REVENUES (Disaggregation of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Total revenues	$ 871,005	$ 891,668	$ 868,678	$ 780,839	$ 858,204	$ 843,181	$ 849,140	$ 749,778	$ 3,412,190	$ 3,300,303	$ 2,944,978
United States
Disaggregation of Revenue [Line Items]
Total revenues									2,940,832	2,796,145
Canada
Disaggregation of Revenue [Line Items]
Total revenues									471,358	504,158
Technical Services
Disaggregation of Revenue [Line Items]
Total revenues									1,120,043	1,037,388
Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total revenues									340,906	304,727
Industrial Services
Disaggregation of Revenue [Line Items]
Total revenues									514,390	541,895
Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Total revenues									118,160	120,938
Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total revenues									851,520	795,077
Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total revenues									467,171	500,278
Environmental Services
Disaggregation of Revenue [Line Items]
Total revenues									2,237,068	2,141,194	1,857,474
Safety-Kleen
Disaggregation of Revenue [Line Items]
Total revenues									1,178,129	1,161,282	1,087,886
Corporate Items
Disaggregation of Revenue [Line Items]
Total revenues										1,105
Corporate Items | United States
Disaggregation of Revenue [Line Items]
Total revenues										1,082
Corporate Items | Canada
Disaggregation of Revenue [Line Items]
Total revenues										23
Corporate Items | Technical Services
Disaggregation of Revenue [Line Items]
Total revenues										0
Corporate Items | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total revenues										0
Corporate Items | Industrial Services
Disaggregation of Revenue [Line Items]
Total revenues										0
Corporate Items | Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Total revenues										1,105
Corporate Items | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total revenues										0
Corporate Items | Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total revenues										0
Operating segments | Environmental Services
Disaggregation of Revenue [Line Items]
Total revenues									2,092,363	2,003,843	1,728,700
Operating segments | Environmental Services | United States
Disaggregation of Revenue [Line Items]
Total revenues									1,721,322	1,598,402
Operating segments | Environmental Services | Canada
Disaggregation of Revenue [Line Items]
Total revenues									371,041	405,441
Operating segments | Environmental Services | Technical Services
Disaggregation of Revenue [Line Items]
Total revenues									1,120,043	1,037,388
Operating segments | Environmental Services | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total revenues									340,906	304,727
Operating segments | Environmental Services | Industrial Services
Disaggregation of Revenue [Line Items]
Total revenues									514,390	541,895
Operating segments | Environmental Services | Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Total revenues									117,024	119,833
Operating segments | Environmental Services | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total revenues									0	0
Operating segments | Environmental Services | Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total revenues									0	0
Operating segments | Safety-Kleen
Disaggregation of Revenue [Line Items]
Total revenues									1,318,691	1,295,355	1,213,703
Operating segments | Safety-Kleen | United States
Disaggregation of Revenue [Line Items]
Total revenues									1,220,096	1,196,661
Operating segments | Safety-Kleen | Canada
Disaggregation of Revenue [Line Items]
Total revenues									98,595	98,694
Operating segments | Safety-Kleen | Technical Services
Disaggregation of Revenue [Line Items]
Total revenues									0	0
Operating segments | Safety-Kleen | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total revenues									0	0
Operating segments | Safety-Kleen | Industrial Services
Disaggregation of Revenue [Line Items]
Total revenues									0	0
Operating segments | Safety-Kleen | Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Total revenues									0	0
Operating segments | Safety-Kleen | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total revenues									851,520	795,077
Operating segments | Safety-Kleen | Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total revenues									467,171	500,278
Corporate, non-segment
Disaggregation of Revenue [Line Items]
Total revenues									1,136	$ 1,105	$ 2,575
Corporate, non-segment | United States
Disaggregation of Revenue [Line Items]
Total revenues									(586)
Corporate, non-segment | Canada
Disaggregation of Revenue [Line Items]
Total revenues									1,722
Corporate, non-segment | Technical Services
Disaggregation of Revenue [Line Items]
Total revenues									0
Corporate, non-segment | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total revenues									0
Corporate, non-segment | Industrial Services
Disaggregation of Revenue [Line Items]
Total revenues									0
Corporate, non-segment | Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Total revenues									1,136
Corporate, non-segment | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total revenues									0
Corporate, non-segment | Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total revenues									$ 0