Annual report pursuant to Section 13 and 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
Dec. 31, 2015
USD ($)
Prepaid And Other Assets - Current  
Derivatives Fair Value [Line Items]  
Fair value of commodity derivative contracts $ 7,672