Investment Securities - Realized Gains and Losses on Sales of Investment Securities (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Investments, Debt and Equity Securities [Abstract]
Gross gains, Sales transactions	$ 0	$ 103	$ 3,274	$ 103
Gross losses, sales transactions	0	0	(947)	0
Gains (losses) on Sales transactions, net	0	103	2,327	103
Gross gains, Maturities and other securities transactions	158	0	287	8
Gross losses, Maturities and other securities transactions	(1)	0	(133)	(9)
Gains (losses) on Maturities and other securities transactions, net	157	0	154	(1)
Total gains on securities transactions, net	$ 157	$ 103	$ 2,481	$ 102