Accumulated Other Comprehensive Loss, net - Reclassification for Previously Unrealized Gains or Losses on Available-for-sale Securities and Pension and Post-retirement Benefit Plan-related Costs (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Salaries and employee benefits	$ (16,233)	$ (13,403)
Tax benefit	$ (533)	(797)
Holding Gains (Losses) on Available-for-sale Securities | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net gains on sale of available-for-sale securities		2
Impact on net income		2
Pension and Post-retirement Benefit Plan Costs | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Salaries and employee benefits		(81)
Tax benefit		28
Impact on net income		$ (53)