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Derivatives (Net Derivatives As Reflected On The Balance Sheets) (Details) - USD ($)
$ in Thousands
Mar. 31, 2016
Dec. 31, 2015
Derivatives, Fair Value [Line Items]    
Net derivatives as classified in the balance sheet $ 7,189 $ 9,052
Heating Oil [Member] | Other Current Assets [Member]    
Derivatives, Fair Value [Line Items]    
Net derivatives as classified in the balance sheet 1,381 1,017
Coal Contract [Member] | Coal Derivative Assets [Member]    
Derivatives, Fair Value [Line Items]    
Net derivatives as classified in the balance sheet 5,808 8,035
Coal Contract [Member] | Accrued expenses and other current liabilities [Member]    
Derivatives, Fair Value [Line Items]    
Net derivatives as classified in the balance sheet $ 0 $ 0