Accumulated Balances Related Component of Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 30,656	$ 29,968
Ending balance	55,466	30,656
Unrealized Gains And Losses On Available for Sale Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(116)	(182)
Other comprehensive income (loss) before reclassifications	(218)	130
Amounts reclassified from accumulated other comprehensive income (loss)	(240)	(64)
Ending balance	(574)	(116)
Defined Benefit Pension Items
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(608)	(405)
Other comprehensive income (loss) before reclassifications	(172)	(203)
Ending balance	(780)	(608)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(724)	(587)
Other comprehensive income (loss) before reclassifications	(390)	(73)
Amounts reclassified from accumulated other comprehensive income (loss)	(240)	(64)
Ending balance	$ (1,354)	$ (724)