Accumulated Other Comprehensive Income - Balances in Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	$ 39,569	$ 39,238
Other comprehensive income before reclassifications, net of tax expense (benefit)	(340)	90
Reclassification for previously unrealized net gains recognized in income, net of tax expense	(287)	(28)
Net gain on pension and postretirement plans, net of tax expense	168	83
Balance at end of period	41,705	39,569
Net Unrealized Gains (Losses) on Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	107	45
Other comprehensive income before reclassifications, net of tax expense (benefit)	(340)	90
Reclassification for previously unrealized net gains recognized in income, net of tax expense	(287)	(28)
Balance at end of period	(520)	107
Pension and Post employment costs
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(883)	(966)
Net gain on pension and postretirement plans, net of tax expense	168	83
Balance at end of period	(715)	(883)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(776)	(921)
Balance at end of period	$ (1,235)	$ (776)