Investment Securities - Realized Gains and Losses on Sales of Investment Securities (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Investments, Debt and Equity Securities [Abstract]
Gross gains, Sales transactions	$ 0	$ 0	$ 3,274	$ 0
Gross losses, sales transactions	0	0	(947)	0
Gains (losses) on Sales transactions, net	0	0	2,327	0
Gross gains, Maturities and other securities transactions	40	7	129	8
Gross losses, Maturities and other securities transactions	(132)	0	(132)	(9)
Gains (losses) on Maturities and other securities transactions, net	(92)	7	(3)	(1)
Total (losses) gains on securities transactions, net	$ (92)	$ 7	$ 2,324	$ (1)