Income Taxes - Summary of Income Tax Reconciliation (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended												12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule Of Effective Income Tax Rate Reconciliation [Line Items]
Federal income tax at expected statutory rate													$ 73,631	$ 68,326	$ 64,727
Tax-exempt interest, net of interest incurred to carry tax-exempt securities													(4,478)	(3,736)	(3,451)
Bank owned life insurance													(2,399)	(2,583)	(2,158)
State income tax expense, net of federal tax effect													8,204	12,727	629
Tax credits													(10,070)	(12,760)	(5,071)
Other, net													1,860	732	253
Income tax expense	$ 14,702	$ 22,402	$ 14,366	$ 15,278	$ 7,321	[1]	$ 13,489	[1]	$ 24,999	[1]	$ 16,897	[1]	$ 66,748	$ 62,706	$ 54,929

[1] Previously reported amounts have been revised to reflect an increase in non-interest expense due to the immaterial correction of an error. See the "Correction of an Immaterial Error" section of Note 1 to the consolidated financial statements for additional information.