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, 2015	Dec. 31, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gains (losses) on sale of securities available-for-securities	$ 42	$ (25)
Salaries and employee benefits	(8,001)	(6,458)
Tax (expense) benefit	187	(557)
Holding gains (losses) on securities | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gains (losses) on sale of securities available-for-securities	42	(25)
Tax (expense) benefit	(14)	9
Impact on net income	28	(16)
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	(76)	(37)
Tax (expense) benefit	29	13
Impact on net income	$ (47)	$ (24)