GOODWILL AND OTHER INTANGIBLE ASSETS - Changes to Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Goodwill [Roll Forward]
Goodwill, beginning of period	$ 527,023	$ 525,013
Increase from current period acquisition	699,812	1,439
Measurement period adjustments from prior period acquisitions		23
Decrease from disposition of business		(674)
Foreign currency translation	207	1,222
Goodwill, end of period	1,227,042	527,023
Environmental Services
Goodwill [Roll Forward]
Goodwill, beginning of period		401,680
Increase from current period acquisition	683,463	0
Measurement period adjustments from prior period acquisitions		23
Decrease from disposition of business		(674)
Foreign currency translation	153	889
Goodwill, end of period	1,085,534
Safety-Kleen Sustainability Solutions
Goodwill [Roll Forward]
Goodwill, beginning of period		123,333
Increase from current period acquisition	16,349	1,439
Measurement period adjustments from prior period acquisitions		0
Decrease from disposition of business		0
Foreign currency translation	54	$ 333
Goodwill, end of period	$ 141,508