Derivatives (Schedule of Price Risk Derivatives) (Details)
Mar. 31, 2015
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Coal sales [Member]  
Derivative [Line Items]  
Derivatives Held 3,875,000
Coal purchases [Member]  
Derivative [Line Items]  
Derivatives Held 1,732,000
Year One, Remainder [Member] | Coal sales [Member]  
Derivative [Line Items]  
Derivatives Held 3,595,000
Year One, Remainder [Member] | Coal purchases [Member]  
Derivative [Line Items]  
Derivatives Held 1,672,000
Year Two [Member] | Coal sales [Member]  
Derivative [Line Items]  
Derivatives Held 280,000
Year Two [Member] | Coal purchases [Member]  
Derivative [Line Items]  
Derivatives Held 60,000