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