Reconciliation of Income Taxes Based on U.S. Statutory Tax Rate to Income Tax Expense (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011		Dec. 31, 2010
Reconciliation of Statutory Federal Tax Rate [Line Items]
Income tax expense based on the U.S. statutory tax rate	$ 568,044	$ 522,425		$ 463,978
Foreign income subject to foreign taxes at a rate different than the U.S. statutory rate	5,542	(1,945)		45,859
State income taxes, net of federal benefit	16,090	19,742		10,066
U.S. tax benefit on certain foreign exploration activities	(108,077)	0		0
Increase in deferred tax asset valuation allowance related to other foreign exploration expenditures	87,558	102,714		47,128
Impairment of Azurite field with no tax benefit	70,000	129,010		0
Malaysian tax benefits on prior year costs in Block P	0	(25,573)		0
Other, net	19,779	16,800		9,541
Total	$ 658,936	$ 763,173	[1]	$ 576,572	[1]

[1] Reclassified to conform to current presentation.