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Derivative Instruments (Details)
$ in Thousands
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2021
USD ($)
Sep. 30, 2021
USD ($)
BTU
Sep. 30, 2020
USD ($)
Dec. 31, 2020
USD ($)
BTU
Derivative [Line Items]        
Gain (loss) on derivatives $ (5,800) $ (8,661) $ 0  
Natural Gas | Commodity Contract | Not Designated as Hedging Instrument        
Derivative [Line Items]        
Derivative energy measure (in BTUs) | BTU   2,500   0
Natural gas swap contracts, current asset       $ 0
Natural gas swap contracts, current liability $ 5,800 $ 5,800   $ 0