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Derivatives (Effects Of Derivatives On Measures Of Financial Performance) (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Successor [Member] | Designated as Hedging Instrument [Member]    
Derivative Instruments, Gain (Loss) [Line Items]    
Gain (Loss) Recognized in Other Comprehensive Income(Effective Portion) $ 19  
Gains (Losses) Reclassified from Other Comprehensive Income into Income (Effective Portion) 0  
Successor [Member] | Designated as Hedging Instrument [Member] | Coal sales [Member] | Coal Contract [Member] | Sales Revenue, Net [Member]    
Derivative Instruments, Gain (Loss) [Line Items]    
Gain (Loss) Recognized in Other Comprehensive Income(Effective Portion) 220  
Gains (Losses) Reclassified from Other Comprehensive Income into Income (Effective Portion) 0  
Successor [Member] | Designated as Hedging Instrument [Member] | Coal purchases [Member] | Coal Contract [Member] | Cost of Sales [Member]    
Derivative Instruments, Gain (Loss) [Line Items]    
Gain (Loss) Recognized in Other Comprehensive Income(Effective Portion) (201)  
Gains (Losses) Reclassified from Other Comprehensive Income into Income (Effective Portion) 0  
Successor [Member] | 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 26  
Successor [Member] | 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 0  
Successor [Member] | 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 (469)  
Successor [Member] | 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 (3,578)  
Successor [Member] | Not Designated as Hedging Instrument [Member] | Foreign Currency [Member] | Other Operating Income (Expense) [Member]    
Derivative Instruments, Gain (Loss) [Line Items]    
Heating oil realized and unrealized gains and losses $ 0  
Predecessor [Member] | Designated as Hedging Instrument [Member]    
Derivative Instruments, Gain (Loss) [Line Items]    
Gain (Loss) Recognized in Other Comprehensive Income(Effective Portion)   $ 2
Gains (Losses) Reclassified from Other Comprehensive Income into Income (Effective Portion)   226
Predecessor [Member] | Designated as Hedging Instrument [Member] | Coal sales [Member] | Coal Contract [Member] | Sales Revenue, Net [Member]    
Derivative Instruments, Gain (Loss) [Line Items]    
Gain (Loss) Recognized in Other Comprehensive Income(Effective Portion)   13
Gains (Losses) Reclassified from Other Comprehensive Income into Income (Effective Portion)   1,369
Predecessor [Member] | Designated as Hedging Instrument [Member] | Coal purchases [Member] | Coal Contract [Member] | Cost of Sales [Member]    
Derivative Instruments, Gain (Loss) [Line Items]    
Gain (Loss) Recognized in Other Comprehensive Income(Effective Portion)   (11)
Gains (Losses) Reclassified from Other Comprehensive Income into Income (Effective Portion)   (1,143)
Predecessor [Member] | 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   (1,115)
Predecessor [Member] | 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   163
Predecessor [Member] | 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   (469)
Predecessor [Member] | 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   (443)
Predecessor [Member] | Not Designated as Hedging Instrument [Member] | Foreign Currency [Member] | Other Operating Income (Expense) [Member]    
Derivative Instruments, Gain (Loss) [Line Items]    
Heating oil realized and unrealized gains and losses   $ (171)