REVENUES - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Total third party revenues	$ 868,678	$ 849,140	$ 1,649,517	$ 1,598,918
Technical Services
Disaggregation of Revenue [Line Items]
Total third party revenues	275,908	257,006	527,827	493,312
Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total third party revenues	86,722	76,092	158,348	146,027
Industrial Services
Disaggregation of Revenue [Line Items]
Total third party revenues	136,011	161,046	252,109	264,809
Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Total third party revenues	27,855	26,281	62,504	56,137
Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total third party revenues	216,434	200,034	423,517	394,195
Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total third party revenues	125,748	128,681	225,212	244,438
United States
Disaggregation of Revenue [Line Items]
Total third party revenues	748,639	714,549	1,423,976	1,346,308
Canada
Disaggregation of Revenue [Line Items]
Total third party revenues	120,039	134,591	225,541	252,610
Environmental Services
Disaggregation of Revenue [Line Items]
Total third party revenues	526,294	519,916	999,992	959,604
Environmental Services | Technical Services
Disaggregation of Revenue [Line Items]
Total third party revenues	275,908	257,006	527,827	493,312
Environmental Services | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total third party revenues	86,722	76,092	158,348	146,027
Environmental Services | Industrial Services
Disaggregation of Revenue [Line Items]
Total third party revenues	136,011	161,046	252,109	264,809
Environmental Services | Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Total third party revenues	27,653	25,772	61,708	55,456
Environmental Services | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0	0	0
Environmental Services | Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0	0	0
Environmental Services | United States
Disaggregation of Revenue [Line Items]
Total third party revenues	431,749	408,127	819,918	752,099
Environmental Services | Canada
Disaggregation of Revenue [Line Items]
Total third party revenues	94,545	111,789	180,074	207,505
Safety-Kleen
Disaggregation of Revenue [Line Items]
Total third party revenues	342,182	328,715	648,729	638,633
Safety-Kleen | Technical Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0	0	0
Safety-Kleen | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0	0	0
Safety-Kleen | Industrial Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0	0	0
Safety-Kleen | Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0	0	0
Safety-Kleen | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total third party revenues	216,434	200,034	423,517	394,195
Safety-Kleen | Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total third party revenues	125,748	128,681	225,212	244,438
Safety-Kleen | United States
Disaggregation of Revenue [Line Items]
Total third party revenues	316,688	306,059	603,262	593,701
Safety-Kleen | Canada
Disaggregation of Revenue [Line Items]
Total third party revenues	25,494	22,656	45,467	44,932
Corporate
Disaggregation of Revenue [Line Items]
Total third party revenues	202	509	796	681
Corporate | Technical Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0	0	0
Corporate | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0	0	0
Corporate | Industrial Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0	0	0
Corporate | Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Total third party revenues	202	509	796	681
Corporate | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0	0	0
Corporate | Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0	0	0
Corporate | United States
Disaggregation of Revenue [Line Items]
Total third party revenues	202	363	796	508
Corporate | Canada
Disaggregation of Revenue [Line Items]
Total third party revenues	$ 0	$ 146	$ 0	$ 173