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Supplemental Information on Oil and Natural Gas Operations - Unaudited - Financial Data Related to Oil and Gas Producing Activities (Parenthetical) (Detail) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Extractive Industries [Abstract]      
Asset retirement costs included in development cost $ (20,305)us-gaap_CapitalizedCostsAssetRetirementCosts $ 54,737us-gaap_CapitalizedCostsAssetRetirementCosts $ 95,293us-gaap_CapitalizedCostsAssetRetirementCosts