Accumulated Other Comprehensive Income (Loss) - Significant Amounts Reclassified Out of Each Component of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net gain on sales of available for sale securities	$ 346	$ 82
Compensation and employee benefits	(9,258)	(8,630)
Tax effect	(2,114)	(1,248)
Net income	4,277	3,986
Amount Reclassified From Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net income	219	(91)
Amount Reclassified From Accumulated Other Comprehensive Income | Unrealized gains and losses on available-for-sale securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net gain on sales of available for sale securities	(346)	82
Other than temporary impairment losses	508
Tax effect	(55)	(28)
Net income	107	54
Amount Reclassified From Accumulated Other Comprehensive Income | Amortization of defined benefit pension items
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Compensation and employee benefits	239	(220)
Tax effect	(127)	75
Net income	112	(145)
Amount Reclassified From Accumulated Other Comprehensive Income | Prior service costs
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Compensation and employee benefits	0	23
Amount Reclassified From Accumulated Other Comprehensive Income | Actuarial gains
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Compensation and employee benefits	$ 239	$ (243)