Other Comprehensive Income - Summary of Components of Other Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Equity [Abstract]
Net change in fair value recorded in accumulated OCI, Before-tax	$ 7,579	$ (32,968)	$ 35,623	$ (12,698)
Net change in fair value recorded in accumulated OCI, Tax effect	3,183	(13,846)	14,961	(5,332)
Net change in fair value recorded in accumulated OCI, After-tax	4,396	(19,122)	20,662	(7,366)
Amortization of unrealized gains on securities transferred from available-for-sale to held-to-maturity, Before-tax	(86)	0	(860)	0
Amortization of unrealized gains on securities transferred from available-for-sale to held-to-maturity, Tax effect	(36)	0	(361)	0
Amortization of unrealized gains on securities transferred from available-for-sale to held-to-maturity, After-tax	(50)	0	(499)	0
Net realized loss reclassified into earnings, Before-Tax	0	0	0	0
Net realized loss reclassified into earnings, Tax Effect	0	0	0	0
Net realized loss reclassified into earnings, After-Tax	0	0	0	0
Net change, Before-tax	7,493	(32,968)	34,763	(12,698)
Net change, Tax effect	3,147	(13,846)	14,600	(5,332)
Net change, After-tax	$ 4,346	$ (19,122)	$ 20,163	$ (7,366)