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Other Long-Term Obligations and Commitments - Reconciliation of Liability for Plugging and Abandonment Costs (Detail) (USD $)
In Thousands, unless otherwise specified
3 Months Ended 9 Months Ended
Sep. 30, 2014
Sep. 30, 2014
Commitments and Contingencies Disclosure [Abstract]    
Asset retirement obligation - December 31, 2013   $ 10,537
Liabilities incurred   1,579
Liabilities settled   (642)
Gain on settlement of liabilities (1,787) (1,787)
Accretion expense   275
Revisions in estimated liabilities     
Asset retirement obligation - September 30, 2014 $ 9,962 $ 9,962