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Asset Retirement Obligations - Schedule of Changes in Asset Retirement Obligations (Detail) (USD $)
In Thousands, unless otherwise specified
 9 Months Ended
Sep. 30, 2014
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]  
Balance at December 31, 2013 $ 36,458
Liabilities incurred during period 4,850
Liabilities settled during period (2,062) [1]
Accretion expense during period 1,395 [2]
Balance at September 30, 2014 41,504
Asset Retirement Obligation, Revision of Estimate $ 863
[1] Liabilities settled during period include ARO related to the properties sold in the Sanish Divestiture.
[2] Included in depreciation, depletion and amortization on the Company’s Condensed Consolidated Statement of Operations.