SEGMENT REPORTING - Reconciliation to Consolidated Statements of Income to Adjusted EBITDA (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ 309,070	$ 187,771	$ 489,329	$ 317,222
Reconciliation to Consolidated Statements of Operations:
Accretion of environmental liabilities	3,197	2,873	6,353	5,826
Stock-based compensation	6,835	3,305	12,547	6,785
Depreciation and amortization	87,868	71,592	172,166	143,755
Income from operations	211,170	110,001	298,263	160,856
Other (income) expense, net	(1,265)	1,480	(1,969)	2,708
Gain on sale of business	(8,864)	0	(8,864)	0
Interest expense, net of interest income	26,256	18,051	51,273	35,969
Income before provision for income taxes	195,043	90,470	257,823	122,179
Operating segments | Environmental Services
Segment Reporting Information [Line Items]
Adjusted EBITDA	269,341	176,041	452,943	316,295
Operating segments | Safety-Kleen Sustainability Solutions
Segment Reporting Information [Line Items]
Adjusted EBITDA	97,010	63,314	148,887	94,946
Corporate
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ (57,281)	$ (51,584)	$ (112,501)	$ (94,019)