Income Tax Expense (Benefit) (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Reconciliation of Provision of Income Taxes [Line Items]
Current			$ 155,100,000	$ 23,200,000
Deferred			(43,400,000)	8,100,000
Income taxes	25,480,000	13,783,000	111,720,000	31,337,000
Federal
Reconciliation of Provision of Income Taxes [Line Items]
Current			154,300,000	21,800,000
Deferred			(43,600,000)	8,400,000
Income taxes			110,700,000	30,200,000
State
Reconciliation of Provision of Income Taxes [Line Items]
Current			1,100,000	1,200,000
Deferred			200,000	(300,000)
Income taxes			1,300,000	900,000
Foreign
Reconciliation of Provision of Income Taxes [Line Items]
Current			(300,000)	200,000
Income taxes			$ (300,000)	$ 200,000