REVENUES - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Disaggregation of Revenue [Line Items]
Total revenues	$ 1,169,109	$ 808,148
Technical Services
Disaggregation of Revenue [Line Items]
Total revenues	323,656	272,040
Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total revenues	132,359	105,168
Field and Emergency Response Services | HydroChemPSC
Disaggregation of Revenue [Line Items]
Total revenues	28,000
Industrial Services and Other
Disaggregation of Revenue [Line Items]
Total revenues	308,910	119,889
Industrial Services and Other | HydroChemPSC
Disaggregation of Revenue [Line Items]
Total revenues	156,100
Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total revenues	220,333	194,838
Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total revenues	183,851	116,213
United States
Disaggregation of Revenue [Line Items]
Total revenues	1,037,280	714,577
Canada
Disaggregation of Revenue [Line Items]
Total revenues	131,829	93,571
Environmental Services
Disaggregation of Revenue [Line Items]
Total revenues	947,445	654,602
Safety-Kleen Sustainability Solutions
Disaggregation of Revenue [Line Items]
Total revenues	221,592	153,467
Operating segments | Environmental Services
Disaggregation of Revenue [Line Items]
Total revenues	940,798	652,878
Operating segments | Environmental Services | Technical Services
Disaggregation of Revenue [Line Items]
Total revenues	323,656	272,040
Operating segments | Environmental Services | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total revenues	132,359	105,168
Operating segments | Environmental Services | Industrial Services and Other
Disaggregation of Revenue [Line Items]
Total revenues	308,838	119,810
Operating segments | Environmental Services | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total revenues	175,945	155,860
Operating segments | Environmental Services | Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total revenues	0	0
Operating segments | Environmental Services | United States
Disaggregation of Revenue [Line Items]
Total revenues	834,678	575,508
Operating segments | Environmental Services | Canada
Disaggregation of Revenue [Line Items]
Total revenues	106,120	77,370
Operating segments | Safety-Kleen Sustainability Solutions
Disaggregation of Revenue [Line Items]
Total revenues	228,239	155,191
Operating segments | Safety-Kleen Sustainability Solutions | Technical Services
Disaggregation of Revenue [Line Items]
Total revenues	0	0
Operating segments | Safety-Kleen Sustainability Solutions | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total revenues	0	0
Operating segments | Safety-Kleen Sustainability Solutions | Industrial Services and Other
Disaggregation of Revenue [Line Items]
Total revenues	0	0
Operating segments | Safety-Kleen Sustainability Solutions | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total revenues	44,388	38,978
Operating segments | Safety-Kleen Sustainability Solutions | Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total revenues	183,851	116,213
Operating segments | Safety-Kleen Sustainability Solutions | United States
Disaggregation of Revenue [Line Items]
Total revenues	202,530	138,990
Operating segments | Safety-Kleen Sustainability Solutions | Canada
Disaggregation of Revenue [Line Items]
Total revenues	25,709	16,201
Corporate
Disaggregation of Revenue [Line Items]
Total revenues	72	79
Corporate | Technical Services
Disaggregation of Revenue [Line Items]
Total revenues	0	0
Corporate | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total revenues	0	0
Corporate | Industrial Services and Other
Disaggregation of Revenue [Line Items]
Total revenues	72	79
Corporate | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total revenues	0	0
Corporate | Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total revenues	0	0
Corporate | United States
Disaggregation of Revenue [Line Items]
Total revenues	72	79
Corporate | Canada
Disaggregation of Revenue [Line Items]
Total revenues	$ 0	$ 0