Investment Securities - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Held-to-maturity Securities Pledged as Collateral	$ 281,900		$ 45,700
Proceeds from Sale of Available-for-sale Securities	55,744	$ 0
Available-for-sale securities pledged as collateral	$ 498,500		$ 416,100