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Derivatives (Effects Of Derivatives On Measures Of Financial Performance) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Derivative Instruments, Gain (Loss) [Line Items]      
Change in fair value of coal derivatives and coal trading activities, net $ 2,392 $ (5,219) $ 18,601
Designated as Hedging Instrument | Coal Contract      
Derivative Instruments, Gain (Loss) [Line Items]      
Gain (Loss) Recognized in Other Comprehensive Income   4 9,018
Gains (Losses) Reclassified from Other Comprehensive Income into Income   (392) 9,481
Designated as Hedging Instrument | Coal sales | Coal Contract | Revenues      
Derivative Instruments, Gain (Loss) [Line Items]      
Gain (Loss) Recognized in Other Comprehensive Income   500 10,249
Gains (Losses) Reclassified from Other Comprehensive Income into Income   (1,850) 10,167
Designated as Hedging Instrument | Coal purchases | Coal Contract | Cost of sales      
Derivative Instruments, Gain (Loss) [Line Items]      
Gain (Loss) Recognized in Other Comprehensive Income   (496) (1,231)
Gains (Losses) Reclassified from Other Comprehensive Income into Income   1,458 (686)
Not Designated as Hedging Instrument | Coal Contract | Change in fair value of coal derivatives and coal trading activities, net      
Derivative Instruments, Gain (Loss) [Line Items]      
Realized and Unrealized Gain (Loss) on Derivatives   222 (1,013)
Unrealized Gain (Loss) on Derivatives 2,392 (5,517) 19,713
Not Designated as Hedging Instrument | Coal Contract | Other operating (income) expense, net      
Derivative Instruments, Gain (Loss) [Line Items]      
Realized Gain (Loss) on Derivatives $ (27,464) 9,258 487
Not Designated as Hedging Instrument | Natural gas | Change in fair value of coal derivatives and coal trading activities, net      
Derivative Instruments, Gain (Loss) [Line Items]      
Realized and Unrealized Gain (Loss) on Derivatives   76 (99)
Not Designated as Hedging Instrument | Heating oil - diesel purchases | Other operating (income) expense, net      
Derivative Instruments, Gain (Loss) [Line Items]      
Heating oil realized and unrealized gains and losses   $ (558) $ (2,291)