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Supplemental Oil and Gas Disclosures - Additional Information (Detail) (USD $) In Millions, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013
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Oil and Gas Exploration and Production Industries Disclosures [Abstract] |  |
Asset retirement costs | $ 36.9 us-gaap_CapitalizedCostsAssetRetirementCosts | $ 32.6 us-gaap_CapitalizedCostsAssetRetirementCosts

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- Definition The amount of asset retirement costs previously incurred and capitalized separately from the capitalized amount of the associated long-lived assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e61901-109447 + Details
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