REVENUES - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Total third party revenues	$ 891,668	$ 843,181	$ 2,541,185	$ 2,442,099
Technical Services
Disaggregation of Revenue [Line Items]
Total third party revenues	292,506	264,769	820,333	758,081
Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total third party revenues	95,546	77,025	253,894	223,052
Industrial Services
Disaggregation of Revenue [Line Items]
Total third party revenues	131,855	134,323	383,964	399,132
Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Total third party revenues	30,344	33,163	92,848	89,300
Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total third party revenues	217,439	200,681	640,956	594,876
Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total third party revenues	123,978	133,220	349,190	377,658
United States
Disaggregation of Revenue [Line Items]
Total third party revenues	764,352	718,223	2,188,327	2,064,531
Canada
Disaggregation of Revenue [Line Items]
Total third party revenues	127,316	124,958	352,858	377,568
Environmental Services
Disaggregation of Revenue [Line Items]
Total third party revenues	586,872	542,980	1,658,970	1,570,241
Safety-Kleen
Disaggregation of Revenue [Line Items]
Total third party revenues	306,145	300,885	884,606	873,284
Operating segments | Environmental Services
Disaggregation of Revenue [Line Items]
Total third party revenues	550,122	508,813	1,550,114	1,468,417
Operating segments | Environmental Services | Technical Services
Disaggregation of Revenue [Line Items]
Total third party revenues	292,506	264,769	820,333	758,081
Operating segments | Environmental Services | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total third party revenues	95,546	77,025	253,894	223,052
Operating segments | Environmental Services | Industrial Services
Disaggregation of Revenue [Line Items]
Total third party revenues	131,855	134,323	383,964	399,132
Operating segments | Environmental Services | Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Total third party revenues	30,215	32,696	91,923	88,152
Operating segments | Environmental Services | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0	0	0
Operating segments | Environmental Services | Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0	0	0
Operating segments | Environmental Services | United States
Disaggregation of Revenue [Line Items]
Total third party revenues	450,638	410,792	1,270,556	1,162,891
Operating segments | Environmental Services | Canada
Disaggregation of Revenue [Line Items]
Total third party revenues	99,484	98,021	279,558	305,526
Operating segments | Safety-Kleen
Disaggregation of Revenue [Line Items]
Total third party revenues	341,417	333,901	990,146	972,534
Operating segments | Safety-Kleen | Technical Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0	0	0
Operating segments | Safety-Kleen | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0	0	0
Operating segments | Safety-Kleen | Industrial Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0	0	0
Operating segments | Safety-Kleen | Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0	0	0
Operating segments | Safety-Kleen | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total third party revenues	217,439	200,681	640,956	594,876
Operating segments | Safety-Kleen | Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total third party revenues	123,978	133,220	349,190	377,658
Operating segments | Safety-Kleen | United States
Disaggregation of Revenue [Line Items]
Total third party revenues	313,979	307,497	917,240	901,198
Operating segments | Safety-Kleen | Canada
Disaggregation of Revenue [Line Items]
Total third party revenues	27,438	26,404	72,906	71,336
Corporate Items
Disaggregation of Revenue [Line Items]
Total third party revenues	129	467	925	1,148
Corporate Items | Technical Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0	0	0
Corporate Items | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0	0	0
Corporate Items | Industrial Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0	0	0
Corporate Items | Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Total third party revenues	129	467	925	1,148
Corporate Items | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0	0	0
Corporate Items | Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0	0	0
Corporate Items | United States
Disaggregation of Revenue [Line Items]
Total third party revenues	(265)	(66)	531	442
Corporate Items | Canada
Disaggregation of Revenue [Line Items]
Total third party revenues	$ 394	$ 533	$ 394	$ 706