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Asset Retirement Obligations - Asset Retirement Obligations (Detail) - USD ($)
$ in Thousands
6 Months Ended
Jun. 30, 2015
Dec. 31, 2014
Asset Retirement Obligation [Abstract]    
Beginning of period $ 287,463  
Liabilities incurred 2,994  
Liabilities settled (7,410)  
Disposition of wells (4,115)  
Accretion expense 9,570  
Change in estimate 15,690  
End of period 304,192  
Less current portion 17,689 $ 15,067
Long-term asset retirement obligations $ 286,503