Comprehensive Income - Summary of Reclassifications Out of Accumulated Other Comprehensive Income (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
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net securities gains	$ 5	$ (66)	$ 757	$ 302
Tax (expense) benefit	9,977	12,090	34,024	32,549
Net Income	31,634	30,743	89,365	81,455
Amount Reclassified from Other Comprehensive Income [Member] | Unrealized Net Gains on Securities Available for Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net securities gains			(743)
Tax (expense) benefit			(260)
Net Income			$ (483)