Other Comprehensive Income - Summary of Components of Other Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Equity [Abstract]
Net change in fair value recorded in accumulated OCI, Before-tax	$ 2,083	$ (4,006)	$ 6,128	$ 31,617
Net change in fair value recorded in accumulated OCI, Tax effect	875	(1,683)	2,574	13,279
Net change in fair value recorded in accumulated OCI, After-tax	1,208	(2,323)	3,554	18,338
Amortization of unrealized gain (loss) on securities transferred from available-for-sale to held-to-maturity, Before-tax	(862)	297	(2,841)	(563)
Amortization of unrealized gain (loss) on securities transferred from available-for-sale to held-to-maturity, Tax effect	(362)	125	(1,193)	(237)
Amortization of unrealized gain (loss) on securities transferred from available-for-sale to held-to-maturity, After-tax	(500)	172	(1,648)	(326)
Net realized gain reclassified into earnings, Before-tax	0	(548)	(402)	(548)
Net realized gain reclassified into earnings, Tax Effect	0	(230)	(169)	(230)
Net realized gain reclassified into earnings, After-Tax	0	(318)	(233)	(318)
Net Change, Before-tax	1,221	(4,257)	2,885	30,506
Net Change, Tax effect	513	(1,788)	1,212	12,812
Other comprehensive income, net of tax	$ 708	$ (2,469)	$ 1,673	$ 17,694