REVENUES (Disaggregation of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Total third party revenues	$ 780,839	$ 749,778
United States
Disaggregation of Revenue [Line Items]
Total third party revenues	675,337	631,759
Canada
Disaggregation of Revenue [Line Items]
Total third party revenues	105,502	118,019
Technical Services
Disaggregation of Revenue [Line Items]
Total third party revenues	251,919	236,306
Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total third party revenues	71,626	69,935
Industrial Services
Disaggregation of Revenue [Line Items]
Total third party revenues	116,098	103,763
Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Total third party revenues	34,649	29,856
Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total third party revenues	207,083	194,161
Safety-Kleen Oil (2)
Disaggregation of Revenue [Line Items]
Total third party revenues	99,464	115,757
Environmental Services
Disaggregation of Revenue [Line Items]
Total third party revenues	473,698	439,688
Environmental Services | United States
Disaggregation of Revenue [Line Items]
Total third party revenues	388,169	343,972
Environmental Services | Canada
Disaggregation of Revenue [Line Items]
Total third party revenues	85,529	95,716
Environmental Services | Technical Services
Disaggregation of Revenue [Line Items]
Total third party revenues	251,919	236,306
Environmental Services | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total third party revenues	71,626	69,935
Environmental Services | Industrial Services
Disaggregation of Revenue [Line Items]
Total third party revenues	116,098	103,763
Environmental Services | Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Total third party revenues	34,055	29,684
Environmental Services | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0
Environmental Services | Safety-Kleen Oil (2)
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0
Safety-Kleen
Disaggregation of Revenue [Line Items]
Total third party revenues	306,547	309,918
Safety-Kleen | United States
Disaggregation of Revenue [Line Items]
Total third party revenues	286,574	287,642
Safety-Kleen | Canada
Disaggregation of Revenue [Line Items]
Total third party revenues	19,973	22,276
Safety-Kleen | Technical Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0
Safety-Kleen | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0
Safety-Kleen | Industrial Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0
Safety-Kleen | Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0
Safety-Kleen | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total third party revenues	207,083	194,161
Safety-Kleen | Safety-Kleen Oil (2)
Disaggregation of Revenue [Line Items]
Total third party revenues	99,464	115,757
Corporate
Disaggregation of Revenue [Line Items]
Total third party revenues	594	172
Corporate | United States
Disaggregation of Revenue [Line Items]
Total third party revenues	594	145
Corporate | Canada
Disaggregation of Revenue [Line Items]
Total third party revenues	0	27
Corporate | Technical Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0
Corporate | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0
Corporate | Industrial Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0
Corporate | Oil, Gas and Lodging Services and Other
Disaggregation of Revenue [Line Items]
Total third party revenues	594	172
Corporate | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0
Corporate | Safety-Kleen Oil (2)
Disaggregation of Revenue [Line Items]
Total third party revenues	$ 0	$ 0