SEGMENT REPORTING - Third Party Revenues to Direct Revenues (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Total revenues	$ 858,563	$ 780,839
Corporate Items
Segment Reporting Information [Line Items]
Total revenues	90	594
Corporate Items, net
Segment Reporting Information [Line Items]
Total revenues	(1,101)	(1,254)
Operating and Corporate non-segment
Segment Reporting Information [Line Items]
Total revenues	(1,011)	(660)
Environmental Services
Segment Reporting Information [Line Items]
Total revenues	566,362	509,022
Environmental Services | Operating segments
Segment Reporting Information [Line Items]
Total revenues	528,104	473,698
Environmental Services | Intersegment revenues, net
Segment Reporting Information [Line Items]
Total revenues	37,163	34,075
Environmental Services | Corporate Items, net
Segment Reporting Information [Line Items]
Total revenues	1,095	1,249
Safety-Kleen
Segment Reporting Information [Line Items]
Total revenues	293,212	272,477
Safety-Kleen | Operating segments
Segment Reporting Information [Line Items]
Total revenues	330,369	306,547
Safety-Kleen | Intersegment revenues, net
Segment Reporting Information [Line Items]
Total revenues	(37,163)	(34,075)
Safety-Kleen | Corporate Items, net
Segment Reporting Information [Line Items]
Total revenues	$ 6	$ 5