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Asset Retirement Obligations - Asset Retirement Obligations (Detail) (USD $)
In Thousands, unless otherwise specified
6 Months Ended
Jun. 30, 2014
Dec. 31, 2013
Asset Retirement Obligation [Abstract]    
Beginning of period $ 230,077  
Liabilities incurred 3,854  
Acquisitions 11,927  
Disposition of wells (12,057)  
Liabilities settled (2,142)  
Change in estimate 1,777  
Accretion expense 7,370  
End of period 240,806  
Less current portion (5,037) (5,037)
Long-term asset retirement obligations $ 235,769