Property, Plant and Equipment - Additional Information (Detail) (USD $)	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Dec. 31, 2010
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Total capitalized exploratory well costs	$ 571,776,000	$ 556,412,000	$ 529,246,000	$ 497,765,000
Exploratory well costs capitalized more than one year	489,300,000
Malaysia
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Exploratory well costs capitalized more than one year	270,500,000
United States
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Exploratory well costs capitalized more than one year	189,500,000
Republic of the Congo
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Exploratory well costs capitalized more than one year	$ 29,300,000