Accumulated Other Comprehensive Income - Balances in Accumulated Other Comprehensive Income (Loss) (Parenthetical) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Unrealized holding gains arising during the period, tax expense	$ 46	$ 422
Reclassification for previously unrealized net losses (gains) recognized in income,tax expense (benefit)	14	(9)
Net gain (loss) pension and postretirement plans, tax expense (benefit)	42	(301)
Holding gains (losses) on securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Unrealized holding gains arising during the period, tax expense	46	422
Reclassification for previously unrealized net losses (gains) recognized in income,tax expense (benefit)	14	(9)
Pension and Post employment costs
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gain (loss) pension and postretirement plans, tax expense (benefit)	$ 42	$ (301)