REVENUES (Disaggregation of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Revenues	$ 749,778	$ 688,941
United States
Disaggregation of Revenue [Line Items]
Revenues	631,759	585,987
Canada
Disaggregation of Revenue [Line Items]
Revenues	118,019	102,954
Technical Services
Disaggregation of Revenue [Line Items]
Revenues	236,306	230,218
Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Revenues	69,935	61,019
Industrial Services
Disaggregation of Revenue [Line Items]
Revenues	103,763	75,068
Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Revenues	29,856	29,735
Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Revenues	194,161	191,727
Kleen Performance Products
Disaggregation of Revenue [Line Items]
Revenues	115,757	101,174
Environmental Services
Disaggregation of Revenue [Line Items]
Revenues	439,688	395,907
Environmental Services | United States
Disaggregation of Revenue [Line Items]
Revenues	343,972	313,783
Environmental Services | Canada
Disaggregation of Revenue [Line Items]
Revenues	95,716	82,124
Environmental Services | Technical Services
Disaggregation of Revenue [Line Items]
Revenues	236,306	230,218
Environmental Services | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Revenues	69,935	61,019
Environmental Services | Industrial Services
Disaggregation of Revenue [Line Items]
Revenues	103,763	75,068
Environmental Services | Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Revenues	29,684	29,602
Environmental Services | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Revenues	0	0
Environmental Services | Kleen Performance Products
Disaggregation of Revenue [Line Items]
Revenues	0	0
Safety-Kleen
Disaggregation of Revenue [Line Items]
Revenues	309,918	292,901
Safety-Kleen | United States
Disaggregation of Revenue [Line Items]
Revenues	287,642	272,071
Safety-Kleen | Canada
Disaggregation of Revenue [Line Items]
Revenues	22,276	20,830
Safety-Kleen | Technical Services
Disaggregation of Revenue [Line Items]
Revenues	0	0
Safety-Kleen | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Revenues	0	0
Safety-Kleen | Industrial Services
Disaggregation of Revenue [Line Items]
Revenues	0	0
Safety-Kleen | Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Revenues	0	0
Safety-Kleen | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Revenues	194,161	191,727
Safety-Kleen | Kleen Performance Products
Disaggregation of Revenue [Line Items]
Revenues	115,757	101,174
Corporate Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	172	133
Corporate Segment [Member] | United States
Disaggregation of Revenue [Line Items]
Revenues	145	133
Corporate Segment [Member] | Canada
Disaggregation of Revenue [Line Items]
Revenues	27	0
Corporate Segment [Member] | Technical Services
Disaggregation of Revenue [Line Items]
Revenues	0	0
Corporate Segment [Member] | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Revenues	0	0
Corporate Segment [Member] | Industrial Services
Disaggregation of Revenue [Line Items]
Revenues	0	0
Corporate Segment [Member] | Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Revenues	172	133
Corporate Segment [Member] | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Revenues	0	0
Corporate Segment [Member] | Kleen Performance Products
Disaggregation of Revenue [Line Items]
Revenues	$ 0	$ 0