Property, Plant and Equipment - Additional Information (Detail) (USD $)	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2011
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Total capitalized exploratory well costs	$ 444,428,000	$ 445,697,000	$ 567,645,000	$ 556,412,000
Exploratory well costs capitalized more than one year	394,400,000
Malaysia
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Exploratory well costs capitalized more than one year	273,000,000
United States
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Exploratory well costs capitalized more than one year	114,800,000
Brunei
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Exploratory well costs capitalized more than one year	$ 6,600,000