Income Taxes - Income Tax Expense (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Income Tax Disclosure [Abstract]
Current income tax expense	$ 9,959	$ 18,114	$ 37,983	$ 55,631
Deferred income tax expense (benefit)	2,010	(1,043)	271	(5,020)
Income tax expense, as reported	$ 11,969	$ 17,071	$ 38,254	$ 50,611
Effective tax rate	16.50%	22.50%	17.90%	22.20%