REVENUES (Disaggregation of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Revenues	$ 858,204	$ 843,181	$ 849,140	$ 749,778	$ 747,403	$ 755,846	$ 752,788	$ 688,941	$ 3,300,303	$ 2,944,978	$ 2,755,226
United States
Disaggregation of Revenue [Line Items]
Revenues									2,796,145
Canada
Disaggregation of Revenue [Line Items]
Revenues									504,158
Technical Services
Disaggregation of Revenue [Line Items]
Revenues									1,037,388
Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Revenues									304,727
Industrial Services
Disaggregation of Revenue [Line Items]
Revenues									541,895
Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Revenues									120,938
Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Revenues									795,077
Kleen Performance Products
Disaggregation of Revenue [Line Items]
Revenues									500,278
Environmental Services
Disaggregation of Revenue [Line Items]
Revenues									2,003,843	1,728,700	1,641,432
Environmental Services | United States
Disaggregation of Revenue [Line Items]
Revenues									1,598,402
Environmental Services | Canada
Disaggregation of Revenue [Line Items]
Revenues									405,441
Environmental Services | Technical Services
Disaggregation of Revenue [Line Items]
Revenues									1,037,388
Environmental Services | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Revenues									304,727
Environmental Services | Industrial Services
Disaggregation of Revenue [Line Items]
Revenues									541,895
Environmental Services | Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Revenues									119,833
Environmental Services | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Revenues									0
Environmental Services | Kleen Performance Products
Disaggregation of Revenue [Line Items]
Revenues									0
Safety-Kleen
Disaggregation of Revenue [Line Items]
Revenues									1,295,355	1,213,703	1,110,727
Safety-Kleen | United States
Disaggregation of Revenue [Line Items]
Revenues									1,196,661
Safety-Kleen | Canada
Disaggregation of Revenue [Line Items]
Revenues									98,694
Safety-Kleen | Technical Services
Disaggregation of Revenue [Line Items]
Revenues									0
Safety-Kleen | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Revenues									0
Safety-Kleen | Industrial Services
Disaggregation of Revenue [Line Items]
Revenues									0
Safety-Kleen | Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Revenues									0
Safety-Kleen | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Revenues									795,077
Safety-Kleen | Kleen Performance Products
Disaggregation of Revenue [Line Items]
Revenues									500,278
Corporate Items
Disaggregation of Revenue [Line Items]
Revenues									1,105	$ 2,575	$ 3,067
Corporate Items | United States
Disaggregation of Revenue [Line Items]
Revenues									1,082
Corporate Items | Canada
Disaggregation of Revenue [Line Items]
Revenues									23
Corporate Items | Technical Services
Disaggregation of Revenue [Line Items]
Revenues									0
Corporate Items | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Revenues									0
Corporate Items | Industrial Services
Disaggregation of Revenue [Line Items]
Revenues									0
Corporate Items | Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Revenues									1,105
Corporate Items | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Revenues									0
Corporate Items | Kleen Performance Products
Disaggregation of Revenue [Line Items]
Revenues									$ 0