Comprehensive Income - Summary of Reclassifications Out of Accumulated Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net securities gains	$ 9,461	$ 684
Tax (expense) benefit	14,199	11,827
Net Income	34,524	28,538
Amount Reclassified from Other Comprehensive Income [Member] | Unrealized Net Gains (Losses) on Securities Available for Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net securities gains	(9,461)
Tax (expense) benefit	(3,311)
Net Income	$ (6,150)