Accumulated Other Comprehensive Income - Balances in Accumulated Other Comprehensive Income (Loss) (Parenthetical) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Unrealized holding gains (losses) arising during the period, tax expense	$ 136	$ 60	$ 47	$ 340
Reclassification for previously unrealized net losses recognized in income, tax benefit	0	(3)	1	(9)
Holding gains (losses) on securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Unrealized holding gains (losses) arising during the period, tax expense	136	60	47	340
Reclassification for previously unrealized net losses recognized in income, tax benefit	$ 0	$ (3)	$ 1	$ (9)