GOODWILL AND INTANGIBLE ASSETS - Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Oct. 31, 2020	Jan. 28, 2020	Nov. 01, 2019	Aug. 01, 2019
Intangible Assets
Amortizing intangible assets, Cost	$ 545,634	$ 545,499
Accumulated amortization	(138,929)	(104,376)
Amortizing intangible assets, Net	406,705	441,123
Total intangible assets, cost	628,502	628,364
Total intangible assets, net	489,573	523,988
Goodwill	413,126	413,037	$ 766,980
Amortization of intangible assets	34,614	37,344	15,491
Permits and license
Intangible Assets
Non-amortizing intangible assets	82,734	82,732
Tradename
Intangible Assets
Non-amortizing intangible assets	134	133
Permits, licenses and lease
Intangible Assets
Amortizing intangible assets, Cost	174,959	174,885
Accumulated amortization	(27,170)	(23,005)
Amortizing intangible assets, Net	147,789	151,880
Customer relationships
Intangible Assets
Amortizing intangible assets, Cost	340,065	340,032
Accumulated amortization	(87,952)	(61,778)
Amortizing intangible assets, Net	252,113	278,254
Technology - Formulae and processes
Intangible Assets
Amortizing intangible assets, Cost	7,166	7,142
Accumulated amortization	(2,531)	(2,293)
Amortizing intangible assets, Net	4,635	4,849
Customer backlog
Intangible Assets
Amortizing intangible assets, Cost	3,652	3,652
Accumulated amortization	(2,752)	(2,387)
Amortizing intangible assets, Net	900	1,265
Tradename
Intangible Assets
Amortizing intangible assets, Cost	10,390	10,390
Accumulated amortization	(10,390)	(8,015)
Amortizing intangible assets, Net		2,375
Developed software
Intangible Assets
Amortizing intangible assets, Cost	2,903	2,902
Accumulated amortization	(2,475)	(2,182)
Amortizing intangible assets, Net	428	720
Non-compete agreements
Intangible Assets
Amortizing intangible assets, Cost	5,573	5,571
Accumulated amortization	(5,211)	(4,318)
Amortizing intangible assets, Net	362	1,253
Internet domain and website
Intangible Assets
Amortizing intangible assets, Cost	536	536
Accumulated amortization	(213)	(184)
Amortizing intangible assets, Net	323	352
Database
Intangible Assets
Amortizing intangible assets, Cost	390	389
Accumulated amortization	(235)	(214)
Amortizing intangible assets, Net	155	175
Impact Environmental Services Inc
Intangible Assets
Amortizing intangible assets, Cost					$ 900
Goodwill					$ 300
ES&H Dallas
Intangible Assets
Goodwill							$ 7,700
US Ecology Sarnia
Intangible Assets
Goodwill							$ 7,700
NRC
Intangible Assets
Goodwill	577,400			$ 577,398		$ 577,400
Field & Industrial Services
Intangible Assets
Goodwill	$ 237,368	$ 237,341	$ 298,579
Field & Industrial Services | NRC
Intangible Assets
Goodwill						$ 177,900