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Derivatives (Effects Of Derivatives On Measures Of Financial Performance) (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2015
Jun. 30, 2014
Jun. 30, 2015
Jun. 30, 2014
Designated as Hedging Instrument [Member]        
Derivative Instruments, Gain (Loss) [Line Items]        
Gain (Loss) Recognized in Other Comprehensive Income(Effective Portion) $ (476) $ 1,158 $ 5,051 $ 1,232
Gains (Losses) Reclassified from Other Comprehensive Income into Income (Effective Portion) 2,727 151 3,208 454
Designated as Hedging Instrument [Member] | Coal Contract [Member] | Coal sales [Member]        
Derivative Instruments, Gain (Loss) [Line Items]        
Gain (Loss) Recognized in Other Comprehensive Income(Effective Portion) (1,163) 1,870 9,102 1,355
Designated as Hedging Instrument [Member] | Coal Contract [Member] | Coal sales [Member] | Sales Revenue, Net [Member]        
Derivative Instruments, Gain (Loss) [Line Items]        
Gains (Losses) Reclassified from Other Comprehensive Income into Income (Effective Portion) 4,990 223 5,872 930
Designated as Hedging Instrument [Member] | Coal Contract [Member] | Coal purchases [Member]        
Derivative Instruments, Gain (Loss) [Line Items]        
Gain (Loss) Recognized in Other Comprehensive Income(Effective Portion) 687 (712) (4,051) (123)
Designated as Hedging Instrument [Member] | Coal Contract [Member] | Coal purchases [Member] | Cost of Sales [Member]        
Derivative Instruments, Gain (Loss) [Line Items]        
Gains (Losses) Reclassified from Other Comprehensive Income into Income (Effective Portion) (2,263) (72) (2,664) (476)
Not Designated as Hedging Instrument [Member] | Coal Contract [Member] | Change in Fair Value of Coal Derivatives and Coal Trading Activity, Net [Member]        
Derivative Instruments, Gain (Loss) [Line Items]        
Unrealized Gain (Loss) on Derivatives (875) 147 (1,286) (1,155)
Not Designated as Hedging Instrument [Member] | Coal Contract [Member] | Other Operating Income (Expense) [Member]        
Derivative Instruments, Gain (Loss) [Line Items]        
Realized Gain (Loss) on Derivatives 826 1,318 1,917 4,197
Not Designated as Hedging Instrument [Member] | Natural Gas [Member] | Change in Fair Value of Coal Derivatives and Coal Trading Activity, Net [Member]        
Derivative Instruments, Gain (Loss) [Line Items]        
Unrealized Gain (Loss) on Derivatives (221) (267) (62) (259)
Not Designated as Hedging Instrument [Member] | Heating Oil-Diesel Purchases [Member] | Other Operating Income (Expense) [Member]        
Derivative Instruments, Gain (Loss) [Line Items]        
Heating oil realized and unrealized gains and losses 628 0 (1,737) (2,963)
Not Designated as Hedging Instrument [Member] | Heating Oil-Fuel Surcharges [Member] | Other Operating Income (Expense) [Member]        
Derivative Instruments, Gain (Loss) [Line Items]        
Heating oil realized and unrealized gains and losses $ 0 $ (47) $ 0 $ (301)