SEGMENT REPORTING - Reconciliation of Third Party Revenues to Direct Revenues (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Segment Reporting Information [Line Items]
Total revenues	$ 1,169,109	$ 808,148
Environmental Services
Segment Reporting Information [Line Items]
Total revenues	947,445	654,602
Safety-Kleen Sustainability Solutions
Segment Reporting Information [Line Items]
Total revenues	221,592	153,467
Operating Segments | Environmental Services
Segment Reporting Information [Line Items]
Total revenues	940,798	652,878
Operating Segments | Safety-Kleen Sustainability Solutions
Segment Reporting Information [Line Items]
Total revenues	228,239	155,191
Intersegment revenues, net | Environmental Services
Segment Reporting Information [Line Items]
Total revenues	6,647	1,724
Intersegment revenues, net | Safety-Kleen Sustainability Solutions
Segment Reporting Information [Line Items]
Total revenues	(6,647)	(1,724)
Corporate
Segment Reporting Information [Line Items]
Total revenues	72	79
Operating and Corporate non-segment
Segment Reporting Information [Line Items]
Total revenues	$ 72	$ 79