Other Comprehensive Income/(Loss) - Summary of Changes in Accumulated Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Investment securities available-for-sale: Before-Tax
Net change in fair value recorded in accumulated OCI, Before-Tax	$ (11,696)	$ (73)
Net realized gains reclassified into earnings, Before-Tax	(2,094)
Net change, Before-Tax	(13,790)	(73)
Investment securities available-for-sale: Tax Effect
Net change in fair value recorded in accumulated OCI,Tax Effect	(4,913)
Net realized gains reclassified into earnings,Tax Effect	(879)
Net change, Tax Effect	(5,792)	(31)
Investment securities available-for-sale: After-Tax
Net change in fair value recorded in accumulated OCI, After-Tax	(6,783)
Net realized gains reclassified into earnings, After-Tax	(1,215)
Other comprehensive loss, net of tax	$ (7,998)	$ (42)

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