SEGMENT REPORTING (Segment Information, Revenues, EBITA, and Reconciliation to the Consolidated Statement of Operations) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Total revenues	$ 808,148	$ 858,563
Adjusted EBITDA	129,451	125,881
Reconciliation of Net Income to Adjusted EBITDA [Abstract]
Accretion of environmental liabilities	2,953	2,561
Stock-based compensation	3,480	3,291
Depreciation and amortization	72,163	74,533
Income from operations	50,855	45,496
Other expense, net	1,228	2,365
Loss on sale of businesses	0	3,074
Interest expense, net of interest income	17,918	18,787
Income before provision for income taxes	31,709	21,270
Property, plant and equipment, net	1,527,944		$ 1,525,298
Goodwill	543,605		527,023
Permits and other intangibles, net	380,053		386,620
Permits and other intangibles, net	923,658		913,643
Environmental Services
Segment Reporting Information [Line Items]
Total revenues	654,602	705,192
Reconciliation of Net Income to Adjusted EBITDA [Abstract]
Goodwill	402,438		401,918
Safety-Kleen Sustainability Solutions
Segment Reporting Information [Line Items]
Total revenues	153,467	153,281
Reconciliation of Net Income to Adjusted EBITDA [Abstract]
Goodwill	141,167		125,105
Operating segments | Environmental Services
Segment Reporting Information [Line Items]
Total revenues	652,878	705,036
Adjusted EBITDA	140,254	145,858
Reconciliation of Net Income to Adjusted EBITDA [Abstract]
Property, plant and equipment, net	1,056,053		1,068,910
Goodwill	402,438		401,918
Permits and other intangibles, net	224,614		228,237
Permits and other intangibles, net	627,052		630,155
Operating segments | Safety-Kleen Sustainability Solutions
Segment Reporting Information [Line Items]
Total revenues	155,191	153,437
Adjusted EBITDA	31,632	24,204
Reconciliation of Net Income to Adjusted EBITDA [Abstract]
Property, plant and equipment, net	367,689		366,160
Goodwill	141,167		125,105
Permits and other intangibles, net	155,439		158,383
Permits and other intangibles, net	296,606		283,488
Intersegment revenues, net | Environmental Services
Segment Reporting Information [Line Items]
Total revenues	1,724	156
Intersegment revenues, net | Safety-Kleen Sustainability Solutions
Segment Reporting Information [Line Items]
Total revenues	(1,724)	(156)
Corporate, non-Segment
Segment Reporting Information [Line Items]
Total revenues	79	90
Adjusted EBITDA	(42,435)	(44,181)
Reconciliation of Net Income to Adjusted EBITDA [Abstract]
Property, plant and equipment, net	104,202		$ 90,228
Operating and Corporate non-segment
Segment Reporting Information [Line Items]
Total revenues	$ 79	$ 90