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, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Total revenues	$ 871,005	$ 891,668	$ 868,678	$ 780,839	$ 858,204	$ 843,181	$ 849,140	$ 749,778	$ 3,412,190	$ 3,300,303	$ 2,944,978
Adjusted EBITDA									540,317	491,005	425,657
Reconciliation to Consolidated Statements of Operations:
Accretion of environmental liabilities									10,136	9,806	9,460
Depreciation and amortization									300,725	298,625	288,422
(Loss) income from operations	52,307	80,367	73,048	23,734	41,485	65,745	64,353	10,991	229,456	182,574	127,775
Other (income) expense, net	(905)	427	$ 564	$ (2,983)	4,061	996	$ (846)	$ 299	(2,897)	4,510	6,119
Loss on early extinguishment of debt		$ 6,100				$ 2,500			6,131	2,488	7,891
Gain on sale of businesses									(687)	0	(30,732)
Interest expense, net of interest income									78,670	81,094	85,808
(Loss) income before (benefit) provision for income taxes									148,239	94,482	58,689
Assets	4,108,904				3,738,321				4,108,904	3,738,321
Property, plant and equipment, net					1,561,978					1,561,978
Property, plant and equipment, net	1,588,151								1,588,151
Goodwill	525,013				514,189				525,013	514,189	478,523
Permits and other intangibles, net	419,066				441,875				419,066	441,875
Permits and other intangibles, net	944,079				956,064				944,079	956,064
Environmental Services
Segment Reporting Information [Line Items]
Total revenues									2,237,068	2,141,194	1,857,474
Reconciliation to Consolidated Statements of Operations:
Goodwill	212,531				207,019				212,531	207,019	172,386
Safety-Kleen
Segment Reporting Information [Line Items]
Total revenues									1,178,129	1,161,282	1,087,886
Reconciliation to Consolidated Statements of Operations:
Goodwill	312,482				307,170				312,482	307,170	306,137
Operating segments | Environmental Services
Segment Reporting Information [Line Items]
Total revenues									2,092,363	2,003,843	1,728,700
Adjusted EBITDA									446,284	380,856	321,310
Reconciliation to Consolidated Statements of Operations:
Property, plant and equipment, net					951,867					951,867
Property, plant and equipment, net	939,352								939,352
Goodwill	212,531				207,019				212,531	207,019
Permits and other intangibles, net	89,722				93,313				89,722	93,313
Permits and other intangibles, net	302,253				300,332				302,253	300,332
Operating segments | Safety-Kleen
Segment Reporting Information [Line Items]
Total revenues									1,318,691	1,295,355	1,213,703
Adjusted EBITDA									282,378	282,029	249,811
Reconciliation to Consolidated Statements of Operations:
Property, plant and equipment, net					553,220					553,220
Property, plant and equipment, net	555,310								555,310
Goodwill	312,482				307,170				312,482	307,170
Permits and other intangibles, net	329,344				348,562				329,344	348,562
Permits and other intangibles, net	641,826				655,732				641,826	655,732
Intersegment revenues, net | Environmental Services
Segment Reporting Information [Line Items]
Total revenues									140,577	134,104	125,822
Intersegment revenues, net | Safety-Kleen
Segment Reporting Information [Line Items]
Total revenues									(140,577)	(134,104)	(125,822)
Corporate Items, net
Segment Reporting Information [Line Items]
Total revenues									(4,143)	(3,278)	(2,957)
Corporate Items, net | Environmental Services
Segment Reporting Information [Line Items]
Total revenues									4,128	3,247	2,952
Corporate Items, net | Safety-Kleen
Segment Reporting Information [Line Items]
Total revenues									15	31	5
Corporate Items
Segment Reporting Information [Line Items]
Total revenues									1,136	1,105	2,575
Adjusted EBITDA									(188,345)	(171,880)	(145,464)
Reconciliation to Consolidated Statements of Operations:
Property, plant and equipment, net					$ 56,891					56,891
Property, plant and equipment, net	$ 93,489								93,489
Operating segments and corporate non segment
Segment Reporting Information [Line Items]
Total revenues									$ (3,007)	$ (2,173)	$ (382)