SEGMENT REPORTING - Reconciliation of Third Party Revenues to Direct Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Segment Reporting Information [Line Items]
Total revenues	$ 926,458	$ 710,000	$ 1,734,606	$ 1,568,563
Environmental Services
Segment Reporting Information [Line Items]
Total revenues	724,097	612,594	1,378,699	1,317,786
Safety-Kleen Sustainability Solutions
Segment Reporting Information [Line Items]
Total revenues	202,282	97,350	355,749	250,631
Operating Segments [Member] | Environmental Services
Segment Reporting Information [Line Items]
Total revenues	723,147	612,720	1,376,025	1,317,756
Operating Segments [Member] | Safety-Kleen Sustainability Solutions
Segment Reporting Information [Line Items]
Total revenues	203,232	97,224	358,423	250,661
Intersegment revenues, net | Environmental Services
Segment Reporting Information [Line Items]
Total revenues	950	(126)	2,674	30
Intersegment revenues, net | Safety-Kleen Sustainability Solutions
Segment Reporting Information [Line Items]
Total revenues	(950)	126	(2,674)	(30)
Corporate, non-Segment
Segment Reporting Information [Line Items]
Total revenues	79	56	158	146
Operating and Corporate non-segment
Segment Reporting Information [Line Items]
Total revenues	$ 79	$ 56	$ 158	$ 146