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Fair Value - Schedule of Quantitative Information (Details) - Natural Gas Exchange Agreements [Member]
$ in Thousands
3 Months Ended
Mar. 31, 2021
USD ($)
MMBTU
$ / MMBTU
Dec. 31, 2020
USD ($)
Purchase [Member] | Minimum [Member] | Internally Derived Weighted Average Cost Of Gas [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]    
Derivative, Forward Price 1.84  
Transaction/Delivery Volumes | MMBTU 130,000  
Purchase [Member] | Maximum [Member] | Internally Derived Weighted Average Cost Of Gas [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]    
Derivative, Forward Price 2.85  
Transaction/Delivery Volumes | MMBTU 310,000  
Purchase [Member] | Weighted Average [Member] | Internally Derived Weighted Average Cost Of Gas [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]    
Derivative, Forward Price 2.21  
Sales [Member] | Minimum [Member] | Internally Derived Weighted Average Cost Of Gas [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]    
Derivative, Forward Price 1.90  
Transaction/Delivery Volumes | MMBTU 75,000  
Sales [Member] | Maximum [Member] | Internally Derived Weighted Average Cost Of Gas [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]    
Derivative, Forward Price 4.25  
Transaction/Delivery Volumes | MMBTU 310,000  
Sales [Member] | Weighted Average [Member] | Internally Derived Weighted Average Cost Of Gas [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]    
Derivative, Forward Price 3.53  
Fair Value, Recurring [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]    
Derivative Liability | $ $ (6,201) $ (8,410)