SEGMENT REPORTING - Third Party Revenues to Direct Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Total revenues	$ 868,678	$ 849,140	$ 1,649,517	$ 1,598,918
Direct revenues
Segment Reporting Information [Line Items]
Total revenues	868,678	849,140	1,649,517	1,598,918
Environmental Services
Segment Reporting Information [Line Items]
Total revenues	526,294	519,916	999,992	959,604
Environmental Services | Intersegment revenues, net
Segment Reporting Information [Line Items]
Total revenues	36,206	34,291	70,281	66,256
Environmental Services | Corporate Items, net
Segment Reporting Information [Line Items]
Total revenues	576	607	1,825	1,401
Environmental Services | Direct revenues
Segment Reporting Information [Line Items]
Total revenues	563,076	554,814	1,072,098	1,027,261
Safety-Kleen
Segment Reporting Information [Line Items]
Total revenues	342,182	328,715	648,729	638,633
Safety-Kleen | Intersegment revenues, net
Segment Reporting Information [Line Items]
Total revenues	(36,206)	(34,291)	(70,281)	(66,256)
Safety-Kleen | Corporate Items, net
Segment Reporting Information [Line Items]
Total revenues	8	11	13	22
Safety-Kleen | Direct revenues
Segment Reporting Information [Line Items]
Total revenues	305,984	294,435	578,461	572,399
Corporate
Segment Reporting Information [Line Items]
Total revenues	202	509	796	681
Corporate | Corporate Items, net
Segment Reporting Information [Line Items]
Total revenues	(584)	(618)	(1,838)	(1,423)
Corporate | Direct revenues
Segment Reporting Information [Line Items]
Total revenues	$ (382)	$ (109)	$ (1,042)	$ (742)