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BUSINESS COMBINATIONS - Merger consideration (Details) $ / shares in Units, $ in Thousands		12 Months Ended
	Nov. 01, 2019 USD ($) $ / shares Y shares	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Oct. 31, 2019 $ / shares
Business Acquisition [Line Items]
Proceeds from term loan		$ 90,000	$ 491,875
NRC
Business Acquisition [Line Items]
Fair value of US Ecology common stock issued			$ 626,460
Repayment of NRC's term loan and revolving credit facility	$ 398,373
Total merger consideration	1,024,833
Proceeds from term loan	$ 450,000
Term of long term debt	7 years
NRC \| Common Stock
Business Acquisition [Line Items]
Fair value of US Ecology common stock issued	$ 581,101
Shares Issued \| shares	9,337,949
Closing share price \| $ / shares				$ 62.23
NRC \| Warrants
Business Acquisition [Line Items]
Fair value of replacement warrants issued	$ 44,858
Shares Issued \| shares	3,772,753
Fair value per warrant \| $ / shares	$ 11.89
Closing share price \| $ / shares				$ 2.33
Exchange ratio	0.196
NRC \| RSUs
Business Acquisition [Line Items]
Fair value of replacement RSUs issued	$ 141
Shares Issued \| shares	118,239
Ratio of precombination service period to vesting period	1.90%
NRC \| Stock options
Business Acquisition [Line Items]
Fair value of replacement stock options	$ 360
Shares Issued \| shares	29,400
Fair value per option \| $ / shares	$ 12.26
Strike price \| $ / shares	$ 52.30
NRC \| Stock options \| Dividend yield
Business Acquisition [Line Items]
Fair value of option	1.2
NRC \| Stock options \| Expected volatility
Business Acquisition [Line Items]
Fair value of option	28.9
NRC \| Stock options \| Risk free rate
Business Acquisition [Line Items]
Fair value of option \| $ / shares	1.5
NRC \| Stock options \| Expected term
Business Acquisition [Line Items]
Fair value of option \| Y	1