Income Taxes (Income Tax Expense) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Current income tax expense	$ 18,114	$ 24,036	$ 55,631	$ 50,101
Deferred income tax expense (benefit)	(1,043)	(382)	(5,020)	(137)
Income tax expense, as reported	$ 17,071	$ 23,654	$ 50,611	$ 49,964
Effective tax rate	22.50%	30.30%	22.20%	23.60%