Investment Securities - Additional Information (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Held-to-maturity Securities Pledged as Collateral	$ 11,200
Proceeds from sales	0	$ 0
Available-for-sale securities pledged as collateral	$ 530,500		$ 563,200