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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
Mar. 31, 2015
Commitments and Contingencies Disclosure [Abstract]  
Asset retirement obligation at beginning of period $ 12,501us-gaap_AssetRetirementObligation
Liabilities incurred 60us-gaap_AssetRetirementObligationLiabilitiesIncurred
Liabilities settled (477)us-gaap_AssetRetirementObligationLiabilitiesSettled
Accretion expense 133us-gaap_AssetRetirementObligationAccretionExpense
Asset retirement obligation at end of period $ 12,217us-gaap_AssetRetirementObligation