Other Comprehensive Income (Loss) - Summary of Components of OCI (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Investment securities available-for-sale: Before-Tax
Net change in fair value recorded in accumulated OCI, Before-Tax	$ 69,661	$ (88,562)	$ 3,074
Net realized gains reclassified into earnings, Before-Tax	0	(2,094)	0
Net change, Before-Tax	69,661	(90,656)	3,074
Investment securities available-for-sale: Tax Effect
Net change in fair value recorded in accumulated OCI, Tax Effect	29,256	(37,196)	1,292
Net realized gains reclassified into earnings, Tax Effect	0	(879)
Net change, Tax Effect	29,256	(38,075)	1,292
Investment securities available-for-sale: After-Tax
Net change in fair value recorded in accumulated OCI, After-Tax	40,405	(51,366)	1,782
Net realized gains reclassified into earnings, After-Tax	0	(1,215)
Net change, After-Tax	40,405	(52,581)	1,782
Net change in fair value recorded in accumulated OCI, After-Tax	40,405	(51,366)	1,782
Net change in fair value recorded in accumulated OCI, Before-Tax	69,661	(88,562)	3,074
Net change, After-Tax	40,405	(52,581)	1,782
Net change, Before-Tax	69,661	(90,656)	3,074
Net change in fair value recorded in accumulated OCI, Tax Effect	29,256	(37,196)	1,292
Net change, Tax Effect	$ 29,256	$ (38,075)	$ 1,292

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