BUSINESS COMBINATIONS - Merger consideration (Details)		9 Months Ended
	Nov. 01, 2019 USD ($) Y $ / shares shares	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Oct. 31, 2019 $ / shares
Business Acquisition [Line Items]
Proceeds from term loan		$ 90,000,000	$ 20,000,000
NRC
Business Acquisition [Line Items]
Repayment of NRC's term loan and revolving credit facility	$ 398,373,000
Total merger consideration	1,024,833,000
Transaction fees and expenses	398,400,000
Proceeds from term loan	$ 450,000,000.0
Term of long term debt	7 years
NRC | Common Stock
Business Acquisition [Line Items]
Fair value of US Ecology common stock issued	$ 581,101,000
Shares Issued | shares	9,337,949
Closing share price | $ / shares				$ 62.23
NRC | Warrants
Business Acquisition [Line Items]
Fair value of replacement warrants issued	$ 44,858,000
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	$ 141,000
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	$ 360,000
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	1.5
NRC | Stock options | Expected term
Business Acquisition [Line Items]
Fair value of option | Y	1