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COMMITMENTS AND CONTINGENCIES (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2021
Jun. 30, 2020
Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]          
Undelivered feedstock $ 17.0   $ 17.0   $ 9.2
Shortfall fee expenses 0.4 $ 0.6 0.4 $ 1.0  
Expenses for environmental monitoring, compliance, and improvements $ 0.3 $ 0.3 $ 0.6 $ 0.5