Securities - Carrying Value of Held-to-Maturity Investment Securities (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Amortized Cost	$ 704,767	$ 607,833
Net loss on date of transfer from available-for-sale	(13,347)	(13,347)
Accretion of net unrealized loss on securities reclassified as held-to-maturity	4,498	4,205
Carrying value	$ 695,918	$ 598,691