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Derivative Instruments - Schedule of Location and Fair Value of Outstanding Commodity Derivative Instruments (Detail) - USD ($)
$ in Thousands
Jun. 30, 2015
Dec. 31, 2014
Derivatives, Fair Value [Line Items]    
Derivative instruments — current assets $ 108,742 $ 302,159
Derivative instruments — non-current assets 1,077 13,348
Total derivative instruments 109,819  
Crude oil [Member]    
Derivatives, Fair Value [Line Items]    
Derivative instruments — current assets 108,742 302,159
Derivative instruments — non-current assets 1,077 13,348
Total derivative instruments $ 109,819 $ 315,507