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Summary of Significant Accounting Policies - Summary of Changes in Reserve for Future Abandonment Costs (Detail) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Asset Retirement Obligations Noncurrent [Abstract]    
Reserve for Future Abandonment Costs at beginning of the year $ 14,534us-gaap_AssetRetirementObligationsNoncurrent $ 16,387us-gaap_AssetRetirementObligationsNoncurrent
New wells placed on production 1,480us-gaap_AssetRetirementObligationLiabilitiesIncurred 1,083us-gaap_AssetRetirementObligationLiabilitiesIncurred
Changes in estimates (1,796)us-gaap_AssetRetirementObligationRevisionOfEstimate (3,324)us-gaap_AssetRetirementObligationRevisionOfEstimate
Liabilities settled and assets disposed of (153)us-gaap_AssetRetirementObligationLiabilitiesSettled (558)us-gaap_AssetRetirementObligationLiabilitiesSettled
Accretion expense 835us-gaap_AssetRetirementObligationAccretionExpense 946us-gaap_AssetRetirementObligationAccretionExpense
Reserve for Future Abandonment Costs at end of the year $ 14,900us-gaap_AssetRetirementObligationsNoncurrent $ 14,534us-gaap_AssetRetirementObligationsNoncurrent