Quarterly report pursuant to Section 13 or 15(d)

Derivative Financial Instruments - Changes in Fair Value of Commodity Derivative Contracts (Details)

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Derivative Financial Instruments - Changes in Fair Value of Commodity Derivative Contracts (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Gain Loss On Derivative Instruments Net Pretax [Abstract]    
Derivative loss $ 0 $ 7,492