Components Of Income Tax Expense (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Tax Expenses [Line Items]
Current income tax expense, Federal	$ 75,940	$ 71,230	$ 63,056
Current income tax expense, State	5,885	6,466	5,506
Current income tax expense, Total	81,825	77,696	68,562
Deferred income tax expense, Federal	8,576	17,167	24,035
Deferred income tax expense, State	(2,815)	2,154	2,168
Deferred income tax expense, Total	5,761	19,321	26,203
Income tax expense	$ 87,586	$ 97,017	$ 94,765