Net Changes in Capitalized Exploratory Well Costs (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
Sep. 30, 2012	Sep. 30, 2011
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Beginning balance	$ 556,412	$ 497,765
Additions pending the determination of proved reserves	143,863	31,481
Reclassifications to proved properties based on the determination of proved reserves	(76,633)	0
Capitalized exploratory well costs charged to expense	(51,866)	0
Ending balance	$ 571,776	$ 529,246

Previously capitalized costs of the drilling of wells that were reclassified as part of the costs of the enterprise's wells and related equipment and facilities at the time that proved reserves were found.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS19-1

-Paragraph 10

-Subparagraph a

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

-Paragraph 1B

-Subparagraph (a)(2)

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