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Property, Plant and Equipment (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified | Mar. 31, 2013 | Dec. 31, 2012
--- | --- | ---
Oil and natural gas proved properties |  |
Property, Plant and Equipment [Line Items] |  |
Cumulative capitalized interest | $ 14.7 | $ 11.7
Non-oil and natural gas equipment |  |
Property, Plant and Equipment [Line Items] |  |
Cumulative capitalized interest | $ 12.4 | $ 11.4

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- Definition Amount of accumulated interest costs capitalized as part of property, plant and equipment cost basis. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Details
Name: | us-gaap_PropertyPlantAndEquipmentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration