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COMMITMENTS AND CONTINGENCIES (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]      
Undelivered feedstock $ 14.2   $ 9.2
Shortfall fee expenses 0.4 $ 0.3  
Expenses for environmental monitoring, compliance, and improvements $ 0.3 $ 0.2