SEGMENT REPORTING - Third Party Revenues to Direct Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Total revenues	$ 779,344	$ 891,668	$ 2,347,907	$ 2,541,185
Corporate
Segment Reporting Information [Line Items]
Total revenues	72	129	218	925
Corporate Items, net
Segment Reporting Information [Line Items]
Total revenues	(338)	(1,478)	(2,965)	(3,316)
Operating and Corporate non-segment
Segment Reporting Information [Line Items]
Total revenues	(266)	(1,349)	(2,747)	(2,391)
Environmental Services
Segment Reporting Information [Line Items]
Total revenues	527,970	586,872	1,591,246	1,658,970
Environmental Services | Operating segments
Segment Reporting Information [Line Items]
Total revenues	498,183	550,122	1,490,641	1,550,114
Environmental Services | Intersegment revenues, net
Segment Reporting Information [Line Items]
Total revenues	29,448	35,274	97,782	105,555
Environmental Services | Corporate Items, net
Segment Reporting Information [Line Items]
Total revenues	339	1,476	2,823	3,301
Safety-Kleen
Segment Reporting Information [Line Items]
Total revenues	251,640	306,145	759,408	884,606
Safety-Kleen | Operating segments
Segment Reporting Information [Line Items]
Total revenues	281,089	341,417	857,048	990,146
Safety-Kleen | Intersegment revenues, net
Segment Reporting Information [Line Items]
Total revenues	(29,448)	(35,274)	(97,782)	(105,555)
Safety-Kleen | Corporate Items, net
Segment Reporting Information [Line Items]
Total revenues	$ (1)	$ 2	$ 142	$ 15