SEGMENT REPORTING - Third Party Revenues to Direct Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting Information [Line Items]
Total revenues	$ 710,000	$ 868,678	$ 1,568,563	$ 1,649,517
Corporate
Segment Reporting Information [Line Items]
Total revenues	56	202	146	796
Corporate Items, net
Segment Reporting Information [Line Items]
Total revenues	(1,526)	(584)	(2,627)	(1,838)
Operating and Corporate non-segment
Segment Reporting Information [Line Items]
Total revenues	(1,470)	(382)	(2,481)	(1,042)
Environmental Services
Segment Reporting Information [Line Items]
Total revenues	496,914	563,076	1,063,276	1,072,098
Environmental Services | Operating segments
Segment Reporting Information [Line Items]
Total revenues	464,354	526,294	992,458	999,992
Environmental Services | Intersegment revenues, net
Segment Reporting Information [Line Items]
Total revenues	31,171	36,206	68,334	70,281
Environmental Services | Corporate Items, net
Segment Reporting Information [Line Items]
Total revenues	1,389	576	2,484	1,825
Safety-Kleen
Segment Reporting Information [Line Items]
Total revenues	214,556	305,984	507,768	578,461
Safety-Kleen | Operating segments
Segment Reporting Information [Line Items]
Total revenues	245,590	342,182	575,959	648,729
Safety-Kleen | Intersegment revenues, net
Segment Reporting Information [Line Items]
Total revenues	(31,171)	(36,206)	(68,334)	(70,281)
Safety-Kleen | Corporate Items, net
Segment Reporting Information [Line Items]
Total revenues	$ 137	$ 8	$ 143	$ 13