BUSINESS COMBINATIONS - Preliminary fair value estimates of assets acquired and liabilities assumed recognized (Details) $ in Millions				3 Months Ended	12 Months Ended
	Jan. 28, 2020 USD ($)	Aug. 01, 2019 USD ($)	Aug. 01, 2019 CAD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Nov. 01, 2019 USD ($)
Consideration paid and the fair value of assets acquired and liabilities assumed
Goodwill				$ 466,031,000	$ 766,980,000
Goodwill impairment charge				300,300,000
Field and Industrial Services
Consideration paid and the fair value of assets acquired and liabilities assumed
Goodwill				298,723,000	298,579,000
Goodwill impairment charge				16,700,000
Environmental Services
Consideration paid and the fair value of assets acquired and liabilities assumed
Goodwill				474,478,000	475,271,000
Goodwill impairment charge				283,600,000
Impact Environmental Services Inc
Consideration paid and the fair value of assets acquired and liabilities assumed
Goodwill				300,000
Total purchase price	$ 3,300,000
Impact Environmental Services Inc | Field and Industrial Services
Consideration paid and the fair value of assets acquired and liabilities assumed
Identifiable intangible assets	900,000
Goodwill	$ 300,000
NRC
Consideration paid and the fair value of assets acquired and liabilities assumed
Current assets				131,653,000	131,653,000
Property and equipment				197,045,000	197,045,000
Identifiable intangible assets				303,600,000	303,600,000
Other assets				41,687,000	41,687,000
Current liabilities				(84,675,000)	(83,460,000)
Deferred income tax liabilities				(56,402,000)	(56,596,000)
Other liabilities				(57,581,000)	(57,581,000)
Total identifiable net assets				475,327,000	476,348,000
Goodwill				549,506,000	548,485,000	$ 549,500,000
Total purchase price				1,024,833,000	$ 1,024,833,000
Goodwill expected to be deductible for income tax purposes						33,300,000
Adjustments
Current liabilities - adjustments				1,215,000
Deferred income tax liabilities - adjustments				(194,000)
Total identifiable net assets - adjustment				(1,021,000)
Goodwill - adjustment				1,021,000
NRC | Field and Industrial Services
Consideration paid and the fair value of assets acquired and liabilities assumed
Goodwill						240,100,000
Adjustments
Goodwill - adjustment				446,000
NRC | Environmental Services
Consideration paid and the fair value of assets acquired and liabilities assumed
Goodwill						$ 309,400,000
Adjustments
Goodwill - adjustment				$ 575,000
US Ecology Sarnia
Consideration paid and the fair value of assets acquired and liabilities assumed
Identifiable intangible assets		$ 6,200,000
Goodwill		7,700,000
Total purchase price		$ 17,900,000	$ 23.5