Changes in Accumulated Other Comprehensive Income (Loss) - Balances in Accumulated Other Comprehensive Income (Loss) (Parenthetical) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Change in net unrealized holding gains on securities, before reclassification, tax expense	$ 150	$ 130	$ 164	$ 303
Reclassification for previously unrealized net (gains) losses recognized in income, tax expense (benefit)	$ 2	$ 35	$ 1	$ 37