REVENUES - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Total revenues	$ 3,805,566	$ 3,144,097	$ 3,412,190
Technical Services
Disaggregation of Revenue [Line Items]
Total revenues	1,209,624	1,062,714	1,120,043
Field and Emergency Response
Disaggregation of Revenue [Line Items]
Total revenues	466,380	461,036	340,906
Field and Emergency Response | HydroChemPSC
Disaggregation of Revenue [Line Items]
Total revenues	28,400
Industrial Services And Other
Disaggregation of Revenue [Line Items]
Total revenues	706,298	480,621	632,550
Industrial Services And Other | HydroChemPSC
Disaggregation of Revenue [Line Items]
Total revenues	137,700
Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total revenues	805,491	809,236	851,520
Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total revenues	617,773	330,490	467,171
United States
Disaggregation of Revenue [Line Items]
Total revenues	3,324,953	2,739,557	2,940,832
Canada
Disaggregation of Revenue [Line Items]
Total revenues	480,613	404,540	471,358
Environmental Services
Disaggregation of Revenue [Line Items]
Total revenues	3,032,454	2,635,901	2,795,994
Safety-Kleen Sustainability Solutions
Disaggregation of Revenue [Line Items]
Total revenues	772,813	507,906	615,060
Operating segments | Environmental Services
Disaggregation of Revenue [Line Items]
Total revenues	3,025,907	2,637,641	2,802,682
Operating segments | Environmental Services | Technical Services
Disaggregation of Revenue [Line Items]
Total revenues	1,209,624	1,062,714	1,120,043
Operating segments | Environmental Services | Field and Emergency Response
Disaggregation of Revenue [Line Items]
Total revenues	466,380	461,036	340,906
Operating segments | Environmental Services | Industrial Services And Other
Disaggregation of Revenue [Line Items]
Total revenues	705,999	480,331	631,414
Operating segments | Environmental Services | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total revenues	643,904	633,560	710,319
Operating segments | Environmental Services | Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0
Operating segments | Environmental Services | United States
Disaggregation of Revenue [Line Items]
Total revenues	2,631,112	2,287,796	2,390,718
Operating segments | Environmental Services | Canada
Disaggregation of Revenue [Line Items]
Total revenues	394,795	349,845	411,964
Operating segments | Safety-Kleen Sustainability Solutions
Disaggregation of Revenue [Line Items]
Total revenues	779,360	506,166	608,372
Operating segments | Safety-Kleen Sustainability Solutions | Technical Services
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0
Operating segments | Safety-Kleen Sustainability Solutions | Field and Emergency Response
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0
Operating segments | Safety-Kleen Sustainability Solutions | Industrial Services And Other
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0
Operating segments | Safety-Kleen Sustainability Solutions | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total revenues	161,587	175,676	141,201
Operating segments | Safety-Kleen Sustainability Solutions | Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total revenues	617,773	330,490	467,171
Operating segments | Safety-Kleen Sustainability Solutions | United States
Disaggregation of Revenue [Line Items]
Total revenues	693,542	452,435	550,700
Operating segments | Safety-Kleen Sustainability Solutions | Canada
Disaggregation of Revenue [Line Items]
Total revenues	85,818	53,731	57,672
Corporate, non-segment
Disaggregation of Revenue [Line Items]
Total revenues	299	290	1,136
Corporate, non-segment | Technical Services
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0
Corporate, non-segment | Field and Emergency Response
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0
Corporate, non-segment | Industrial Services And Other
Disaggregation of Revenue [Line Items]
Total revenues	299	290	1,136
Corporate, non-segment | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0
Corporate, non-segment | Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0
Corporate, non-segment | United States
Disaggregation of Revenue [Line Items]
Total revenues	299	(674)	(586)
Corporate, non-segment | Canada
Disaggregation of Revenue [Line Items]
Total revenues	$ 0	$ 964	$ 1,722