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Asset Retirement Obligations - Asset Retirement Obligations (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Asset Retirement Obligation [Abstract]    
Beginning of period $ 287,463 $ 230,077
Liabilities incurred 4,595 8,602
Acquisitions 1,584 11,927
Liability released 0 (8,309)
Liabilities settled (18,828) (4,442)
Disposition of wells (45,845) (13,951)
Accretion expense 19,163 15,226
Change in estimate 16,005 48,333
End of period 264,137 287,463
Less current portion (15,071) (15,067)
Long-term asset retirement obligations $ 249,066 $ 272,396