Suspended Exploratory Well Costs - Suspended Exploratory Well Costs (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 Project	Dec. 31, 2011 Project	Dec. 31, 2010 Project
Exploratory Wells Drilled [Line Items]
Balance at beginning of period	$ 93,388	$ 23,908	$ 19,052
Additions to capitalized exploratory well costs pending the determination of proved reserves	153,250	86,996	28,897
Reclassifications to wells, facilities and equipment based on determination of proved reserves	(184,298)	(17,516)	(24,041)
Divested wells	(4,980)
Capitalized exploratory well costs charged to expense
Balance at end of period	57,360	93,388	23,908
Less exploratory well costs that have been capitalized for a period of one year or less	(45,965)	(83,860)	(13,181)
Capitalized exploratory well costs that have been capitalized for a period greater than one year	$ 11,395	$ 9,528	$ 10,727
Number of projects that have exploratory well costs that have been capitalized for a period greater than one year	5	3	4