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Derivatives (Disclosure Of Fair Value Of Derivatives) (Details) - USD ($)
$ in Thousands
Mar. 31, 2021
Dec. 31, 2020
Derivative [Line Items]    
Derivative Assets $ 2,890 $ 3,245
Derivative Liabilities (2,889) (2,399)
Effect of counterparty netting in derivative assets (2,419) (2,392)
Effect of counterparty netting in derivative liabilities 2,419 2,392
Derivative Asset 471 853
Derivative Liability (470) (7)
Net derivatives as classified in the balance sheets 1 846
Accrued expenses and other current liabilities    
Derivative [Line Items]    
Net derivatives as classified in the balance sheets (470) (7)
Not Designated as Hedging Instrument    
Derivative [Line Items]    
Derivative Assets 2,890 3,245
Derivative Liabilities (2,889) (2,399)
Not Designated as Hedging Instrument | Coal Contract    
Derivative [Line Items]    
Derivative Assets 1,892 1,914
Derivative Liabilities (1,653) (1,595)
Coal Contract | Designated as Hedging Instrument    
Derivative [Line Items]    
Derivative Liabilities   0
Coal Contract | Not Designated as Hedging Instrument    
Derivative [Line Items]    
Derivative Assets 998 1,094
Derivative Liabilities $ (1,236) (804)
Heating oil - diesel purchases | Not Designated as Hedging Instrument    
Derivative [Line Items]    
Derivative Assets   237
Derivative Liabilities   $ 0