Accumulated Other Comprehensive Income - Reclassification for unrealized gains and impairments on securities and pension and postemployment related costs (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Salaries and employee benefits	$ (7,799)	$ (8,001)
Tax (expense) benefit	(966)	187
Net Unrealized Gains (Losses) on Securities | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gains on sale of securities available-for-securities	435	42
Tax (expense) benefit	(148)	(14)
Impact on net income	287	28
Pension and Post employment costs | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Salaries and employee benefits	(77)	(76)
Tax (expense) benefit	26	29
Impact on net income	$ (51)	$ (47)