August 1, 2018 100.000 %

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Schedule of Income before Income Tax, Domestic and Foreign	The domestic and foreign components of income before (benefit) provision for income taxes were as follows (in thousands): For the Year Ended December 31, 2017 2016 2015 Domestic $ 101,714 $ 87,328 $ 164,105 Foreign (43,025 ) (78,612 ) (54,459 ) Total $ 58,689 $ 8,716 $ 109,646
Schedule of Components of Provision for Income Taxes	The (benefit) provision for income taxes consisted of the following (in thousands): For the Year Ended December 31, 2017 2016 2015 Current: Federal $ 25,613 $ 14,798 $ 46,775 State 11,083 8,763 11,120 Foreign 4,589 9,844 5,719 41,285 33,405 63,614 Deferred Federal (85,488 ) 21,814 12,254 State 1,085 1,644 2,766 Foreign 1,068 (8,274 ) (13,090 ) (83,335 ) 15,184 1,930 (Benefit) provision for income taxes $ (42,050 ) $ 48,589 $ 65,544
Schedule of Effective Income Tax Rate Reconciliation	The effective income tax rate varied from the amount computed using the statutory federal income tax rate as follows (in thousands): For the Year Ended December 31, 2017 2016 2015 Tax expense at US statutory rate $ 20,541 $ 3,051 $ 38,376 State income taxes, net of federal benefit 4,547 6,010 8,449 Foreign rate differential 3,733 3,646 3,951 Valuation allowance 16,552 22,564 1,824 Uncertain tax position interest and penalties 3,730 107 32 Goodwill impairment — 11,905 10,974 Other 1,856 1,306 1,938 Adjustment for Tax Cuts and Jobs Act (93,009 ) — — (Benefit) provision for income taxes $ (42,050 ) $ 48,589 $ 65,544
Schedule of Deferred Tax Assets and Liabilities	The components of the total net deferred tax assets and liabilities at December 31, 2017 and 2016 were as follows (in thousands): 2017 2016 Deferred tax assets: Provision for doubtful accounts 7,417 11,189 Closure, post-closure and remedial liabilities 28,189 40,829 Accrued expenses 15,382 19,826 Accrued compensation 1,903 2,747 Net operating loss carryforwards(1) 46,650 46,752 Tax credit carryforwards(2) 17,504 25,348 Uncertain tax positions accrued interest and federal benefit 921 1,241 Stock-based compensation 2,268 1,993 Other 3,258 555 Total deferred tax assets 123,492 150,480 Deferred tax liabilities: Property, plant and equipment (144,325 ) (207,799 ) Permits and other intangible assets (107,407 ) (161,295 ) Prepaids (8,080 ) (11,030 ) Total deferred tax liabilities (259,812 ) (380,124 ) Total net deferred tax liability before valuation allowance (136,320 ) (229,644 ) Less valuation allowance (68,355 ) (55,189 ) Net deferred tax liabilities $ (204,675 ) $ (284,833 ) ___________________________________ (1) As of December 31, 2017 , the net operating loss carryforwards included (i) state net operating loss carryovers of $186.7 million which will begin to expire in 2018, (ii) federal net operating loss carryforwards of $48.0 million which will begin to expire in 2025, and (iii) foreign net operating loss carryforwards of $116.1 million which will begin to expire in 2018. (2) As of December 31, 2017 , the foreign tax credit carryforwards of $17.5 million will expire between 2020 and 2024.
Summary of Income Tax Contingencies	The changes to unrecognized tax benefits (excluding related penalties and interest) from January 1, 2015 through December 31, 2017 , were as follows (in thousands): 2017 2016 2015 Unrecognized tax benefits as of January 1 $ 1,738 $ 2,064 $ 2,537 Additions to current year tax positions 1,457 — — Additions to prior year tax positions 2,031 — — Settlements (231 ) (533 ) (217 ) Foreign currency translation 126 207 (256 ) Unrecognized tax benefits as of December 31 $ 5,121 $ 1,738 $ 2,064

EARNINGS (LOSS) PER SHARE (Tabl

EARNINGS (LOSS) PER SHARE (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Reconciliation of Basic and Diluted Earnings Per Share Computations	The following are computations of basic and diluted earnings (loss) per share (in thousands except for per share amounts): Years Ended December 31, 2017 2016 2015 Numerator for basic and diluted earnings (loss) per share: Net income (loss) $ 100,739 $ (39,873 ) $ 44,102 Denominator: Weighted basic shares outstanding 57,072 57,532 58,324 Dilutive effect of equity-based compensation awards 128 — 110 Weighted dilutive shares outstanding 57,200 57,532 58,434 Basic earnings (loss) per share $ 1.77 $ (0.69 ) $ 0.76 Diluted earnings (loss) per share $ 1.76 $ (0.69 ) $ 0.76

ACCUMULATED OTHER COMPREHENSI46

ACCUMULATED OTHER COMPREHENSIVE LOSS (Tables)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Schedule of Reclassification of Accumulated Other Comprehensive Income (Loss)	The changes in accumulated other comprehensive loss by component and related tax effects for the years ended December 31, 2017 , 2016 and 2015 were as follows (in thousands): Foreign Currency Translation Adjustments Unrealized (Losses) Gains on Available-for-Sale Securities Unfunded Pension Liability Total Balance at January 1, 2015 $ (108,889 ) $ — $ (1,953 ) $ (110,842 ) Other comprehensive loss before reclassifications (144,050 ) — (7 ) (144,057 ) Amounts reclassified out of accumulated other comprehensive loss — — — — Tax effects — — 7 7 Other comprehensive loss (144,050 ) — — (144,050 ) Balance at December 31, 2015 $ (252,939 ) $ — $ (1,953 ) $ (254,892 ) Other comprehensive income (loss) before reclassifications 23,967 (535 ) 216 23,648 Amounts reclassified out of accumulated other comprehensive loss — — — — Tax effects 16,761 214 (57 ) 16,918 Other comprehensive income (loss) 40,728 (321 ) 159 40,566 Balance at December 31, 2016 $ (212,211 ) $ (321 ) $ (1,794 ) $ (214,326 ) Other comprehensive income before reclassifications 41,636 184 146 41,966 Amounts reclassified out of accumulated other comprehensive loss — 222 — 222 Tax effects — (231 ) (38 ) (269 ) Other comprehensive income 41,636 175 108 41,919 Balance at December 31, 2017 $ (170,575 ) $ (146 ) $ (1,686 ) $ (172,407 ) The amounts reclassified out of accumulated other comprehensive loss into the consolidated statement of operations, with presentation location, during the year ended December 31, 2017 were as follows (in thousands): Other Comprehensive Income Components December 31, 2017 Location Unrealized (losses) gains on available-for-sale securities $ (222 ) Other (expense) income, net

STOCK-BASED COMPENSATION AND 47

STOCK-BASED COMPENSATION AND EMPLOYEE BENEFIT PLANS (Tables)	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of Restricted Stock	The following table summarizes information about restricted stock awards for the year ended December 31, 2017 : Restricted Stock Number of Shares Weighted Average Grant-Date Fair Value Unvested at January 1, 2017 510,041 $ 52.65 Granted 307,455 55.93 Vested (136,787 ) 53.16 Forfeited (75,776 ) 52.46 Unvested at December 31, 2017 604,933 $ 54.23
Schedule of Performance Stock Awards	The following table summarizes information about performance stock awards for the year ended December 31, 2017 : Performance Stock Number of Shares Weighted Average Grant-Date Fair Value Unvested at January 1, 2017 220,882 $ 54.69 Granted 170,897 55.87 Vested (53,096 ) 55.60 Forfeited (148,554 ) 57.14 Unvested at December 31, 2017 190,129 $ 55.63

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Lease Payments for Operating Leases	The following is a summary of future minimum payments under operating leases that have initial or remaining non-cancelable lease terms in excess of one year at December 31, 2017 (in thousands): Year Total Operating Leases 2018 $ 44,476 2019 37,161 2020 30,233 2021 22,173 2022 17,432 Thereafter 45,370 Total minimum lease payments $ 196,845
Self-Insurance Liabilities Anticipated Payments	Anticipated payments for contingencies related to workers' compensation, comprehensive general liability and vehicle liability related claims at December 31, 2017 for each of the next five years and thereafter were as follows (in thousands): Years ending December 31, 2018 $ 16,525 2019 11,259 2020 7,848 2021 4,393 2022 3,688 Thereafter 5,769 Undiscounted self-insurance liabilities 49,482 Less: Discount 1,568 Total self-insurance liabilities (included in accrued expenses) $ 47,914

SEGMENT REPORTING (Tables)

SEGMENT REPORTING (Tables)	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Reconciliation of Third Party Revenues to Direct Revenues	The following table reconciles third-party revenues to direct revenues for the years ended December 31, 2017 , 2016 and 2015 (in thousands): For the Year Ended December 31, 2017 Technical Services Industrial and Field Services Safety-Kleen Oil, Gas and Lodging Services Corporate Items Totals Third-party revenues $ 980,232 $ 631,216 $ 1,213,703 $ 117,252 $ 2,575 $ 2,944,978 Intersegment revenues, net 161,533 (37,694 ) (125,822 ) 1,983 — — Corporate Items, net 2,384 200 5 368 (2,957 ) — Direct revenues $ 1,144,149 $ 593,722 $ 1,087,886 $ 119,603 $ (382 ) $ 2,944,978 For the Year Ended December 31, 2016 Technical Services Industrial and Field Services Safety-Kleen Oil, Gas and Lodging Services Corporate Items Totals Third-party revenues $ 906,495 $ 618,245 $ 1,110,727 $ 116,692 $ 3,067 $ 2,755,226 Intersegment revenues, net 147,866 (35,724 ) (115,013 ) 2,871 — — Corporate Items, net 2,374 (306 ) 369 320 (2,757 ) — Direct revenues $ 1,056,735 $ 582,215 $ 996,083 $ 119,883 $ 310 $ 2,755,226 For the Year Ended December 31, 2015 Technical Services Industrial and Field Services Safety-Kleen Oil, Gas and Lodging Services Corporate Items Totals Third-party revenues $ 991,410 $ 1,023,638 $ 1,060,926 $ 198,705 $ 458 $ 3,275,137 Intersegment revenues, net 144,084 (32,903 ) (119,232 ) 8,051 — — Corporate Items, net 3,586 (782 ) (5 ) 383 (3,182 ) — Direct revenues $ 1,139,080 $ 989,953 $ 941,689 $ 207,139 $ (2,724 ) $ 3,275,137
Reconciliation to Consolidated Statements of Income to Adjusted EBITDA	The following table presents Adjusted EBITDA information used by management by reported segment (in thousands): For the Year Ended December 31, 2017 2016 2015 Adjusted EBITDA: Technical Services $ 276,592 $ 271,176 $ 291,737 Industrial and Field Services 43,010 51,191 161,447 Safety-Kleen 249,811 219,546 172,262 Oil, Gas and Lodging Services 1,708 (3,292 ) 11,704 Corporate Items (145,464 ) (138,267 ) (132,983 ) Total 425,657 400,354 504,167 Reconciliation to Consolidated Statements of Operations: Accretion of environmental liabilities 9,460 10,177 10,402 Depreciation and amortization 288,422 287,002 274,194 Goodwill impairment charges — 34,013 31,992 Income from operations 127,775 69,162 187,579 Other expense (income), net 6,119 (6,195 ) 1,380 Loss on early extinguishment of debt 7,891 — — Gain on sale of businesses (30,732 ) (16,884 ) — Interest expense, net of interest income 85,808 83,525 76,553 Income from operations before (benefit) provision for income taxes $ 58,689 $ 8,716 $ 109,646
PP&E and Intangible Assets by Segment	The following table presents assets by reported segment and in the aggregate (in thousands): December 31, 2017 December 31, 2016 Property, plant and equipment, net Technical Services $ 504,754 $ 521,134 Industrial and Field Services 254,091 245,143 Safety-Kleen 582,162 584,647 Oil, Gas and Lodging Services 168,294 182,038 Corporate Items 78,064 78,865 Total property, plant and equipment, net $ 1,587,365 $ 1,611,827 Goodwill and Permits and other intangibles, net Technical Services Goodwill $ 60,133 $ 61,116 Permits and other intangibles, net 73,775 78,625 Total Technical Services 133,908 139,741 Industrial and Field Services Goodwill 112,253 107,968 Permits and other intangibles, net 17,049 17,817 Total Industrial and Field Services 129,302 125,785 Safety-Kleen Goodwill 306,137 296,070 Permits and other intangibles, net 371,609 391,390 Total Safety-Kleen 677,746 687,460 Oil, Gas and Lodging Services Goodwill — — Permits and other intangibles, net 6,695 10,889 Total Oil, Gas and Lodging Services 6,695 10,889 Total $ 947,651 $ 963,875
Total Assets by Segment	The following table presents the total assets by reported segment (in thousands): December 31, 2017 December 31, 2016 December 31, 2015 Technical Services $ 847,994 $ 862,957 $ 800,060 Industrial and Field Services 464,142 446,826 461,180 Safety-Kleen 1,471,291 1,474,755 1,297,971 Oil, Gas and Lodging Services 229,105 253,242 333,245 Corporate Items 694,038 644,140 538,972 Total $ 3,706,570 $ 3,681,920 $ 3,431,428
Total Assets by Geographical Area	The following table presents the total assets by geographical area (in thousands): December 31, 2017 December 31, 2016 December 31, 2015 United States $ 2,985,394 $ 2,960,337 $ 2,575,746 Canada 721,176 721,583 851,949 Other foreign — — 3,733 Total $ 3,706,570 $ 3,681,920 $ 3,431,428

GUARANTOR AND NON-GUARANTOR S50

GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Tables)	12 Months Ended
	Dec. 31, 2017
Guarantor and Non-Guarantor Subsidiaries Financial Information [Abstract]
Schedule of Condensed Consolidating Balance Sheet	Following is the condensed consolidating balance sheet at December 31, 2017 (in thousands): Clean Harbors, Inc. Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Adjustments Total Assets: Cash and cash equivalents $ 51,638 $ 207,777 $ 59,984 $ — $ 319,399 Short-term marketable securities — — 38,179 — 38,179 Intercompany receivables 238,339 590,100 52,909 (881,348 ) — Accounts receivable, net — 433,042 95,882 — 528,924 Other current assets 897 233,602 52,947 (19,892 ) 267,554 Property, plant and equipment, net — 1,174,975 412,390 — 1,587,365 Investments in subsidiaries 3,112,547 569,568 — (3,682,115 ) — Intercompany debt receivable — 92,530 21,000 (113,530 ) — Goodwill — 415,641 62,882 — 478,523 Permits and other intangibles, net — 408,655 60,473 — 469,128 Other long-term assets 2,084 12,064 3,350 — 17,498 Total assets $ 3,405,505 $ 4,137,954 $ 859,996 $ (4,696,885 ) $ 3,706,570 Liabilities and Stockholders' Equity: Current liabilities $ 16,954 $ 371,135 $ 135,620 $ (19,892 ) $ 503,817 Intercompany payables 574,812 289,531 17,005 (881,348 ) — Closure, post-closure and remedial liabilities, net — 148,872 16,851 — 165,723 Long-term obligations 1,625,537 — — — 1,625,537 Intercompany debt payable — 21,000 92,530 (113,530 ) — Other long-term liabilities — 201,086 22,205 — 223,291 Total liabilities 2,217,303 1,031,624 284,211 (1,014,770 ) 2,518,368 Stockholders' equity 1,188,202 3,106,330 575,785 (3,682,115 ) 1,188,202 Total liabilities and stockholders' equity $ 3,405,505 $ 4,137,954 $ 859,996 $ (4,696,885 ) $ 3,706,570 (19) GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Continued) Following is the condensed consolidating balance sheet at December 31, 2016 (in thousands): Clean Guarantor Non-Guarantor Consolidating Total Assets: Cash and cash equivalents $ 51,417 $ 155,943 $ 99,637 $ — $ 306,997 Intercompany receivables 200,337 354,836 49,055 (604,228 ) — Accounts receivable, net — 417,029 79,197 — 496,226 Other current assets 3,096 234,408 69,257 (17,113 ) 289,648 Property, plant and equipment, net — 1,211,210 400,617 — 1,611,827 Investments in subsidiaries 2,851,571 580,124 — (3,431,695 ) — Intercompany debt receivable — 86,409 24,701 (111,110 ) — Goodwill — 412,638 52,516 — 465,154 Permits and other intangibles, net — 435,594 63,127 — 498,721 Other long-term assets 2,446 7,582 4,387 (1,068 ) 13,347 Total assets $ 3,108,867 $ 3,895,773 $ 842,494 $ (4,165,214 ) $ 3,681,920 Liabilities and Stockholders' Equity: Current liabilities $ 21,805 $ 366,831 $ 133,145 $ (17,113 ) $ 504,668 Intercompany payables 365,848 237,058 1,322 (604,228 ) — Closure, post-closure and remedial liabilities, net — 150,682 15,640 — 166,322 Long-term obligations 1,633,272 — — — 1,633,272 Intercompany debt payable 3,701 21,000 86,409 (111,110 ) — Other long-term liabilities — 275,649 18,836 (1,068 ) 293,417 Total liabilities 2,024,626 1,051,220 255,352 (733,519 ) 2,597,679 Stockholders' equity 1,084,241 2,844,553 587,142 (3,431,695 ) 1,084,241 Total liabilities and stockholders' equity $ 3,108,867 $ 3,895,773 $ 842,494 $ (4,165,214 ) $ 3,681,920
Schedule of Consolidating Statement of Income	Following is the consolidating statement of operations for the year ended December 31, 2017 (in thousands): Clean Harbors, Inc. Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Adjustments Total Revenues Service revenues $ — $ 1,870,256 $ 582,042 $ (53,648 ) $ 2,398,650 Product revenues — 492,036 66,511 (12,219 ) 546,328 Total revenues — 2,362,292 648,553 (65,867 ) 2,944,978 Cost of revenues (exclusive of items shown separately below) Service cost of revenues — 1,224,326 471,120 (53,648 ) 1,641,798 Product cost of revenues — 386,455 46,639 (12,219 ) 420,875 Total cost of revenues — 1,610,781 517,759 (65,867 ) 2,062,673 Selling, general and administrative expenses — 373,050 83,598 — 456,648 Accretion of environmental liabilities — 8,479 981 — 9,460 Depreciation and amortization — 205,034 83,388 — 288,422 Income (loss) from operations — 164,948 (37,173 ) — 127,775 Other expense, net (222 ) (5,156 ) (741 ) — (6,119 ) Loss on early extinguishment of debt (7,891 ) — — — (7,891 ) Gain on sale of business — 30,732 — — 30,732 Interest (expense) income, net (87,113 ) 1,523 (218 ) — (85,808 ) Equity in earnings of subsidiaries, net of tax 157,963 (48,683 ) — (109,280 ) — Intercompany interest income (expense) — 5,288 (5,288 ) — — Income (loss) before (benefit) provision for income taxes 62,737 148,652 (43,420 ) (109,280 ) 58,689 (Benefit) provision for income taxes (38,002 ) (10,117 ) 6,069 — (42,050 ) Net income (loss) 100,739 158,769 (49,489 ) (109,280 ) 100,739 Other comprehensive income 41,919 41,919 38,131 (80,050 ) 41,919 Comprehensive income (loss) $ 142,658 $ 200,688 $ (11,358 ) $ (189,330 ) $ 142,658 (19) GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Continued) Following is the consolidating statement of operations for the year ended December 31, 2016 (in thousands): Clean Harbors, Inc. Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Adjustments Total Revenues Service revenues $ — $ 1,747,985 $ 582,075 $ (49,251 ) $ 2,280,809 Product revenues — 410,868 73,793 (10,244 ) 474,417 Total revenues — 2,158,853 655,868 (59,495 ) 2,755,226 Cost of revenues (exclusive of items shown separately below) Service cost of revenues — 1,116,132 476,329 (49,251 ) 1,543,210 Product cost of revenues — 349,069 50,822 (10,244 ) 389,647 Total cost of revenues — 1,465,201 527,151 (59,495 ) 1,932,857 Selling, general and administrative expenses 85 341,963 79,967 — 422,015 Accretion of environmental liabilities — 9,261 916 — 10,177 Depreciation and amortization — 201,153 85,849 — 287,002 Goodwill impairment charge — — 34,013 — 34,013 (Loss) income from operations (85 ) 141,275 (72,028 ) — 69,162 Other income (expense), net — 7,713 (1,518 ) — 6,195 Gain on sale of business — 1,704 15,180 — 16,884 Interest (expense) income, net (88,984 ) 5,391 68 — (83,525 ) Equity in earnings of subsidiaries, net of tax 13,568 (80,244 ) — 66,676 — Intercompany interest income (expense) — 19,855 (19,855 ) — — (Loss) income before (benefit) provision for income taxes (75,501 ) 95,694 (78,153 ) 66,676 8,716 (Benefit) provision for income taxes (35,628 ) 82,643 1,574 — 48,589 Net (loss) income (39,873 ) 13,051 (79,727 ) 66,676 (39,873 ) Other comprehensive income 40,566 40,566 15,291 (55,857 ) 40,566 Comprehensive income (loss) $ 693 $ 53,617 $ (64,436 ) $ 10,819 $ 693 (19) GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Continued) Following is the consolidating statement of operations for the year ended December 31, 2015 (in thousands): Clean Harbors, Inc. Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Adjustments Total Revenues Service revenues $ — $ 2,111,086 $ 692,216 $ (59,030 ) $ 2,744,272 Product revenues — 458,314 83,970 (11,419 ) 530,865 Total revenues — 2,569,400 776,186 (70,449 ) 3,275,137 Cost of revenues (exclusive of items shown separately below) Service cost of revenues 5 1,415,435 542,497 (59,030 ) 1,898,907 Product cost of revenues — 410,128 59,190 (11,419 ) 457,899 Total cost of revenues 5 1,825,563 601,687 (70,449 ) 2,356,806 Selling, general and administrative expenses 101 329,069 84,994 — 414,164 Accretion of environmental liabilities — 9,209 1,193 — 10,402 Depreciation and amortization — 184,017 90,177 — 274,194 Goodwill impairment charge — 4,164 27,828 — 31,992 (Loss) income from operations (106 ) 217,378 (29,693 ) — 187,579 Other income (expense), net — 491 (1,871 ) — (1,380 ) Interest (expense) income, net (78,621 ) 1,860 208 — (76,553 ) Equity in earnings of subsidiaries, net of tax 91,339 (47,141 ) — (44,198 ) — Intercompany interest income (expense) — 23,156 (23,156 ) — — Income (loss) before (benefit) provision for income taxes 12,612 195,744 (54,512 ) (44,198 ) 109,646 (Benefit) provision for income taxes (31,490 ) 104,405 (7,371 ) — 65,544 Net income (loss) 44,102 91,339 (47,141 ) (44,198 ) 44,102 Other comprehensive loss (144,050 ) (144,050 ) (93,983 ) 238,033 (144,050 ) Comprehensive loss $ (99,948 ) $ (52,711 ) $ (141,124 ) $ 193,835 $ (99,948 )
Schedule of Condensed Consolidating Statement of Cash Flows	Following is the condensed consolidating statement of cash flows for the year ended December 31, 2017 (in thousands): Clean Harbors, Inc. Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Total Net cash from operating activities $ 16,292 $ 217,001 $ 52,405 $ — $ 285,698 Cash flows from (used in) investing activities: Additions to property, plant and equipment — (142,211 ) (24,796 ) — (167,007 ) Proceeds from sale and disposal of fixed assets — 1,979 5,145 — 7,124 Proceeds from sale of investments 376 — — — 376 Acquisitions, net of cash acquired — (11,427 ) (37,800 ) — (49,227 ) Proceeds on sale of business, net of transactional costs — 45,245 181 — 45,426 Additions to intangible assets, including costs to obtain or renew permits — (1,153 ) (464 ) — (1,617 ) Purchases of available-for-sale securities — — (38,342 ) — (38,342 ) Intercompany — (54,074 ) — 54,074 — Intercompany debt — — 3,701 (3,701 ) — Net cash from (used in) investing activities 376 (161,641 ) (92,375 ) 50,373 (203,267 ) Cash flows used in financing activities: Change in uncashed checks — (3,526 ) (2,414 ) — (5,940 ) Proceeds from exercise of stock options 46 — — — 46 Tax payments related to withholdings on vested restricted stock (3,149 ) — — — (3,149 ) Deferred financing costs paid (5,718 ) — — — (5,718 ) Repurchases of common stock (48,971 ) — — — (48,971 ) Principal payment on debt (402,000 ) — — — (402,000 ) Premium paid on early extinguishment of debt (6,028 ) — — — (6,028 ) Issuance of senior secured notes, net of discount 399,000 — — — 399,000 Intercompany 54,074 — — (54,074 ) — Intercompany debt (3,701 ) — — 3,701 — Net cash used in financing activities (16,447 ) (3,526 ) (2,414 ) (50,373 ) (72,760 ) Effect of exchange rate change on cash — — 2,731 — 2,731 Increase (decrease) in cash and cash equivalents 221 51,834 (39,653 ) — 12,402 Cash and cash equivalents, beginning of year 51,417 155,943 99,637 — 306,997 Cash and cash equivalents, end of year $ 51,638 $ 207,777 $ 59,984 $ — $ 319,399 (19) GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Continued) Following is the condensed consolidating statement of cash flows for the year ended December 31, 2016 (in thousands): Clean Harbors, Inc. Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Total Net cash from operating activities $ 51,033 $ 125,591 $ 83,000 $ — $ 259,624 Cash flows used in investing activities: Additions to property, plant and equipment — (194,184 ) (25,200 ) — (219,384 ) Proceeds from sale and disposal of fixed assets — 12,926 7,891 — 20,817 Proceeds on sale of business, net of transactional costs — 18,885 28,249 — 47,134 Acquisitions, net of cash acquired — (196,915 ) (10,000 ) — (206,915 ) Additions to intangible assets, including costs to obtain or renew permits — (1,749 ) (1,082 ) — (2,831 ) Purchases of available-for-sale securities (102 ) — (496 ) — (598 ) Investment in subsidiaries (257,125 ) — — 257,125 — Intercompany — (23,182 ) — 23,182 — Intercompany debt — 63,118 (21,000 ) (42,118 ) — Net cash used in investing activities (257,227 ) (321,101 ) (21,638 ) 238,189 (361,777 ) Cash flows from (used in) financing activities: Change in uncashed checks — (3,651 ) 474 — (3,177 ) Proceeds from exercise of stock options 627 — — — 627 Tax payments related to withholdings on vested restricted stock (2,819 ) — — — (2,819 ) Repurchases of common stock (22,188 ) — — — (22,188 ) Excess tax benefit of stock-based compensation 1,198 — — — 1,198 Issuance of senior unsecured notes, including premium 250,625 250,625 — (250,625 ) 250,625 Intercompany 23,182 — 6,500 (29,682 ) — Deferred financing cost paid (4,031 ) — — — (4,031 ) Intercompany debt — 21,000 (63,118 ) 42,118 — Net cash from (used in) financing activities 246,594 267,974 (56,144 ) (238,189 ) 220,235 Effect of exchange rate change on cash — — 4,207 — 4,207 Increase in cash and cash equivalents 40,400 72,464 9,425 — 122,289 Cash and cash equivalents, beginning of year 11,017 83,479 90,212 — 184,708 Cash and cash equivalents, end of year $ 51,417 $ 155,943 $ 99,637 $ — $ 306,997 (19) GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Continued) Following is the condensed consolidating statement of cash flows for the year ended December 31, 2015 (in thousands): Clean Harbors, Inc. Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Total Net cash from operating activities $ 9,543 $ 314,585 $ 72,255 $ — $ 396,383 Cash flows used in investing activities: Additions to property, plant and equipment — (220,789 ) (36,407 ) — (257,196 ) Proceeds from sales and disposal of fixed assets — 1,447 4,748 — 6,195 Acquisitions, net of cash acquired — (94,345 ) — — (94,345 ) Additions to intangible assets including costs to obtain or renew permits — — (5,296 ) — (5,296 ) Intercompany — (75,506 ) — 75,506 — Intercompany debt — 14,272 — (14,272 ) — Net cash used in investing activities — (374,921 ) (36,955 ) 61,234 (350,642 ) Cash flows from (used in) financing activities: Change in uncashed checks — (10,129 ) (4,501 ) — (14,630 ) Proceeds from exercise of stock options 397 — — — 397 Tax payments related to withholdings on vested restricted stock (2,159 ) — — — (2,159 ) Repurchases of common stock (73,347 ) — — — (73,347 ) Payments of capital leases — (203 ) (308 ) — (511 ) Excess tax benefit of stock-based compensation 71 — — — 71 Intercompany 75,506 — — (75,506 ) — Intercompany debt — — (14,272 ) 14,272 — Net cash from (used in) financing activities 468 (10,332 ) (19,081 ) (61,234 ) (90,179 ) Effect of exchange rate change on cash — — (17,733 ) — (17,733 ) Increase (decrease) in cash and cash equivalents 10,011 (70,668 ) (1,514 ) — (62,171 ) Cash and cash equivalents, beginning of year 1,006 154,147 91,726 — 246,879 Cash and cash equivalents, end of year $ 11,017 $ 83,479 $ 90,212 $ — $ 184,708

QUARTERLY DATA (UNAUDITED) (Tab

QUARTERLY DATA (UNAUDITED) (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Quarterly Data (Unaudited)	First Quarter Second Quarter Third Quarter Fourth Quarter (in thousands except per share amounts) 2017 Revenues $ 688,941 $ 752,788 $ 755,846 $ 747,403 Cost of revenues (1) 496,585 519,803 519,595 526,690 Income from operations 5,433 46,744 47,663 27,935 Other expense, net (1,549 ) (833 ) (432 ) (3,305 ) Net (loss) income (2) (21,393 ) 25,880 12,058 84,194 Basic (loss) earnings per share (3) (0.37 ) 0.45 0.21 1.48 Diluted (loss) earnings per share (3) (0.37 ) 0.45 0.21 1.48 First Quarter Second Quarter Third Quarter Fourth Quarter (in thousands except per share amounts) 2016 Revenues $ 636,083 $ 697,510 $ 729,520 $ 692,113 Cost of revenues (1) 464,279 480,002 491,915 496,661 (Loss) income from operations (4) (4,087 ) 34,504 16,802 21,943 Other (expense) income, net (350 ) (189 ) (198 ) 6,932 Net (loss) income (2) (20,871 ) 3,966 (10,255 ) (12,713 ) Basic (loss) earnings per share (3) (0.36 ) 0.07 (0.18 ) (0.22 ) Diluted (loss) earnings per share (3) (0.36 ) 0.07 (0.18 ) (0.22 ) ______________________________________ (1) Items shown separately on the statements of operations consist of (i) accretion of environmental liabilities and (ii) depreciation and amortization. (2) The second quarter of 2017 net income includes a $31.7 million pre-tax gain on the sale of a non-core line of business within the Company's Technical Services segment and a $6.0 million loss on early extinguishment of debt. The third quarter of 2017 net income had a $1.9 million loss on early extinguishment of debt. As a result of the Tax Act, the fourth quarter of 2017 net income includes a $93.0 million tax benefit related to a reduction of the Company's net deferred tax liability. The third quarter of 2016 net loss includes a $16.4 million pre-tax gain on the sale of a non-core line of business within the Company's Industrial and Field Services segment. (3) (Loss) earnings per share are computed independently for each of the quarters presented. Accordingly, the quarterly basic and diluted (loss) earnings per share may not equal the total computed for the year. (4) The third quarter of 2016 results include a $34.0 million goodwill impairment charge in the Company's Lodging Services reporting unit.

SIGNIFICANT ACCOUNTING POLICI52

SIGNIFICANT ACCOUNTING POLICIES (Available-for-sale Investments) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 40,298
Gross Unrealized Loss	(71)
Gross Unrealized Gain	0
Fair Value	40,227
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,048
Gross Unrealized Loss	0
Gross Unrealized Gain	0
Fair Value	2,048
Total cash equivalents
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,048
Gross Unrealized Loss	0
Gross Unrealized Gain	0
Fair Value	2,048
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,865
Gross Unrealized Loss	(10)
Gross Unrealized Gain	0
Fair Value	3,855
Corporate notes and bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	32,790
Gross Unrealized Loss	(61)
Gross Unrealized Gain	0
Fair Value	32,729
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,595
Gross Unrealized Loss	0
Gross Unrealized Gain	0
Fair Value	1,595
Total short-term marketable securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	38,250
Gross Unrealized Loss	(71)
Gross Unrealized Gain	0
Fair Value	$ 38,179

SIGNIFICANT ACCOUNTING POLICI53

SIGNIFICANT ACCOUNTING POLICIES (Marketable Securities by Contractual Maturity) (Details) $ in Thousands	Dec. 31, 2017USD ($)
Accounting Policies [Abstract]
Marketable securities, due in one year or less, amortized cost	$ 18,684
Marketable securities, due in one year or less, fair value	18,670
Marketable securities, after one year through three years, amortized cost	21,614
Marketable securities, after one year through three years, fair value	21,557
Amortized Cost	40,298
Fair Value	$ 40,227

SIGNIFICANT ACCOUNTING POLICI54

SIGNIFICANT ACCOUNTING POLICIES (Financial Assets Measured on a Recurring Basis) (Details) - Recurring $ in Thousands	Dec. 31, 2017USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	$ 40,227
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	3,855
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	36,372
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	0
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	2,048
Commercial paper | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	0
Commercial paper | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	2,048
Commercial paper | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	0
Total cash equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	2,048
Total cash equivalents | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	0
Total cash equivalents | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	2,048
Total cash equivalents | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	0
U.S. Treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	3,855
U.S. Treasury securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	3,855
U.S. Treasury securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	0
U.S. Treasury securities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	0
Corporate notes and bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	32,729
Corporate notes and bonds | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	0
Corporate notes and bonds | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	32,729
Corporate notes and bonds | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	0
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	1,595
Commercial paper | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	0
Commercial paper | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	1,595
Commercial paper | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	0
Total short-term marketable securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	38,179
Total short-term marketable securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	3,855
Total short-term marketable securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	34,324
Total short-term marketable securities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	$ 0

SIGNIFICANT ACCOUNTING POLICI55

SIGNIFICANT ACCOUNTING POLICIES (Cash, Cash Equivalents and Uncashed Checks) (Details)	Dec. 31, 2017USD ($)
Accounting Policies [Abstract]
Bank disbursement account balance	$ 0

SIGNIFICANT ACCOUNTING POLICI56

SIGNIFICANT ACCOUNTING POLICIES (Credit Concentration) (Details) - customer	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounts receivable
Restricted Cash and Cash Equivalents Items [Line Items]
Concentration risk benchmark	10.00%	10.00%
Concentration risk number of major customers over benchmark	0	0
Total Revenues
Restricted Cash and Cash Equivalents Items [Line Items]
Concentration risk benchmark	10.00%	10.00%	10.00%
Concentration risk number of major customers over benchmark	0	0	0

SIGNIFICANT ACCOUNTING POLICI57

SIGNIFICANT ACCOUNTING POLICIES (Property, Plant and Equipment) (Details)	12 Months Ended
	Dec. 31, 2017
Solar equipment
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	30 years
Minimum | Buildings
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	30 years
Minimum | Leasehold and building improvements
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	2 years
Minimum | Camp equipment
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	8 years
Minimum | Vehicles
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	3 years
Minimum | Capitalized software and computer equipment
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	3 years
Minimum | Containers and railcars
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	15 years
Minimum | All other equipment
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	8 years
Minimum | Furniture and fixtures
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	5 years
Maximum | Buildings
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	42 years
Maximum | Leasehold and building improvements
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	45 years
Maximum | Camp equipment
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	15 years
Maximum | Vehicles
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	15 years
Maximum | Capitalized software and computer equipment
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	5 years
Maximum | Containers and railcars
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	20 years
Maximum | All other equipment
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	25 years
Maximum | Furniture and fixtures
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	8 years
Weighted average | Leasehold and building improvements
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	9 years 219 days

SIGNIFICANT ACCOUNTING POLICI58

SIGNIFICANT ACCOUNTING POLICIES (Goodwill and Intangible Assets) (Details)	12 Months Ended
	Dec. 31, 2017
Minimum | Permits
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life	5 years
Minimum | Other intangible assets
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life	2 years
Maximum | Permits
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life	30 years
Maximum | Other intangible assets
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life	20 years

SIGNIFICANT ACCOUNTING POLICI59

SIGNIFICANT ACCOUNTING POLICIES (Landfill Accounting) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)expansionlandfill_siteservice_locationcubic_yard	Dec. 31, 2016USD ($)cubic_yard	Dec. 31, 2015USD ($)cubic_yard
Property, Plant and Equipment [Line Items]
Application approvals, acceptance period	5 years
Number of unpermitted expansions | expansion	2
Number of service locations | service_location	2
Percentage of airspace remaining	18.40%
Landfill sites | landfill_site	11
Remaining highly probable airspace	31,113,000
Permitted, but not highly probable airspace	0	0
Remaining Airspace Capacity [Roll Forward]
Remaining capacity, beginning of period (cubic yards)	32,228,000	29,786,000	30,544,000
Addition of highly probable airspace, net (cubic yards)	0	3,464,000	516,000
Consumed (cubic yards)	(1,115,000)	(1,022,000)	(1,274,000)
Remaining capacity, end of period (cubic yards)	31,113,000	32,228,000	29,786,000
Landfill final closure and post-closure liabilities | $	$ 32.4	$ 30.6
Regulatory post-closure period for landfill	30 years
Asset retirement obligations, inflation rate	1.02%	1.02%
Asset retirement obligations, risk free rate	6.32%	6.23%
Non-landfill closure and post-closure liabilities | $	$ 28.6	$ 27.7
Minimum
Remaining Airspace Capacity [Roll Forward]
Non-landfill closure and post-closure liabilities, period	10 years
Maximum
Remaining Airspace Capacity [Roll Forward]
Non-landfill closure and post-closure liabilities, period	30 years
Landfill assets
Property, Plant and Equipment [Line Items]
Amortization | $	$ 9.5	$ 9.7	$ 11.2
Non-commercial landfills
Property, Plant and Equipment [Line Items]
Landfill sites | landfill_site	2
Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	25,403,000
Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	5,710,000
Altair | Texas
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	3 years
Remaining highly probable airspace	438,000
Altair | Texas | Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	438,000
Altair | Texas | Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0
Buttonwillow | California
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	20 years
Remaining highly probable airspace	6,459,000
Buttonwillow | California | Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	6,459,000
Buttonwillow | California | Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0
Deer Park | Texas
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	5 years
Remaining highly probable airspace	198,000
Deer Park | Texas | Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	198,000
Deer Park | Texas | Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0
Deer Trail | Colorado
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	33 years
Remaining highly probable airspace	1,812,000
Deer Trail | Colorado | Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	1,812,000
Deer Trail | Colorado | Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0
Grassy Mountain | Utah
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	59 years
Remaining highly probable airspace	5,121,000
Grassy Mountain | Utah | Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	291,000
Grassy Mountain | Utah | Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	4,830,000
Kimball | Nebraska
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	8 years
Remaining highly probable airspace	211,000
Kimball | Nebraska | Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	211,000
Kimball | Nebraska | Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0
Lambton | Ontario
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	53 years
Remaining highly probable airspace	4,882,000
Lambton | Ontario | Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	4,882,000
Lambton | Ontario | Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0
Lone Mountain | Oklahoma
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	24 years
Remaining highly probable airspace	4,402,000
Lone Mountain | Oklahoma | Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	4,402,000
Lone Mountain | Oklahoma | Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0
Ryley | Alberta
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	8 years
Remaining highly probable airspace	1,231,000
Ryley | Alberta | Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	351,000
Ryley | Alberta | Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	880,000
Sawyer | North Dakota
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	84 years
Remaining highly probable airspace	3,627,000
Sawyer | North Dakota | Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	3,627,000
Sawyer | North Dakota | Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0
Westmorland | California
Property, Plant and Equipment [Line Items]
Remaining Lives (Years)	64 years
Remaining highly probable airspace	2,732,000
Westmorland | California | Permitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	2,732,000
Westmorland | California | Unpermitted
Property, Plant and Equipment [Line Items]
Remaining highly probable airspace	0

SIGNIFICANT ACCOUNTING POLICI60

SIGNIFICANT ACCOUNTING POLICIES (Remedial Liabilities) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)site	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Regulatory Liabilities [Line Items]
Remedial Liability | $	$ 124,468	$ 128,007	$ 131,992
Period of time in years over which business acquisitions have been acquired	15 years
Superfund sites owned by third parties	35
Superfund sites	129
Minimum
Regulatory Liabilities [Line Items]
Remedial liabilities at acquisition, inflation rate	1.01%
Remedial liabilities at acquisition, risk-free interest rate	1.37%
Maximum
Regulatory Liabilities [Line Items]
Remedial liabilities at acquisition, inflation rate	2.57%
Remedial liabilities at acquisition, risk-free interest rate	5.99%

SIGNIFICANT ACCOUNTING POLICI61

SIGNIFICANT ACCOUNTING POLICIES (Revenue Recognition and Deferred Revenue) (Details)	12 Months Ended
	Dec. 31, 2017
Minimum
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Service interval	49 days
Maximum
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Service interval	98 days

SIGNIFICANT ACCOUNTING POLICI62

SIGNIFICANT ACCOUNTING POLICIES (Advertising Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Advertising costs	$ 11.8	$ 10.8	$ 15

SIGNIFICANT ACCOUNTING POLICI63

SIGNIFICANT ACCOUNTING POLICIES (Recently Accounting Pronouncements) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)
ASU 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect on retained earnings, net of tax	$ 0.5

BUSINESS COMBINATIONS (2017 Acq

BUSINESS COMBINATIONS (2017 Acquisitions) (Details) CAD / shares in Units, $ in Thousands, CAD in Millions	Oct. 16, 2017USD ($)	Sep. 22, 2017USD ($)	Jul. 14, 2017CADCAD / shares	Jul. 14, 2017USD ($)	Jan. 31, 2017USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Jul. 14, 2017USD ($)
Business Acquisition [Line Items]
Goodwill amount						$ 8,687	$ 45,791
Privately Held Washing Machine Company
Business Acquisition [Line Items]
Purchase price		$ 2,100
Goodwill amount		$ 700
Lonestar
Business Acquisition [Line Items]
Goodwill amount				$ 2,900
Payments to acquire businesses			CAD 41.8	$ 33,100
Equity payout (in CAD per share) | CAD / shares			CAD 0.72
Debt assumed			CAD 21.3					$ 16,800
2017 Acquisitions
Business Acquisition [Line Items]
Purchase price	$ 4,800				$ 11,900
Goodwill amount					$ 5,000
Revenue from acquisition included in the company's result of operations						$ 14,500

BUSINESS COMBINATIONS (2016 Acq

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

BUSINESS COMBINATIONS (2016 A66

BUSINESS COMBINATIONS (2016 Acquisitions) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2015
Business Acquisition [Line Items]
Goodwill	$ 465,154	$ 478,523	$ 453,105
2016 Acquisitions
Business Acquisition [Line Items]
Accounts receivable	16,242
Accounts receivables, measurement period adjustment	475
Inventories and supplies	12,688
Inventories and supplies, measurement period adjustment	173
Prepaid expenses and other current assets	752
Prepaid expenses and other current assets, measurement period adjustment	(25)
Property, plant and equipment	143,916
Property, plant and equipment, measurement period adjustment	891
Permits and other intangibles	28,856
Permits and other intangibles, measurement period adjustment	0
Current liabilities	(19,905)
Current liabilities, measurement period adjustment	353
Closure and post-closure liabilities, less current portion	(3,004)
Closure and post-closure liabilities, less current portion, measurement period adjustment	(596)
Remedial liabilities, less current portion	(2,545)
Remedial liabilities, less current portion, measurement period adjustment	(504)
Deferred taxes, unrecognized tax benefits and other long-term liabilities	(20,219)
Deferred taxes, unrecognized tax benefits and other long-term liabilities, measurement period adjustments	(3,200)
Total identifiable net assets	156,781
Total identifiable net assets, measurement period adjustment	(2,433)
Goodwill	47,977
Goodwill, measurement period adjustment	2,186
Total purchase price, net of cash acquired	204,758
Total purchase price, net of cash acquired, measurement period adjustment	(247)
At Acquisition Dates As Reported December 31, 2016 | 2016 Acquisitions
Business Acquisition [Line Items]
Accounts receivable	15,767
Inventories and supplies	12,515
Prepaid expenses and other current assets	777
Property, plant and equipment	143,025
Permits and other intangibles	28,856
Current liabilities	(20,258)
Closure and post-closure liabilities, less current portion	(2,408)
Remedial liabilities, less current portion	(2,041)
Deferred taxes, unrecognized tax benefits and other long-term liabilities	(17,019)
Total identifiable net assets	159,214
Goodwill	45,791
Total purchase price, net of cash acquired	$ 205,005

BUSINESS COMBINATIONS (2015 Acq

BUSINESS COMBINATIONS (2015 Acquisitions Narrative) (Details) - USD ($) $ in Thousands	Apr. 11, 2015	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Goodwill amount			$ 8,687	$ 45,791
Thermo Fluids Inc.
Business Acquisition [Line Items]
Purchase price	$ 79,300
Revenue from acquisition included in the company's result of operations				$ 38,000	$ 33,800
Privately Owned Domestic Company
Business Acquisition [Line Items]
Payments to acquire businesses		$ 14,700
Goodwill amount		$ 7,400

BUSINESS COMBINATIONS (2015 A68

BUSINESS COMBINATIONS (2015 Acquisitions) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Goodwill	$ 453,105	$ 478,523	$ 465,154
Thermo Fluids Inc.
Business Acquisition [Line Items]
Accounts receivable	7,301
Accounts receivables, measurement period adjustment	(284)
Inventories and supplies	1,791
Inventories and supplies, measurement period adjustment	0
Prepaid expenses and other current assets	665
Prepaid expenses and other current assets, measurement period adjustment	0
Property, plant and equipment	27,641
Property, plant and equipment, measurement period adjustment	(1,221)
Permits and other intangibles	18,100
Permits and other intangibles, measurement period adjustment	0
Current liabilities	(5,884)
Current liabilities, measurement period adjustment	(39)
Closure and post-closure liabilities, less current portion	(2,333)
Closure and post-closure liabilities, less current portion, measurement period adjustment	(657)
Deferred taxes, unrecognized tax benefits and other long-term liabilities	(9,174)
Deferred taxes, unrecognized tax benefits and other long-term liabilities, measurement period adjustments	856
Total identifiable net assets	38,107
Total identifiable net assets, measurement period adjustment	(1,345)
Goodwill	41,229
Goodwill, measurement period adjustment	2,095
Total purchase price, net of cash acquired	79,336
Total purchase price, net of cash acquired, measurement period adjustment	750
At Acquisition Dates As Reported December 31, 2016 | Thermo Fluids Inc.
Business Acquisition [Line Items]
Accounts receivable	7,585
Inventories and supplies	1,791
Prepaid expenses and other current assets	665
Property, plant and equipment	28,862
Permits and other intangibles	18,100
Current liabilities	(5,845)
Closure and post-closure liabilities, less current portion	(1,676)
Deferred taxes, unrecognized tax benefits and other long-term liabilities	(10,030)
Total identifiable net assets	39,452
Goodwill	39,134
Total purchase price, net of cash acquired	$ 78,586

DISPOSITION OF BUSINESS (2017 D

DISPOSITION OF BUSINESS (2017 Disposition Narrative) (Details) - Transformer Services - Disposal Group, Disposed of by Sale, Not Discontinued Operations - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale	$ 45.5
Proceeds from sale, net of transactional related costs	43.4
Transition costs	$ 2.1
Pre-tax gain		$ 30.7

DISPOSITION OF BUSINESS (201770

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

DISPOSITION OF BUSINESS DISPOSI

DISPOSITION OF BUSINESS DISPOSITION OF BUSINESS (Income (Loss) Attributable to Transformer Services) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
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 (benefit) provision for income taxes	$ 2,771	$ 4,187	$ 3,597

DISPOSITION OF BUSINESS (2016 D

DISPOSITION OF BUSINESS (2016 Disposition Narrative) (Details) - Catalyst Services - Disposal Group, Disposed of by Sale, Not Discontinued Operations - USD ($) $ in Millions	Sep. 01, 2016	Dec. 31, 2016	Mar. 31, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale	$ 50.6		$ 2
Proceeds from sale, net of cash divested	$ 49.2
Pre-tax gain		$ 16.9
Transition costs		$ 1.6

DISPOSITION OF BUSINESS (201673

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

DISPOSITION OF BUSINESS (Income

DISPOSITION OF BUSINESS (Income (Loss) Attributable to Catalyst Services) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Catalyst Services | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income before (benefit) provision for income taxes	$ 290	$ 2,520

INVENTORIES AND SUPPLIES (Detai

INVENTORIES AND SUPPLIES (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Inventory Disclosure [Abstract]
Oil and oil related products		$ 58,142	$ 52,158
Supplies and drums		94,242	90,610
Solvent and solutions		9,167	8,566
Modular camp accommodations		1,826	15,255
Other		12,635	11,839
Total inventories and supplies		176,012	178,428
Transfer of inventory to property, plant and equipment	$ 12,600	$ 12,641	$ 0	$ 0

PROPERTY, PLANT, AND EQUIPMEN76

PROPERTY, PLANT, AND EQUIPMENT (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 3,190,573	$ 2,977,904
Less - accumulated depreciation and amortization	1,603,208	1,366,077
Total property, plant and equipment, net	1,587,365	1,611,827
Interest capitalization	600	5,500	$ 2,000
Depreciation inclusive of landfill amortization	251,400	247,000	$ 234,000
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	121,658	120,575
Asset retirement costs (non-landfill)
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	14,593	14,567
Landfill assets
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	144,539	139,708
Buildings and improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	414,384	373,160
Camp equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	170,012	152,740
Vehicles
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	617,959	541,022
Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,644,102	1,483,736
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	5,708	5,492
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 57,618	$ 146,904

GOODWILL AND OTHER INTANGIBLE77

GOODWILL AND OTHER INTANGIBLE ASSETS (Changes to Goodwill) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Roll Forward]
Goodwill, beginning of period		$ 465,154	$ 453,105
Increase from current period acquisitions		8,687	45,791
Measurement period adjustments from prior period acquisitions		2,186	2,095
Decrease from disposition of business		(1,300)	(4,994)
Goodwill impairment charge	$ (34,000)	0	(34,013)	$ (31,992)
Foreign currency translation		3,796	3,170
Goodwill, end of period		478,523	465,154	453,105
Technical Services
Goodwill [Roll Forward]
Goodwill, beginning of period		61,116	49,267
Increase from current period acquisitions		0	12,572
Measurement period adjustments from prior period acquisitions		0	0
Decrease from disposition of business		(1,300)	0
Goodwill impairment charge			0
Foreign currency translation		317	(723)
Goodwill, end of period		60,133	61,116	49,267
Industrial and Field Services
Goodwill [Roll Forward]
Goodwill, beginning of period		107,968	105,286
Increase from current period acquisitions		3,000	6,953
Measurement period adjustments from prior period acquisitions		0	0
Decrease from disposition of business		0	(4,994)
Goodwill impairment charge			0
Foreign currency translation		1,285	723
Goodwill, end of period		112,253	107,968	105,286
Safety-Kleen
Goodwill [Roll Forward]
Goodwill, beginning of period		296,070	266,344
Increase from current period acquisitions		5,687	26,266
Measurement period adjustments from prior period acquisitions		2,186	2,095
Decrease from disposition of business		0	0
Goodwill impairment charge			0
Foreign currency translation		2,194	1,365
Goodwill, end of period		306,137	296,070	266,344
Oil, Gas and Lodging Services
Goodwill [Roll Forward]
Goodwill, beginning of period		0	32,208
Increase from current period acquisitions		0	0
Measurement period adjustments from prior period acquisitions		0	0
Decrease from disposition of business		0	0
Goodwill impairment charge			(34,013)
Foreign currency translation		0	1,805
Goodwill, end of period		$ 0	$ 0	$ 32,208

GOODWILL AND OTHER INTANGIBLE78

GOODWILL AND OTHER INTANGIBLE ASSETS (Narrative) (Details) - USD ($)	3 Months Ended		12 Months Ended
	Sep. 30, 2016	Jun. 30, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Indefinite-lived Intangible Assets [Line Items]
Accumulated goodwill impairment charges			$ 189,400,000
Goodwill impairment charge	$ 34,000,000		0	$ 34,013,000	$ 31,992,000
Property, plant and equipment, net			1,587,365,000	1,611,827,000
Intangible assets			469,128,000	498,721,000
Amortization expense of permits and other intangible assets			37,000,000	40,000,000	40,200,000
Lodging Segment
Indefinite-lived Intangible Assets [Line Items]
Goodwill impairment charge				34,000,000
Oil and Gas Field Services
Indefinite-lived Intangible Assets [Line Items]
Goodwill impairment charge					$ 32,000,000
Oil, Gas and Lodging Services
Indefinite-lived Intangible Assets [Line Items]
Goodwill impairment charge				34,013,000
Property, plant and equipment, net			168,294,000	182,038,000
Intangible assets			6,695,000	10,889,000
Oil, Gas and Lodging Services | Lodging Segment
Indefinite-lived Intangible Assets [Line Items]
Goodwill impairment charge	34,000,000
Goodwill	34,000,000
Fair value of goodwill	$ 0
Property, plant and equipment, net			95,600,000
Intangible assets			3,900,000
Oil, Gas and Lodging Services | Oil and Gas Field Services
Indefinite-lived Intangible Assets [Line Items]
Goodwill impairment charge		$ 32,000,000
Fair value of goodwill		$ 0
Property, plant and equipment, net			72,700,000
Intangible assets			2,800,000
Safety-Kleen
Indefinite-lived Intangible Assets [Line Items]
Goodwill impairment charge				0
Property, plant and equipment, net			582,162,000	584,647,000
Intangible assets			$ 371,609,000	$ 391,390,000

GOODWILL AND OTHER INTANGIBLE79

GOODWILL AND OTHER INTANGIBLE ASSETS (Finite-lived and Indefinite Lived Intangible Assets) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Finite-lived intangible assets
Accumulated Amortization	$ 264,911	$ 223,219
Net	345,800
Total permits and other intangible assets, cost	734,039	721,940
Total permits and other intangible assets, net	469,128	498,721
Trademarks and trade names
Finite-lived intangible assets
Trademarks and trade names	123,328	122,623
Permits
Finite-lived intangible assets
Cost	174,721	171,637
Accumulated Amortization	74,347	67,301
Net	100,374	104,336
Customer and supplier relationships
Finite-lived intangible assets
Cost	399,224	393,426
Accumulated Amortization	158,972	127,462
Net	240,252	265,964
Other intangible assets
Finite-lived intangible assets
Cost	36,766	34,254
Accumulated Amortization	31,592	28,456
Net	5,174	5,798
Total amortizable permits and other intangible assets
Finite-lived intangible assets
Cost	610,711	599,317
Accumulated Amortization	264,911	223,219
Net	$ 345,800	$ 376,098

GOODWILL AND OTHER INTANGIBLE80

GOODWILL AND OTHER INTANGIBLE ASSETS (Expected Amortization) (Details) $ in Thousands	Dec. 31, 2017USD ($)
Expected amortization
2,018	$ 34,631
2,019	31,684
2,020	29,130
2,021	26,888
2,022	26,727
Thereafter	196,740
Net	$ 345,800

ACCRUED EXPENSES (Details)

ACCRUED EXPENSES (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Payables and Accruals [Abstract]
Insurance	$ 57,889	$ 63,061
Interest	12,660	21,536
Accrued compensation and benefits	55,861	34,641
Income, real estate, sales and other taxes	27,330	35,083
Other	34,242	36,400
Total accrued expenses	187,982	190,721
Accrued legal matters	1,400	3,800
Accrued severance charges	$ 3,500	$ 2,900

CLOSURE AND POST-CLOSURE LIAB82

CLOSURE AND POST-CLOSURE LIABILITIES (Changes in Post-Closure Liabilities) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Changes to post-closure liabilities
Balance at the beginning of the period	$ 58,331	$ 56,249
Liabilities assumed in acquisitions	59	2,408
Measurement period adjustments from prior period acquisitions	596	657
New asset retirement obligations	1,881	1,983
Measurement period adjustments from prior period acquisitions	(1,170)
Accretion	4,748	5,103
Changes in estimates recorded to statement of operations	(240)	(2,619)
Changes in estimates recorded to balance sheet	(227)	(3,289)
Expenditures	(3,225)	(2,248)
Currency translation and other	284	87
Balance at the end of the period	$ 61,037	$ 58,331
Asset retirement obligations discount rate	6.32%	6.23%
Landfill Retirement Liability
Changes to post-closure liabilities
Balance at the beginning of the period	$ 30,630	$ 32,023
Liabilities assumed in acquisitions	0	0
Measurement period adjustments from prior period acquisitions	0	0
New asset retirement obligations	1,881	1,983
Measurement period adjustments from prior period acquisitions	0
Accretion	2,243	2,705
Changes in estimates recorded to statement of operations	(131)	(1,415)
Changes in estimates recorded to balance sheet	364	(3,289)
Expenditures	(2,777)	(1,446)
Currency translation and other	172	69
Balance at the end of the period	32,382	30,630
Non-Landfill Retirement Liability
Changes to post-closure liabilities
Balance at the beginning of the period	27,701	24,226
Liabilities assumed in acquisitions	59	2,408
Measurement period adjustments from prior period acquisitions	596	657
Measurement period adjustments from prior period acquisitions	(1,170)
Accretion	2,505	2,398
Changes in estimates recorded to statement of operations	(109)	(1,204)
Changes in estimates recorded to balance sheet	(591)	0
Expenditures	(448)	(802)
Currency translation and other	112	18
Balance at the end of the period	$ 28,655	$ 27,701

CLOSURE AND POST-CLOSURE LIAB83

CLOSURE AND POST-CLOSURE LIABILITIES (Anticipated Payments) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Environmental Property Sale, Disposal or Abandonment Costs
2,018	$ 6,313
2,019	8,957
2,020	12,152
2,021	8,652
2,022	353
Thereafter	285,404
Undiscounted closure and post-closure liabilities	321,831
Less: Discount at credit-adjusted risk-free rate	(161,767)
Less: Undiscounted estimated closure and post-closure liabilities relating to airspace not yet consumed	(99,027)
Present value of closure and post-closure liabilities	$ 61,037	$ 58,331	$ 56,249

REMEDIAL LIABILITIES (Changes i

REMEDIAL LIABILITIES (Changes in Remedial Liabilities) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Changes to remedial liabilities
Balance at the beginning of the period	$ 128,007	$ 131,992
Liabilities assumed in acquisitions		2,041
Measurement period adjustments from prior period acquisitions	504
Accretion	4,712	5,074
Changes in estimates recorded to statement of operations	45	(1,635)
Expenditures	(9,740)	(9,922)
Currency translation and other	940	457
Balance at the end of the period	124,468	128,007
Remedial Liabilities for Landfill Sites
Changes to remedial liabilities
Balance at the beginning of the period	1,777	2,327
Liabilities assumed in acquisitions		0
Measurement period adjustments from prior period acquisitions	0
Accretion	86	110
Changes in estimates recorded to statement of operations	(21)	(538)
Expenditures	(42)	(122)
Currency translation and other	0	0
Balance at the end of the period	1,800	1,777
Remedial Liabilities for Inactive Sites
Changes to remedial liabilities
Balance at the beginning of the period	64,151	63,613
Liabilities assumed in acquisitions		0
Measurement period adjustments from prior period acquisitions	0
Accretion	2,648	2,737
Changes in estimates recorded to statement of operations	(289)	1,520
Expenditures	(3,906)	(3,893)
Currency translation and other	2,738	174
Balance at the end of the period	65,342	64,151
Remedial Liabilities (Including Superfund) for Non-Landfill Operations
Changes to remedial liabilities
Balance at the beginning of the period	62,079	66,052
Liabilities assumed in acquisitions		2,041
Measurement period adjustments from prior period acquisitions	504
Accretion	1,978	2,227
Changes in estimates recorded to statement of operations	355	(2,617)
Expenditures	(5,792)	(5,907)
Currency translation and other	(1,798)	283
Balance at the end of the period	$ 57,326	$ 62,079

REMEDIAL LIABILITIES (Additiona

REMEDIAL LIABILITIES (Additional Information) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Environmental Remediation Obligations [Abstract]
Changes in estimates recorded to statement of income (loss)	$ 45	$ (1,635)
Future remediation liability	124,468	$ 128,007	$ 131,992
Possible increase in total remedial liabilities	$ 23,100
Accrual for environmental loss contingencies, threshold for disclosure (as a percent)	5.00%

REMEDIAL LIABILITIES (Anticipat

REMEDIAL LIABILITIES (Anticipated Payments) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accrual for Environmental Loss Contingencies, Net [Abstract]
2,018	$ 14,507
2,019	16,934
2,020	15,259
2,021	10,212
2,022	7,566
Thereafter	83,767
Undiscounted remedial liabilities	148,245
Less: Discount	(23,777)
Total remedial liabilities	$ 124,468	$ 128,007	$ 131,992

REMEDIAL LIABILITIES (Estimates

REMEDIAL LIABILITIES (Estimates) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)sitefacility	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Site Contingency [Line Items]
Remedial Liability	$ 124,468	$ 128,007	$ 131,992
% of Total	100.00%
Reasonably possible additional liabilities	$ 23,053
Legal and Administrative Proceedings
Site Contingency [Line Items]
Remedial Liability	17,900
Reasonably possible additional liabilities	1,800
Facilities now used in active conduct of the Company's business (44 facilities)
Site Contingency [Line Items]
Remedial Liability	$ 54,193
% of Total	43.50%
Reasonably possible additional liabilities	$ 11,747
Number of facility by type | facility	44
Inactive facilities not now used in active conduct of the Company's business but most of which were acquired because the assumption of remedial liabilities for such facilities was part of the purchase price for the CSD assets (38 facilities)
Site Contingency [Line Items]
Remedial Liability	$ 62,706
% of Total	50.40%
Reasonably possible additional liabilities	$ 10,549
Number of facility by type | facility	38
Superfund sites owned by third parties (16 sites)
Site Contingency [Line Items]
Remedial Liability	$ 7,569
% of Total	6.10%
Reasonably possible additional liabilities	$ 757
Number of facility by type | site	16
Superfund sites owned by third parties (16 sites) | Various
Site Contingency [Line Items]
Remedial Liability	$ 7,569
% of Total	6.10%
Reasonably possible additional liabilities	$ 757
Number of facility by type | site	16
Closed incinerator and landfill | Baton Rouge LA
Site Contingency [Line Items]
Remedial Liability	$ 23,357
% of Total	18.80%
Reasonably possible additional liabilities	$ 3,938
Closed incinerator | Bridgeport, NJ
Site Contingency [Line Items]
Remedial Liability	$ 18,394
% of Total	14.80%
Reasonably possible additional liabilities	$ 2,534
Idled incinerator and legal proceedings | Mercier Quebec
Site Contingency [Line Items]
Remedial Liability	$ 10,414
% of Total	8.40%
Reasonably possible additional liabilities	$ 1,105
Operating solvent recycling center | Linden, NJ
Site Contingency [Line Items]
Remedial Liability	$ 7,678
% of Total	6.20%
Reasonably possible additional liabilities	$ 825
All other incinerators, landfills, wastewater treatment facilities and service centers (78 facilities) | Various
Site Contingency [Line Items]
Remedial Liability	$ 57,056
% of Total	45.70%
Reasonably possible additional liabilities	$ 13,894
Number of facility by type | facility	78

FINANCING ARRANGEMENTS (Summary

FINANCING ARRANGEMENTS (Summary of Financing Arrangements) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 07, 2012	Jul. 30, 2012
Debt Instrument [Line Items]
Current portion of long-term obligations	$ 4,000	$ 0
Long-term obligations, at par	1,639,000	1,645,000
Unamortized debt issuance costs and premium, net	(13,463)	(11,728)
Long-term obligations, at carrying value	1,625,537	1,633,272
Secured Debt | Term Loan Agreement
Debt Instrument [Line Items]
Current portion of long-term obligations	4,000	0
Long-term obligations, at par	394,000	0
Senior Notes | Senior unsecured notes, at 5.25%, due August 1, 2020 (2020 Notes)
Debt Instrument [Line Items]
Long-term obligations, at par	$ 400,000	800,000
Interest rate	5.25%			5.25%
Senior Notes | Senior unsecured notes, at 5.125%, due June 1, 2021 (2021 Notes)
Debt Instrument [Line Items]
Long-term obligations, at par	$ 845,000	$ 845,000
Interest rate	5.125%		5.125%

FINANCING ARRANGEMENTS (Narrati

FINANCING ARRANGEMENTS (Narrative) (Details) - USD ($)	Aug. 01, 2017	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Mar. 14, 2016	Dec. 07, 2012	Jul. 30, 2012
Financing arrangements
Debt Instrument, Periodic Payment, Percentage of Face Amount			0.25%
Revolving credit facility, available borrowing capacity			$ 217,800,000	$ 195,200,000
Letters of credit outstanding, amount			134,100,000	132,600,000
Premiums to repay debt early			$ 6,028,000	0	$ 0
Parent and Domestic Subsidiaries
Financing arrangements
Credit available subject to percentage of accounts receivable			85.00%
Credit available subject to percentage of cash deposited			100.00%
Canadian Subsidiaries
Financing arrangements
Credit available subject to percentage of accounts receivable			85.00%
Credit available subject to percentage of cash deposited			100.00%
Term Loan Agreement | Eurodollar
Financing arrangements
Basis spread on variable rate		2.00%
Term Loan Agreement | Base rate loans
Financing arrangements
Basis spread on variable rate		1.00%
Term Loan Agreement | Minimum | Base rate loans
Financing arrangements
Basis spread on variable rate		0.00%
Secured Debt | Term Loan Agreement
Financing arrangements
Face amount		$ 400,000,000
Fair value of notes			$ 400,500,000
Effective interest rate						3.57%
Premiums to repay debt early	$ 6,000,000
Expenses incurred from financing	6,500,000
Secured Debt | Repurchased Notes
Financing arrangements
Repurchased amount		296,200,000
Amount used to repurchase notes		312,600,000
Accrued interest paid		6,400,000
Unsecured Debt | Senior unsecured notes, at 5.25%, due August 1, 2020 (2020 Notes)
Financing arrangements
Face amount		$ 503,800,000
Repurchased amount	$ 103,800,000
Redemption price percentage	101.313%
Senior Notes | Senior unsecured notes, at 5.25%, due August 1, 2020 (2020 Notes)
Financing arrangements
Face amount									$ 800,000,000
Interest rate			5.25%						5.25%
Fair value of notes			$ 404,600,000	820,000,000
Repurchased amount			$ 400,000,000
Senior Notes | Senior unsecured notes, at 5.125%, due June 1, 2021 (2021 Notes)
Financing arrangements
Face amount							$ 250,000,000	$ 600,000,000
Interest rate			5.125%					5.125%
Fair value of notes			$ 855,700,000	$ 861,900,000
Repurchased amount					$ 5,000,000
Revolving credit facility
Financing arrangements
Revolving credit facility, maximum borrowing capacity			$ 400,000,000
Period for measurement of average liquidity			30 days
Revolving credit facility | Minimum
Financing arrangements
Commitment fee			0.25%
Revolving credit facility | Minimum | LIBOR loans
Financing arrangements
Basis spread on variable rate			1.25%
Revolving credit facility | Minimum | Base rate loans
Financing arrangements
Basis spread on variable rate			0.25%
Revolving credit facility | Maximum
Financing arrangements
Commitment fee			0.30%
Revolving credit facility | Maximum | LIBOR loans
Financing arrangements
Basis spread on variable rate			1.50%
Revolving credit facility | Maximum | Base rate loans
Financing arrangements
Basis spread on variable rate			0.50%
Revolving credit facility | Parent and Domestic Subsidiaries
Financing arrangements
Revolving credit facility, maximum borrowing capacity			$ 300,000,000
Revolving credit facility | Canadian Subsidiaries
Financing arrangements
Revolving credit facility, maximum borrowing capacity			100,000,000
Letters of credit | Parent and Domestic Subsidiaries
Financing arrangements
Revolving credit facility, maximum borrowing capacity			250,000,000
Letters of credit | Canadian Subsidiaries
Financing arrangements
Revolving credit facility, maximum borrowing capacity			$ 75,000,000

FINANCING ARRANGEMENTS (Schedul

FINANCING ARRANGEMENTS (Schedule of Redemption Prices) (Details) - Senior Notes	12 Months Ended
	Dec. 31, 2017
Senior unsecured notes, at 5.25%, due August 1, 2020 (2020 Notes)
Debt Instrument [Line Items]
Prior to period one	101.313%
After to period one	100.00%
Senior unsecured notes, at 5.125%, due June 1, 2021 (2021 Notes)
Debt Instrument [Line Items]
Prior to period one	101.281%
After to period one	100.00%

INCOME TAXES (Provision for Tax

INCOME TAXES (Provision for Tax Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Noncontrolling Interest [Abstract]
Domestic	$ 101,714	$ 87,328	$ 164,105
Foreign	(43,025)	(78,612)	(54,459)
Income (loss) before (benefit) provision for income taxes	58,689	8,716	109,646
Current:
Federal	25,613	14,798	46,775
State	11,083	8,763	11,120
Foreign	4,589	9,844	5,719
Current Income Tax Expense (Benefit)	41,285	33,405	63,614
Deferred
Federal	(85,488)	21,814	12,254
State	1,085	1,644	2,766
Foreign	1,068	(8,274)	(13,090)
Deferred income taxes	(83,335)	15,184	1,930
(Benefit) provision for income taxes	(42,050)	48,589	65,544
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Tax expense at US statutory rate	20,541	3,051	38,376
State income taxes, net of federal benefit	4,547	6,010	8,449
Foreign rate differential	3,733	3,646	3,951
Valuation allowance	16,552	22,564	1,824
Uncertain tax position interest and penalties	3,730	107	32
Goodwill impairment	0	11,905	10,974
Other	1,856	1,306	1,938
Adjustment for Tax Cuts and Jobs Act	(93,009)	0	0
(Benefit) provision for income taxes	$ (42,050)	$ 48,589	$ 65,544

INCOME TAXES (Deferred Tax Asse

INCOME TAXES (Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Provision for doubtful accounts	$ 7,417	$ 11,189
Closure, post-closure and remedial liabilities	28,189	40,829
Accrued expenses	15,382	19,826
Accrued compensation	1,903	2,747
Net operating loss carryforwards	46,650	46,752
Tax credit carryforwards	17,504	25,348
Uncertain tax positions accrued interest and federal benefit	921	1,241
Stock-based compensation	2,268	1,993
Other	3,258	555
Total deferred tax assets	123,492	150,480
Deferred tax liabilities:
Property, plant and equipment	(144,325)	(207,799)
Permits and other intangible assets	(107,407)	(161,295)
Prepaids	(8,080)	(11,030)
Total deferred tax liabilities	(259,812)	(380,124)
Total net deferred tax liability before valuation allowance	(136,320)	(229,644)
Less valuation allowance	(68,355)	(55,189)
Total net deferred tax liability before valuation allowance	(204,675)	$ (284,833)
State and local operating loss carryforwards	186,700
Federal operating loss carryforwards	48,000
Foreign operating loss carryforwards	116,100
Foreign tax credit carryforwards	$ 17,500

INCOME TAXES (Additional Inform

INCOME TAXES (Additional Information) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Effective income tax rate		(71.60%)	557.50%	59.80%
Net benefit from enacted tax act	$ 93,000
Tax benefit due to reduction in net deferred tax liability	100,500
One-time tax expense on deemed repatriation	7,500
Tax effects		$ (269)	$ 16,918	$ 7
Valuation allowance	68,355	68,355	55,189
Valuation allowance, foreign tax credits	17,500	17,500	25,000
Valuation allowance, federal net operating loss carryforwards	3,900	3,900	1,500
Valuation allowance, state net operating loss carryforwards	11,900	11,900	5,000
Valuation allowance, foreign net operating loss carryforwards	22,600	22,600	18,000
Valuation allowance, deferred tax assets of Canadian subsidiary	12,500	12,500	5,700
Unrecognized tax benefits that would impact effective tax rate	5,100	5,100	1,700	2,100
Unrecognized tax benefits, income tax penalties and interest accrued	$ 900	900	300	400
Unrecognized tax benefits, penalties and interest		500	100	100
Reduction in unrecognized tax benefit from the expiration of statue of limitations and the resolution of tax audits		1,400
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Tax effects		$ 0	$ 16,761	$ 0

INCOME TAXES (Unrecognized Tax

INCOME TAXES (Unrecognized Tax Benefits) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits at beginning of year	$ 1,738	$ 2,064	$ 2,537
Additions to current year tax positions	1,457	0	0
Additions to prior year tax positions	2,031	0	0
Settlements	(231)	(533)	(217)
Foreign currency translation	126	207	(256)
Unrecognized tax benefits at end of year	$ 5,121	$ 1,738	$ 2,064

EARNINGS (LOSS) PER SHARE (Reco

EARNINGS (LOSS) PER SHARE (Reconciliation of Basic and Diluted Earnings Per Share Computations) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator for basic and diluted (loss) earnings per share:
Net (loss) income	$ 84,194	$ 12,058	$ 25,880	$ (21,393)	$ (12,713)	$ (10,255)	$ 3,966	$ (20,871)	$ 100,739	$ (39,873)	$ 44,102
Denominator:
Weighted basic shares outstanding (in shares)									57,072	57,532	58,324
Dilutive effect of equity-based compensation awards (in shares)									128	0	110
Weighted dilutive shares outstanding (in shares)									57,200	57,532	58,434
Basic earnings (loss) per share (in dollars per share)									$ 1.77	$ (0.69)	$ 0.76
Diluted earnings (loss) per share (in dollars per share)									$ 1.76	$ (0.69)	$ 0.76

EARNINGS (LOSS) PER SHARE (Anti

EARNINGS (LOSS) PER SHARE (Anti-Dilutive Securities) (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2015
Restricted Stock and Performance Stock Awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	730,929
Performance Stock Awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	152,831	154,577
Restricted Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	49,373	31,656

STOCKHOLDERS' EQUITY (Details)

STOCKHOLDERS' EQUITY (Details) - USD ($) shares in Thousands	12 Months Ended			34 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Oct. 31, 2017	Oct. 30, 2017
Class of Stock [Line Items]
Repurchases of common stock	$ 48,971,000	$ 22,188,000	$ 73,347,000
Common Stock
Class of Stock [Line Items]
Stock repurchase program, authorized amount					$ 600,000,000	$ 300,000,000
Repurchase of common stock (in shares)	907	453	1,422	4,800
Repurchases of common stock	$ 9,000	$ 4,000	$ 14,000	$ 248,800,000
Stock repurchase program, remaining authorized repurchase amount	351,200,000			$ 351,200,000
Additional Paid-in Capital
Class of Stock [Line Items]
Repurchases of common stock	$ 48,962,000	$ 22,184,000	$ 73,333,000

ACCUMULATED OTHER COMPREHENSI98

ACCUMULATED OTHER COMPREHENSIVE LOSS (Components of AOCI) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Increase (Decrease) in Equity
Other comprehensive loss before reclassifications	$ 41,966	$ 23,648	$ (144,057)
Amounts reclassified out of accumulated other comprehensive loss	222	0	0
Tax effects	(269)	16,918	7
Other comprehensive loss	41,919	40,566	(144,050)
Foreign Currency Translation Adjustments
Increase (Decrease) in Equity
Beginning balance	(212,211)	(252,939)	(108,889)
Other comprehensive loss before reclassifications	41,636	23,967	(144,050)
Amounts reclassified out of accumulated other comprehensive loss	0	0	0
Tax effects	0	16,761	0
Other comprehensive loss	41,636	40,728	(144,050)
Ending balance	(170,575)	(212,211)	(252,939)
Unrealized (Losses) Gains on Available-for-Sale Securities
Increase (Decrease) in Equity
Beginning balance	(321)	0	0
Other comprehensive loss before reclassifications	184	(535)	0
Amounts reclassified out of accumulated other comprehensive loss	222	0	0
Tax effects	(231)	214	0
Other comprehensive loss	175	(321)	0
Ending balance	(146)	(321)	0
Unfunded Pension Liability
Increase (Decrease) in Equity
Beginning balance	(1,794)	(1,953)	(1,953)
Other comprehensive loss before reclassifications	146	216	(7)
Amounts reclassified out of accumulated other comprehensive loss	0	0	0
Tax effects	(38)	(57)	7
Other comprehensive loss	108	159	0
Ending balance	(1,686)	(1,794)	(1,953)
Accumulated Other Comprehensive loss
Increase (Decrease) in Equity
Beginning balance	(214,326)	(254,892)	(110,842)
Ending balance	$ (172,407)	$ (214,326)	$ (254,892)

ACCUMULATED OTHER COMPREHENSI99

ACCUMULATED OTHER COMPREHENSIVE LOSS (Reclassification out of AOCI) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified out of accumulated other comprehensive loss	$ (222)	$ 0	$ 0
Unrealized (losses) gains on available-for-sale securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified out of accumulated other comprehensive loss	$ (222)	$ 0	$ 0

STOCK-BASED COMPENSATION AND100

STOCK-BASED COMPENSATION AND EMPLOYEE BENEFIT PLANS (Stock-Based Compensation) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 13.1	$ 10.5	$ 8.6
Total income tax benefit from stock-based compensation	$ 3.7
Restricted Stock | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period (in years)	3 years
Restricted Stock | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period (in years)	5 years
2000 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding, number (in shares)	0
2010 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized (in shares)				6,000,000
Vested in 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total income tax benefit from stock-based compensation	$ 0.4
Vested in 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total income tax benefit from stock-based compensation		$ 2.8
Vested in 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total income tax benefit from stock-based compensation			$ 2.3

STOCK-BASED COMPENSATION AND101

STOCK-BASED COMPENSATION AND EMPLOYEE BENEFIT PLANS (Restricted Stock Awards) (Details) - Restricted Stock - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Number of Shares
Unvested, beginning of period (in shares)	510,041
Granted (in shares)	307,455
Vested (in shares)	(136,787)
Forfeited (in shares)	(75,776)
Unvested, end of period (in shares)	604,933	510,041
Weighted Average Grant-Date Fair Value
Unvested, beginning of period (in dollars per share)	$ 52.65
Granted (in dollars per share)	55.93
Vested (in dollars per share)	53.16
Forfeited (in dollars per share)	52.46
Unvested, end of period (in dollars per share)	$ 54.23	$ 52.65
Total unrecognized compensation cost	$ 24.1
Expected to be recognized over a weighted average period	2 years 280 days
Total fair value, vested in period	$ 7.3	$ 8.3	$ 6.9
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period (in years)	3 years
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period (in years)	5 years

STOCK-BASED COMPENSATION AND102

STOCK-BASED COMPENSATION AND EMPLOYEE BENEFIT PLANS (Performance Stock Awards) (Details) - Performance Stock Awards - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance evaluation stock-based compensation	2 years
Number of Shares
Unvested, beginning of period (in shares)	220,882
Granted (in shares)	170,897
Vested (in shares)	(53,096)
Forfeited (in shares)	(148,554)
Unvested, end of period (in shares)	190,129	220,882
Weighted Average Grant-Date Fair Value
Unvested, beginning of period (in dollars per share)	$ 54.69
Granted (in dollars per share)	55.87
Forfeited (in dollars per share)	57.14
Vested (in dollars per share)	55.60
Unvested, end of period (in dollars per share)	$ 55.63	$ 54.69
Total unrecognized compensation cost	$ 2.5
Total fair value, vested in period	$ 3	$ 1	$ 0.6

STOCK-BASED COMPENSATION AND103

STOCK-BASED COMPENSATION AND EMPLOYEE BENEFIT PLANS (Employee Benefit Plans) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)employee	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Defined Contribution Plan Disclosure [Line Items]
Number of active non-supervisory Canadian employees | employee	12
Net periodic benefit cost	$ 0.4	$ 0.4	$ 0.3
Pension assets measured at fair value	9.3	8.4
Projected benefit obligation	10.9	9.9
Level 1
Defined Contribution Plan Disclosure [Line Items]
Pension assets measured at fair value	3.9	3.5
Level 2
Defined Contribution Plan Disclosure [Line Items]
Pension assets measured at fair value	$ 5.4	$ 4.9

COMMITMENTS AND CONTINGENCIE104

COMMITMENTS AND CONTINGENCIES (Legal and Administrative Proceedings) (Details) CAD in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)claimproceeding	Dec. 31, 2012CAD	Dec. 31, 1999municipality	Dec. 31, 1968permit	Dec. 31, 2016USD ($)
Legal and Administrative Proceedings
Reserves	$ 19.3				$ 22
Safety-Kleen
Legal and Administrative Proceedings
Number of proceedings | proceeding	52
Loss contingency, claims settled and dismissed, claims | claim	33
Legal and Administrative Proceedings
Legal and Administrative Proceedings
Reserves	$ 17.9				18.2
Possible increase in legal and administrative proceedings	1.8				1.9
Ville Mercier
Legal and Administrative Proceedings
Number of permits issued by government, for dumping organic liquid | permit				2
Number of neighboring municipalities filing separate legal proceedings against the Mercier subsidiary and the government of Quebec | municipality			3
General damages sought | CAD		CAD 2.9
Punitive damages sought | CAD		CAD 10
Federal, State, and Provincial Enforcement Actions
Legal and Administrative Proceedings
Reserves relating to legal and administrative proceedings	$ 1.4				$ 3.8
Number of proceedings | proceeding	5

COMMITMENTS AND CONTINGENCIE105

COMMITMENTS AND CONTINGENCIES (Superfund Proceedings) (Details)	12 Months Ended
	Dec. 31, 2017USD ($)site
Superfund Proceedings
Number of sites owned by the entity subject to proceedings under federal or state superfund laws	129
Superfund Proceedings
Superfund Proceedings
Number of sites subject to proceedings under federal or state superfund laws	129
Number of sites owned by the entity subject to proceedings under federal or state superfund laws	3
Number of sites owned by third parties subject to proceedings under federal or state superfund laws	126
Number of sites for which environmental remediation expense is settled	33
Third party sites requiring expenditure on remediation	16
Number of sites for which environmental remediation expense is not required	77
Possible increase in legal and administrative proceedings | $	$ 100,000
Number of sites which potential liability could exceed $100,000	11
Notices received from owners of third party sites seeking indemnification from the company	6
Certain other third party sites
Superfund Proceedings
Indemnification agreement with third party sites, sites	11
Safety-Kleen
Superfund Proceedings
Notices received from owners of third party sites seeking indemnification from the company	17

COMMITMENTS AND CONTINGENCIE106

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

COMMITMENTS AND CONTINGENCIE107

COMMITMENTS AND CONTINGENCIES (Leases) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Lease terms range minimum	1 year
Lease terms range maximum	24 years
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,018	$ 44,476
2,019	37,161
2,020	30,233
2,021	22,173
2,022	17,432
Thereafter	45,370
Total minimum lease payments	196,845
Operating leases, rent expense, net	$ 125,400	$ 121,900	$ 135,500

COMMITMENTS AND CONTINGENCIE108

COMMITMENTS AND CONTINGENCIES (Other Contingencies) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Product Liability Contingency [Line Items]
Retention for environmental impairment	$ 1,000
Self-insurance liabilities	$ 47,900	$ 46,500
Weighted average risk free discount rate for self insurance liabilities	1.87%	1.16%
Self Insurance Losses Expected [Abstract]
2,018	$ 16,525
2,019	11,259
2,020	7,848
2,021	4,393
2,022	3,688
Thereafter	5,769
Undiscounted self-insurance liabilities	49,482
Less: Discount	1,568
Total self-insurance liabilities (included in accrued expenses)	47,914
Minimum
Product Liability Contingency [Line Items]
Deductible health insurance policy	700
Safety-Kleen
Product Liability Contingency [Line Items]
Deductible per occurrence for workers compensation	1,000
Deductible per occurrence for general liability	2,000
Deductible per occurrence for vehicle liability	$ 2,000

SEGMENT REPORTING (Segment Info

SEGMENT REPORTING (Segment Information, Revenues, EBITA, and Reconciliation to the Consolidated Statement of Operations) (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Dec. 31, 2017USD ($)operationsegment	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Segment Reporting Information [Line Items]
Reporting segments number | segment									6
Number of operations for which the revenues are insignificant | operation									2
Total revenues	$ 747,403	$ 755,846	$ 752,788	$ 688,941	$ 692,113	$ 729,520	$ 697,510	$ 636,083	$ 2,944,978	$ 2,755,226	$ 3,275,137
Adjusted EBITDA									425,657	400,354	504,167
Reconciliation to Consolidated Statements of Operations:
Accretion of environmental liabilities									9,460	10,177	10,402
Depreciation and amortization									288,422	287,002	274,194
Goodwill impairment charges						34,000			0	34,013	31,992
Income (loss) from operations	27,935	47,663	46,744	5,433	21,943	16,802	34,504	(4,087)	127,775	69,162	187,579
Other expense (income), net	$ 3,305	432	833	$ 1,549	$ (6,932)	198	$ 189	$ 350	6,119	(6,195)	1,380
Loss on early extinguishment of debt		$ 1,900	6,000						7,891	0	0
Gain on sale of businesses			$ (31,700)			$ (16,400)			(30,732)	(16,884)	0
Interest expense, net of interest income									85,808	83,525	76,553
Income (loss) before (benefit) provision for income taxes									58,689	8,716	109,646
Technical Services
Segment Reporting Information [Line Items]
Total revenues									1,144,149	1,056,735	1,139,080
Adjusted EBITDA									276,592	271,176	291,737
Reconciliation to Consolidated Statements of Operations:
Goodwill impairment charges										0
Industrial and Field Services
Segment Reporting Information [Line Items]
Total revenues									593,722	582,215	989,953
Adjusted EBITDA									43,010	51,191	161,447
Reconciliation to Consolidated Statements of Operations:
Goodwill impairment charges										0
Safety-Kleen
Segment Reporting Information [Line Items]
Total revenues									1,087,886	996,083	941,689
Adjusted EBITDA									249,811	219,546	172,262
Reconciliation to Consolidated Statements of Operations:
Goodwill impairment charges										0
Oil, Gas and Lodging Services
Segment Reporting Information [Line Items]
Total revenues									119,603	119,883	207,139
Adjusted EBITDA									1,708	(3,292)	11,704
Reconciliation to Consolidated Statements of Operations:
Goodwill impairment charges										34,013
Corporate Items
Segment Reporting Information [Line Items]
Total revenues									(382)	310	(2,724)
Adjusted EBITDA									(145,464)	(138,267)	(132,983)
Direct revenues
Segment Reporting Information [Line Items]
Total revenues									2,944,978	2,755,226	3,275,137
Direct revenues | Technical Services
Segment Reporting Information [Line Items]
Total revenues									980,232	906,495	991,410
Direct revenues | Industrial and Field Services
Segment Reporting Information [Line Items]
Total revenues									631,216	618,245	1,023,638
Direct revenues | Safety-Kleen
Segment Reporting Information [Line Items]
Total revenues									1,213,703	1,110,727	1,060,926
Direct revenues | Oil, Gas and Lodging Services
Segment Reporting Information [Line Items]
Total revenues									117,252	116,692	198,705
Direct revenues | Corporate Items
Segment Reporting Information [Line Items]
Total revenues									2,575	3,067	458
Intersegment revenues, net | Technical Services
Segment Reporting Information [Line Items]
Total revenues									161,533	147,866	144,084
Intersegment revenues, net | Industrial and Field Services
Segment Reporting Information [Line Items]
Total revenues									(37,694)	(35,724)	(32,903)
Intersegment revenues, net | Safety-Kleen
Segment Reporting Information [Line Items]
Total revenues									(125,822)	(115,013)	(119,232)
Intersegment revenues, net | Oil, Gas and Lodging Services
Segment Reporting Information [Line Items]
Total revenues									1,983	2,871	8,051
Intersegment revenues, net | Corporate Items
Segment Reporting Information [Line Items]
Total revenues									0	0	0
Corporate Items, net
Segment Reporting Information [Line Items]
Total revenues									0	0	0
Corporate Items, net | Technical Services
Segment Reporting Information [Line Items]
Total revenues									2,384	2,374	3,586
Corporate Items, net | Industrial and Field Services
Segment Reporting Information [Line Items]
Total revenues									200	(306)	(782)
Corporate Items, net | Safety-Kleen
Segment Reporting Information [Line Items]
Total revenues									5	369	(5)
Corporate Items, net | Oil, Gas and Lodging Services
Segment Reporting Information [Line Items]
Total revenues									368	320	383
Corporate Items, net | Corporate Items
Segment Reporting Information [Line Items]
Total revenues									$ (2,957)	$ (2,757)	$ (3,182)

SEGMENT REPORTING (Segment Addi

SEGMENT REPORTING (Segment Additional Information) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Total revenues	$ 747,403	$ 755,846	$ 752,788	$ 688,941	$ 692,113	$ 729,520	$ 697,510	$ 636,083	$ 2,944,978	$ 2,755,226	$ 3,275,137
Property, plant and equipment, net	1,587,365				1,611,827				1,587,365	1,611,827
Permits and other intangibles, net	469,128				498,721				469,128	498,721
Goodwill	478,523				465,154				478,523	465,154	453,105
Goodwill and Permits and other intangibles, net	947,651				963,875				947,651	963,875
Assets	3,706,570				3,681,920				3,706,570	3,681,920	3,431,428
Technical Services
Total revenues									1,144,149	1,056,735	1,139,080
Property, plant and equipment, net	504,754				521,134				504,754	521,134
Permits and other intangibles, net	73,775				78,625				73,775	78,625
Goodwill	60,133				61,116				60,133	61,116	49,267
Goodwill and Permits and other intangibles, net	133,908				139,741				133,908	139,741
Assets	847,994				862,957				847,994	862,957	800,060
Industrial and Field Services
Total revenues									593,722	582,215	989,953
Property, plant and equipment, net	254,091				245,143				254,091	245,143
Permits and other intangibles, net	17,049				17,817				17,049	17,817
Goodwill	112,253				107,968				112,253	107,968	105,286
Goodwill and Permits and other intangibles, net	129,302				125,785				129,302	125,785
Assets	464,142				446,826				464,142	446,826	461,180
Safety-Kleen
Total revenues									1,087,886	996,083	941,689
Property, plant and equipment, net	582,162				584,647				582,162	584,647
Permits and other intangibles, net	371,609				391,390				371,609	391,390
Goodwill	306,137				296,070				306,137	296,070	266,344
Goodwill and Permits and other intangibles, net	677,746				687,460				677,746	687,460
Assets	1,471,291				1,474,755				1,471,291	1,474,755	1,297,971
Oil, Gas and Lodging Services
Total revenues									119,603	119,883	207,139
Property, plant and equipment, net	168,294				182,038				168,294	182,038
Permits and other intangibles, net	6,695				10,889				6,695	10,889
Goodwill	0				0				0	0	32,208
Goodwill and Permits and other intangibles, net	6,695				10,889				6,695	10,889
Assets	229,105				253,242				229,105	253,242	333,245
Corporate Items
Property, plant and equipment, net	78,064				78,865				78,064	78,865
Assets	694,038				644,140				694,038	644,140	538,972
United States and Puerto Rico
Total revenues									$ 2,392,000	$ 2,213,400	$ 2,576,200
Percent of revenues									81.20%	80.30%	78.70%
United States
Assets	2,985,394				2,960,337				$ 2,985,394	$ 2,960,337	$ 2,575,746
Canada
Total revenues									$ 552,100	$ 538,000	$ 695,000
Percent of revenues									18.70%	19.50%	21.20%
Property, plant and equipment, net	$ 411,900				$ 400,300				$ 411,900	$ 400,300
Percent of property, plant and equipment, net	26.00%				24.80%				26.00%	24.80%
Permits and other intangibles, net	$ 60,500				$ 63,100				$ 60,500	$ 63,100
Percent of permits and other intangibles, net	12.90%				12.70%				12.90%	12.70%
Assets	$ 721,176				$ 721,583				$ 721,176	$ 721,583	$ 851,949
Other foreign
Percent of revenues									0.10%		0.10%
Assets	$ 0				$ 0				$ 0	$ 0	$ 3,733

GUARANTOR AND NON-GUARANTOR 111

GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Balance Sheet) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Guarantor and Non-Guarantor Subsidiaries Financial Information [Abstract]
Guarantor, ownership interest by Clean Harbors, Inc.	100.00%
Assets:
Cash and cash equivalents	$ 319,399	$ 306,997	$ 184,708	$ 246,879
Short-term marketable securities	38,179	0
Intercompany receivables	0	0
Accounts receivable, net	528,924	496,226
Other current assets	267,554	289,648
Property, plant and equipment, net	1,587,365	1,611,827
Investments in subsidiaries	0	0
Intercompany debt receivable	0	0
Goodwill	478,523	465,154	453,105
Permits and other intangibles, net	469,128	498,721
Other long-term assets	17,498	13,347
Total assets	3,706,570	3,681,920	3,431,428
Liabilities and Stockholders' Equity:
Current liabilities	503,817	504,668
Intercompany payables	0	0
Closure, post-closure and remedial liabilities, net	165,723	166,322
Long-term obligations, less current portion	1,625,537	1,633,272
Intercompany debt payable	0	0
Other long-term liabilities	223,291	293,417
Total liabilities	2,518,368	2,597,679
Stockholders' equity	1,188,202	1,084,241	1,096,282	1,262,871
Total liabilities and stockholders' equity	3,706,570	3,681,920
Reportable Legal Entities | Clean Harbors, Inc.
Assets:
Cash and cash equivalents	51,638	51,417	11,017	1,006
Short-term marketable securities	0
Intercompany receivables	238,339	200,337
Accounts receivable, net	0	0
Other current assets	897	3,096
Property, plant and equipment, net	0	0
Investments in subsidiaries	3,112,547	2,851,571
Intercompany debt receivable	0	0
Goodwill	0	0
Permits and other intangibles, net	0	0
Other long-term assets	2,084	2,446
Total assets	3,405,505	3,108,867
Liabilities and Stockholders' Equity:
Current liabilities	16,954	21,805
Intercompany payables	574,812	365,848
Closure, post-closure and remedial liabilities, net	0	0
Long-term obligations, less current portion	1,625,537	1,633,272
Intercompany debt payable	0	3,701
Other long-term liabilities	0	0
Total liabilities	2,217,303	2,024,626
Stockholders' equity	1,188,202	1,084,241
Total liabilities and stockholders' equity	3,405,505	3,108,867
Reportable Legal Entities | Guarantor Subsidiaries
Assets:
Cash and cash equivalents	207,777	155,943	83,479	154,147
Short-term marketable securities	0
Intercompany receivables	590,100	354,836
Accounts receivable, net	433,042	417,029
Other current assets	233,602	234,408
Property, plant and equipment, net	1,174,975	1,211,210
Investments in subsidiaries	569,568	580,124
Intercompany debt receivable	92,530	86,409
Goodwill	415,641	412,638
Permits and other intangibles, net	408,655	435,594
Other long-term assets	12,064	7,582
Total assets	4,137,954	3,895,773
Liabilities and Stockholders' Equity:
Current liabilities	371,135	366,831
Intercompany payables	289,531	237,058
Closure, post-closure and remedial liabilities, net	148,872	150,682
Long-term obligations, less current portion	0	0
Intercompany debt payable	21,000	21,000
Other long-term liabilities	201,086	275,649
Total liabilities	1,031,624	1,051,220
Stockholders' equity	3,106,330	2,844,553
Total liabilities and stockholders' equity	4,137,954	3,895,773
Reportable Legal Entities | Non-Guarantor Subsidiaries
Assets:
Cash and cash equivalents	59,984	99,637	90,212	91,726
Short-term marketable securities	38,179
Intercompany receivables	52,909	49,055
Accounts receivable, net	95,882	79,197
Other current assets	52,947	69,257
Property, plant and equipment, net	412,390	400,617
Investments in subsidiaries	0	0
Intercompany debt receivable	21,000	24,701
Goodwill	62,882	52,516
Permits and other intangibles, net	60,473	63,127
Other long-term assets	3,350	4,387
Total assets	859,996	842,494
Liabilities and Stockholders' Equity:
Current liabilities	135,620	133,145
Intercompany payables	17,005	1,322
Closure, post-closure and remedial liabilities, net	16,851	15,640
Long-term obligations, less current portion	0	0
Intercompany debt payable	92,530	86,409
Other long-term liabilities	22,205	18,836
Total liabilities	284,211	255,352
Stockholders' equity	575,785	587,142
Total liabilities and stockholders' equity	859,996	842,494
Consolidating Adjustments
Assets:
Cash and cash equivalents	0	0	$ 0	$ 0
Short-term marketable securities	0
Intercompany receivables	(881,348)	(604,228)
Accounts receivable, net	0	0
Other current assets	(19,892)	(17,113)
Property, plant and equipment, net	0	0
Investments in subsidiaries	(3,682,115)	(3,431,695)
Intercompany debt receivable	(113,530)	(111,110)
Goodwill	0	0
Permits and other intangibles, net	0	0
Other long-term assets	0	(1,068)
Total assets	(4,696,885)	(4,165,214)
Liabilities and Stockholders' Equity:
Current liabilities	(19,892)	(17,113)
Intercompany payables	(881,348)	(604,228)
Closure, post-closure and remedial liabilities, net	0	0
Long-term obligations, less current portion	0	0
Intercompany debt payable	(113,530)	(111,110)
Other long-term liabilities	0	(1,068)
Total liabilities	(1,014,770)	(733,519)
Stockholders' equity	(3,682,115)	(3,431,695)
Total liabilities and stockholders' equity	$ (4,696,885)	$ (4,165,214)

GUARANTOR AND NON-GUARANTOR 112

GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Income Statement) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues
Service revenues									$ 2,398,650	$ 2,280,809	$ 2,744,272
Product revenues									546,328	474,417	530,865
Total revenues	$ 747,403	$ 755,846	$ 752,788	$ 688,941	$ 692,113	$ 729,520	$ 697,510	$ 636,083	2,944,978	2,755,226	3,275,137
Cost of revenues (exclusive of items shown separately below)
Service cost of revenues									1,641,798	1,543,210	1,898,907
Product cost of revenues									420,875	389,647	457,899
Total cost of revenues	526,690	519,595	519,803	496,585	496,661	491,915	480,002	464,279	2,062,673	1,932,857	2,356,806
Selling, general and administrative expenses									456,648	422,015	414,164
Accretion of environmental liabilities									9,460	10,177	10,402
Depreciation and amortization									288,422	287,002	274,194
Goodwill impairment charges						34,000			0	34,013	31,992
Income (loss) from operations	27,935	47,663	46,744	5,433	21,943	16,802	34,504	(4,087)	127,775	69,162	187,579
Other (expense) income, net	(3,305)	(432)	(833)	(1,549)	6,932	(198)	(189)	(350)	(6,119)	6,195	(1,380)
Loss on early extinguishment of debt		(1,900)	(6,000)						(7,891)	0	0
Gain on sale of businesses			31,700			16,400			30,732	16,884	0
Interest (expense) income, net									(85,808)	(83,525)	(76,553)
Equity in earnings of subsidiaries, net of tax									0	0	0
Intercompany interest income (expense)									0	0	0
Income (loss) before (benefit) provision for income taxes									58,689	8,716	109,646
(Benefit) provision for income taxes									(42,050)	48,589	65,544
Net income (loss)	$ 84,194	$ 12,058	$ 25,880	$ (21,393)	$ (12,713)	$ (10,255)	$ 3,966	$ (20,871)	100,739	(39,873)	44,102
Other comprehensive income									41,919	40,566	(144,050)
Comprehensive income (loss)									142,658	693	(99,948)
Reportable Legal Entities | Clean Harbors, Inc.
Revenues
Service revenues									0	0	0
Product revenues									0	0	0
Total revenues									0	0	0
Cost of revenues (exclusive of items shown separately below)
Service cost of revenues									0	0	5
Product cost of revenues									0	0	0
Total cost of revenues									0	0	5
Selling, general and administrative expenses									0	85	101
Accretion of environmental liabilities									0	0	0
Depreciation and amortization									0	0	0
Goodwill impairment charges										0	0
Income (loss) from operations									0	(85)	(106)
Other (expense) income, net									(222)	0	0
Loss on early extinguishment of debt									(7,891)
Gain on sale of businesses									0	0
Interest (expense) income, net									(87,113)	(88,984)	(78,621)
Equity in earnings of subsidiaries, net of tax									157,963	13,568	91,339
Intercompany interest income (expense)									0	0	0
Income (loss) before (benefit) provision for income taxes									62,737	(75,501)	12,612
(Benefit) provision for income taxes									(38,002)	(35,628)	(31,490)
Net income (loss)									100,739	(39,873)	44,102
Other comprehensive income									41,919	40,566	(144,050)
Comprehensive income (loss)									142,658	693	(99,948)
Reportable Legal Entities | Guarantor Subsidiaries
Revenues
Service revenues									1,870,256	1,747,985	2,111,086
Product revenues									492,036	410,868	458,314
Total revenues									2,362,292	2,158,853	2,569,400
Cost of revenues (exclusive of items shown separately below)
Service cost of revenues									1,224,326	1,116,132	1,415,435
Product cost of revenues									386,455	349,069	410,128
Total cost of revenues									1,610,781	1,465,201	1,825,563
Selling, general and administrative expenses									373,050	341,963	329,069
Accretion of environmental liabilities									8,479	9,261	9,209
Depreciation and amortization									205,034	201,153	184,017
Goodwill impairment charges										0	4,164
Income (loss) from operations									164,948	141,275	217,378
Other (expense) income, net									(5,156)	7,713	491
Loss on early extinguishment of debt									0
Gain on sale of businesses									30,732	1,704
Interest (expense) income, net									1,523	5,391	1,860
Equity in earnings of subsidiaries, net of tax									(48,683)	(80,244)	(47,141)
Intercompany interest income (expense)									5,288	19,855	23,156
Income (loss) before (benefit) provision for income taxes									148,652	95,694	195,744
(Benefit) provision for income taxes									(10,117)	82,643	104,405
Net income (loss)									158,769	13,051	91,339
Other comprehensive income									41,919	40,566	(144,050)
Comprehensive income (loss)									200,688	53,617	(52,711)
Reportable Legal Entities | Non-Guarantor Subsidiaries
Revenues
Service revenues									582,042	582,075	692,216
Product revenues									66,511	73,793	83,970
Total revenues									648,553	655,868	776,186
Cost of revenues (exclusive of items shown separately below)
Service cost of revenues									471,120	476,329	542,497
Product cost of revenues									46,639	50,822	59,190
Total cost of revenues									517,759	527,151	601,687
Selling, general and administrative expenses									83,598	79,967	84,994
Accretion of environmental liabilities									981	916	1,193
Depreciation and amortization									83,388	85,849	90,177
Goodwill impairment charges										34,013	27,828
Income (loss) from operations									(37,173)	(72,028)	(29,693)
Other (expense) income, net									(741)	(1,518)	(1,871)
Loss on early extinguishment of debt									0
Gain on sale of businesses									0	15,180
Interest (expense) income, net									(218)	68	208
Equity in earnings of subsidiaries, net of tax									0	0	0
Intercompany interest income (expense)									(5,288)	(19,855)	(23,156)
Income (loss) before (benefit) provision for income taxes									(43,420)	(78,153)	(54,512)
(Benefit) provision for income taxes									6,069	1,574	(7,371)
Net income (loss)									(49,489)	(79,727)	(47,141)
Other comprehensive income									38,131	15,291	(93,983)
Comprehensive income (loss)									(11,358)	(64,436)	(141,124)
Consolidating Adjustments
Revenues
Service revenues									(53,648)	(49,251)	(59,030)
Product revenues									(12,219)	(10,244)	(11,419)
Total revenues									(65,867)	(59,495)	(70,449)
Cost of revenues (exclusive of items shown separately below)
Service cost of revenues									(53,648)	(49,251)	(59,030)
Product cost of revenues									(12,219)	(10,244)	(11,419)
Total cost of revenues									(65,867)	(59,495)	(70,449)
Selling, general and administrative expenses									0	0	0
Accretion of environmental liabilities									0	0	0
Depreciation and amortization									0	0	0
Goodwill impairment charges										0	0
Income (loss) from operations									0	0	0
Other (expense) income, net									0	0	0
Loss on early extinguishment of debt									0
Gain on sale of businesses									0	0
Interest (expense) income, net									0	0	0
Equity in earnings of subsidiaries, net of tax									(109,280)	66,676	(44,198)
Intercompany interest income (expense)									0	0	0
Income (loss) before (benefit) provision for income taxes									(109,280)	66,676	(44,198)
(Benefit) provision for income taxes									0	0	0
Net income (loss)									(109,280)	66,676	(44,198)
Other comprehensive income									(80,050)	(55,857)	238,033
Comprehensive income (loss)									$ (189,330)	$ 10,819	$ 193,835

GUARANTOR AND NON-GUARANTOR 113

GUARANTOR AND NON-GUARANTOR SUBSIDIARIES (Cash Flows) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed consolidating statement of cash flows
Net cash from operating activities	$ 285,698	$ 259,624	$ 396,383
Cash flows used in investing activities:
Additions to property, plant and equipment	(167,007)	(219,384)	(257,196)
Proceeds from sale and disposal of fixed assets	7,124	20,817	6,195
Proceeds from sale of investments	376	0	0
Acquisitions, net of cash acquired	(49,227)	(206,915)	(94,345)
Proceeds on sale of businesses, net of transactional costs	45,426	47,134	0
Additions to intangible assets including costs to obtain or renew permits	(1,617)	(2,831)	(5,296)
Purchases of available-for-sale securities	(38,342)	(598)	0
Investment in subsidiaries		0
Intercompany	0	0	0
Intercompany debt	0	0	0
Net cash used in investing activities	(203,267)	(361,777)	(350,642)
Cash flows (used in) from financing activities:
Change in uncashed checks	(5,940)	(3,177)	(14,630)
Proceeds from exercise of stock options	46	627	397
Tax payments related to withholdings on vested restricted stock	(3,149)	(2,819)	(2,159)
Excess tax benefit of stock-based compensation	0	1,198	71
Deferred financing costs paid	(5,718)	(4,031)	0
Repurchases of common stock	(48,971)	(22,188)	(73,347)
Payments on capital leases	0	0	(511)
Principal payment on debt	(402,000)	0	0
Premiums paid on early extinguishment of debt	(6,028)	0	0
Issuance of senior secured notes, net of discount	399,000	0	0
Issuance of senior unsecured notes, including premium	0	250,625	0
Intercompany	0	0	0
Intercompany debt	0	0	0
Net cash (used in) from financing activities	(72,760)	220,235	(90,179)
Effect of exchange rate change on cash	2,731	4,207	(17,733)
Increase (decrease) in cash and cash equivalents	12,402	122,289	(62,171)
Cash and cash equivalents, beginning of year	306,997	184,708	246,879
Cash and cash equivalents, end of year	319,399	306,997	184,708
Guarantor Subsidiaries
Cash flows used in investing activities:
Proceeds from sale of investments	0
Reportable Legal Entities | Clean Harbors, Inc.
Condensed consolidating statement of cash flows
Net cash from operating activities	16,292	51,033	9,543
Cash flows used in investing activities:
Additions to property, plant and equipment	0	0	0
Proceeds from sale and disposal of fixed assets	0	0	0
Proceeds from sale of investments	376
Acquisitions, net of cash acquired	0	0	0
Proceeds on sale of businesses, net of transactional costs	0	0
Additions to intangible assets including costs to obtain or renew permits	0	0	0
Purchases of available-for-sale securities	0	(102)
Investment in subsidiaries		(257,125)
Intercompany	0	0	0
Intercompany debt	0	0	0
Net cash used in investing activities	376	(257,227)	0
Cash flows (used in) from financing activities:
Change in uncashed checks	0	0	0
Proceeds from exercise of stock options	46	627	397
Tax payments related to withholdings on vested restricted stock	(3,149)	(2,819)	(2,159)
Excess tax benefit of stock-based compensation		1,198	71
Deferred financing costs paid	(5,718)	(4,031)
Repurchases of common stock	(48,971)	(22,188)	(73,347)
Payments on capital leases			0
Principal payment on debt	(402,000)
Premiums paid on early extinguishment of debt	(6,028)
Issuance of senior secured notes, net of discount	399,000
Issuance of senior unsecured notes, including premium		250,625
Intercompany	54,074	23,182	75,506
Intercompany debt	(3,701)	0	0
Net cash (used in) from financing activities	(16,447)	246,594	468
Effect of exchange rate change on cash	0	0	0
Increase (decrease) in cash and cash equivalents	221	40,400	10,011
Cash and cash equivalents, beginning of year	51,417	11,017	1,006
Cash and cash equivalents, end of year	51,638	51,417	11,017
Reportable Legal Entities | Guarantor Subsidiaries
Condensed consolidating statement of cash flows
Net cash from operating activities	217,001	125,591	314,585
Cash flows used in investing activities:
Additions to property, plant and equipment	(142,211)	(194,184)	(220,789)
Proceeds from sale and disposal of fixed assets	1,979	12,926	1,447
Acquisitions, net of cash acquired	(11,427)	(196,915)	(94,345)
Proceeds on sale of businesses, net of transactional costs	45,245	18,885
Additions to intangible assets including costs to obtain or renew permits	(1,153)	(1,749)	0
Purchases of available-for-sale securities	0	0
Investment in subsidiaries		0
Intercompany	(54,074)	(23,182)	(75,506)
Intercompany debt	0	63,118	14,272
Net cash used in investing activities	(161,641)	(321,101)	(374,921)
Cash flows (used in) from financing activities:
Change in uncashed checks	(3,526)	(3,651)	(10,129)
Proceeds from exercise of stock options	0	0	0
Tax payments related to withholdings on vested restricted stock	0	0	0
Excess tax benefit of stock-based compensation		0	0
Deferred financing costs paid	0	0
Repurchases of common stock	0	0	0
Payments on capital leases			(203)
Principal payment on debt	0
Premiums paid on early extinguishment of debt	0
Issuance of senior secured notes, net of discount	0
Issuance of senior unsecured notes, including premium		250,625
Intercompany	0	0	0
Intercompany debt	0	21,000	0
Net cash (used in) from financing activities	(3,526)	267,974	(10,332)
Effect of exchange rate change on cash	0	0	0
Increase (decrease) in cash and cash equivalents	51,834	72,464	(70,668)
Cash and cash equivalents, beginning of year	155,943	83,479	154,147
Cash and cash equivalents, end of year	207,777	155,943	83,479
Reportable Legal Entities | Non-Guarantor Subsidiaries
Condensed consolidating statement of cash flows
Net cash from operating activities	52,405	83,000	72,255
Cash flows used in investing activities:
Additions to property, plant and equipment	(24,796)	(25,200)	(36,407)
Proceeds from sale and disposal of fixed assets	5,145	7,891	4,748
Proceeds from sale of investments	0
Acquisitions, net of cash acquired	(37,800)	(10,000)	0
Proceeds on sale of businesses, net of transactional costs	181	28,249
Additions to intangible assets including costs to obtain or renew permits	(464)	(1,082)	(5,296)
Purchases of available-for-sale securities	(38,342)	(496)
Investment in subsidiaries		0
Intercompany	0	0	0
Intercompany debt	3,701	(21,000)	0
Net cash used in investing activities	(92,375)	(21,638)	(36,955)
Cash flows (used in) from financing activities:
Change in uncashed checks	(2,414)	474	(4,501)
Proceeds from exercise of stock options	0	0	0
Tax payments related to withholdings on vested restricted stock	0	0	0
Excess tax benefit of stock-based compensation		0	0
Deferred financing costs paid	0	0
Repurchases of common stock	0	0	0
Payments on capital leases			(308)
Principal payment on debt	0
Premiums paid on early extinguishment of debt	0
Issuance of senior secured notes, net of discount	0
Issuance of senior unsecured notes, including premium		0
Intercompany	0	6,500	0
Intercompany debt	0	(63,118)	(14,272)
Net cash (used in) from financing activities	(2,414)	(56,144)	(19,081)
Effect of exchange rate change on cash	2,731	4,207	(17,733)
Increase (decrease) in cash and cash equivalents	(39,653)	9,425	(1,514)
Cash and cash equivalents, beginning of year	99,637	90,212	91,726
Cash and cash equivalents, end of year	59,984	99,637	90,212
Consolidating Adjustments
Condensed consolidating statement of cash flows
Net cash from operating activities	0	0	0
Cash flows used in investing activities:
Additions to property, plant and equipment	0	0	0
Proceeds from sale and disposal of fixed assets	0	0	0
Proceeds from sale of investments	0
Acquisitions, net of cash acquired	0	0	0
Proceeds on sale of businesses, net of transactional costs	0	0
Additions to intangible assets including costs to obtain or renew permits	0	0	0
Purchases of available-for-sale securities	0	0
Investment in subsidiaries		257,125
Intercompany	54,074	23,182	75,506
Intercompany debt	(3,701)	(42,118)	(14,272)
Net cash used in investing activities	50,373	238,189	61,234
Cash flows (used in) from financing activities:
Change in uncashed checks	0	0	0
Proceeds from exercise of stock options	0	0	0
Tax payments related to withholdings on vested restricted stock	0	0	0
Excess tax benefit of stock-based compensation		0	0
Deferred financing costs paid	0	0
Repurchases of common stock	0	0	0
Payments on capital leases			0
Principal payment on debt	0
Premiums paid on early extinguishment of debt	0
Issuance of senior secured notes, net of discount	0
Issuance of senior unsecured notes, including premium		(250,625)
Intercompany	(54,074)	(29,682)	(75,506)
Intercompany debt	3,701	42,118	14,272
Net cash (used in) from financing activities	(50,373)	(238,189)	(61,234)
Effect of exchange rate change on cash	0	0	0
Increase (decrease) in cash and cash equivalents	0	0	0
Cash and cash equivalents, beginning of year	0	0	0
Cash and cash equivalents, end of year	$ 0	$ 0	$ 0

QUARTERLY DATA (UNAUDITED) (Det

QUARTERLY DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 747,403	$ 755,846	$ 752,788	$ 688,941	$ 692,113	$ 729,520	$ 697,510	$ 636,083	$ 2,944,978	$ 2,755,226	$ 3,275,137
Cost of revenues	526,690	519,595	519,803	496,585	496,661	491,915	480,002	464,279	2,062,673	1,932,857	2,356,806
(Loss) income from operations	27,935	47,663	46,744	5,433	21,943	16,802	34,504	(4,087)	127,775	69,162	187,579
Other (expense) income, net	(3,305)	(432)	(833)	(1,549)	6,932	(198)	(189)	(350)	(6,119)	6,195	(1,380)
Net (loss) income	$ 84,194	$ 12,058	$ 25,880	$ (21,393)	$ (12,713)	$ (10,255)	$ 3,966	$ (20,871)	$ 100,739	$ (39,873)	$ 44,102
Basic (loss) earnings per share (in dollars per share)	$ 1.48	$ 0.21	$ 0.45	$ (0.37)	$ (0.22)	$ (0.18)	$ 0.07	$ (0.36)	$ 1.77	$ (0.69)	$ 0.76
Diluted (loss) earnings per share (in dollars per share)	$ 1.48	$ 0.21	$ 0.45	$ (0.37)	$ (0.22)	$ (0.18)	$ 0.07	$ (0.36)	$ 1.76	$ (0.69)	$ 0.76
Goodwill impairment charge						$ 34,000			$ 0	$ 34,013	$ 31,992
Gain on sale of businesses			$ 31,700			$ 16,400			30,732	16,884	0
Loss on early extinguishment of debt		$ 1,900	$ 6,000						$ 7,891	$ 0	$ 0
Tax benefit due to reduction in net deferred tax liability	$ 93,000

SUBSEQUENT EVENTS Subsequent Ev

SUBSEQUENT EVENTS Subsequent Events (Details)	Feb. 23, 2018USD ($)
Subsequent Event
Subsequent Event [Line Items]
Payments to acquire businesses, gross	$ 120,000,000

SCHEDULE II VALUATION AND QU116

SCHEDULE II VALUATION AND QUALIFYING ACCOUNTS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Doubtful Accounts
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance Beginning of Period	$ 15,046	$ 15,194	$ 13,476
Additions Charged to Operating Expense	7,901	6,907	4,793
Deductions from Reserves	6,774	7,055	3,075
Balance End of Period	16,173	15,046	15,194
Revenue Allowance
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance Beginning of Period	14,203	16,232	12,185
Additions Charged to Operating Expense	24,862	24,252	28,312
Deductions from Reserves	27,439	26,281	24,265
Balance End of Period	11,626	14,203	16,232
Valuation Allowance on Deferred Tax Assets
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance Beginning of Period	55,189	30,916	29,061
Additions Charged to Operating Expense	9,052	22,564	2,274
Deductions from Reserves	4,114	1,709	(419)
Balance End of Period	$ 68,355	$ 55,189	$ 30,916