Securities - Gross Realized Gains and Gross Realized Losses on Sales of Securities (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Schedule of Available-for-sale Securities [Line Items]
Gross realized gains	$ 3	$ 3	$ 27	$ 8
Gross realized losses	(1)	(11)	(23)	(33)
Net realized gains (losses)	2	(8)	4	(25)
Aggregate proceeds	$ 1,995	$ 479	$ 4,819	$ 3,810