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