Net Changes in Capitalized Exploratory Well Costs (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Beginning balance	$ 556,412	$ 497,765	$ 369,862
Additions to capitalized exploratory well costs pending the determination of proved reserves	135,849	86,035	137,403
Reclassifications to proved properties based on the determination of proved reserves	(165,377)	0	0
Capitalized exploratory well costs charged to expense or sold	(81,187)	(27,388)	(9,500)
Ending Balance	$ 445,697	$ 556,412	$ 497,765

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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)

-URI http://asc.fasb.org/extlink&oid=8451039&loc=SL6806780-109447

Name:	us-gaap_ReclassificationToWellFacilitiesAndEquipmentBasedOnDeterminationOfProvedReserves
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration