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Asset Retirement Obligations - Asset Retirement Obligations (Detail) - USD ($)
$ in Thousands
9 Months Ended
Sep. 30, 2015
Dec. 31, 2014
Asset Retirement Obligation [Abstract]    
Beginning of period $ 287,463  
Liabilities incurred 4,135  
Liabilities settled (13,205)  
Disposition of wells (4,116)  
Accretion expense 14,521  
Change in estimate 15,727  
End of period 304,525  
Less current portion (17,689) $ (15,067)
Long-term asset retirement obligations $ 286,836