Investment Securities - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Held-to-maturity Securities Pledged as Collateral	$ 16,500
Proceeds from Sale of Available-for-sale Securities	0	$ 132,868
Available-for-sale securities pledged as collateral	$ 480,100		$ 563,200