Other Comprehensive Income - Summary of Components of OCI (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Equity [Abstract]
Net change in fair value recorded in accumulated OCI, Before-tax	$ 36,619	$ 19,350
Net change in fair value recorded in accumulated OCI, Tax effect	(10,826)	(5,720)
Net change in fair value recorded in accumulated OCI, After-tax	25,793	13,630
Amortization of unrealized losses on securities transferred from available-for-sale to held-to-maturity, Before-tax	(1)	(1,123)
Amortization of unrealized losses on securities transferred from available-for-sale to held-to-maturity, Tax effect	0	332
Amortization of unrealized losses on securities transferred from available-for-sale to held-to-maturity, After-tax	(1)	(791)
Net change, Before-tax	36,618	18,227
Net change, Tax effect	(10,826)	(5,388)
Net change, After-tax	$ 25,792	$ 12,839