Quarterly report pursuant to Section 13 or 15(d)

Derivative Financial Instruments - Estimated Fair Value of Derivative Contracts (Details)

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Derivative Financial Instruments - Estimated Fair Value of Derivative Contracts (Details)
$ in Thousands
Sep. 30, 2015
USD ($)
Prepaid And Other Assets (Current)  
Derivatives Fair Value [Line Items]  
Fair value of commodity derivative contracts $ 5,970
Other Assets (Noncurrent)  
Derivatives Fair Value [Line Items]  
Fair value of commodity derivative contracts $ 1,044