REVENUES - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue [Line Items]
Total third party revenues	$ 858,563	$ 780,839
Technical Services
Disaggregation of Revenue [Line Items]
Total third party revenues	275,273	251,919
Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total third party revenues	105,912	71,626
Industrial Services and Other
Disaggregation of Revenue [Line Items]
Total third party revenues	147,009	150,747
Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total third party revenues	214,481	207,083
Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total third party revenues	115,888	99,464
United States
Disaggregation of Revenue [Line Items]
Total third party revenues	746,245	675,337
Canada
Disaggregation of Revenue [Line Items]
Total third party revenues	112,318	105,502
Environmental Services
Disaggregation of Revenue [Line Items]
Total third party revenues	566,362	509,022
Safety-Kleen
Disaggregation of Revenue [Line Items]
Total third party revenues	293,212	272,477
Operating segments | Environmental Services
Disaggregation of Revenue [Line Items]
Total third party revenues	528,104	473,698
Operating segments | Environmental Services | Technical Services
Disaggregation of Revenue [Line Items]
Total third party revenues	275,273	251,919
Operating segments | Environmental Services | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total third party revenues	105,912	71,626
Operating segments | Environmental Services | Industrial Services and Other
Disaggregation of Revenue [Line Items]
Total third party revenues	146,919	150,153
Operating segments | Environmental Services | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0
Operating segments | Environmental Services | Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0
Operating segments | Environmental Services | Oil, Gas and Lodging Services
Disaggregation of Revenue [Line Items]
Total third party revenues		34,055
Operating segments | Environmental Services | United States
Disaggregation of Revenue [Line Items]
Total third party revenues	440,014	388,169
Operating segments | Environmental Services | Canada
Disaggregation of Revenue [Line Items]
Total third party revenues	88,090	85,529
Operating segments | Safety-Kleen
Disaggregation of Revenue [Line Items]
Total third party revenues	330,369	306,547
Operating segments | Safety-Kleen | Technical Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0
Operating segments | Safety-Kleen | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0
Operating segments | Safety-Kleen | Industrial Services and Other
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0
Operating segments | Safety-Kleen | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total third party revenues	214,481	207,083
Operating segments | Safety-Kleen | Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total third party revenues	115,888	99,464
Operating segments | Safety-Kleen | United States
Disaggregation of Revenue [Line Items]
Total third party revenues	306,533	286,574
Operating segments | Safety-Kleen | Canada
Disaggregation of Revenue [Line Items]
Total third party revenues	23,836	19,973
Corporate Items
Disaggregation of Revenue [Line Items]
Total third party revenues	90	594
Corporate Items | Technical Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0
Corporate Items | Field and Emergency Response Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0
Corporate Items | Industrial Services and Other
Disaggregation of Revenue [Line Items]
Total third party revenues	90	594
Corporate Items | Safety-Kleen Environmental Services
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0
Corporate Items | Safety-Kleen Oil
Disaggregation of Revenue [Line Items]
Total third party revenues	0	0
Corporate Items | Oil, Gas and Lodging Services
Disaggregation of Revenue [Line Items]
Total third party revenues		594
Corporate Items | United States
Disaggregation of Revenue [Line Items]
Total third party revenues	(302)	594
Corporate Items | Canada
Disaggregation of Revenue [Line Items]
Total third party revenues	$ 392	$ 0