Accumulated Other Comprehensive Income - Components of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018		Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 208,717	[1]	$ 201,380
Net unrealized gains on securities available for sale, net of tax	(2,873)		657
Reclassification adjustment for realized gains on securities, net of tax	(6)		(168)
Reclassification for ASU 2016-01 adoption					$ 0
Ending Balance	209,840		204,241
Net unrealized gains (losses) on securities available for sale, tax	(861)		354
Reclassification adjustment for realized gains on securities, tax	(2)		(91)
Net Unrealized Gains (Losses) on Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(796)		(150)
Net unrealized gains on securities available for sale, net of tax	(2,873)		657
Reclassification adjustment for realized gains on securities, net of tax	(6)		(168)
Reclassification for ASU 2016-01 adoption					(650)
Ending Balance	(4,325)		339
Adjustments Related to Pension Benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(2,280)		(1,724)
Net unrealized gains on securities available for sale, net of tax	0		0
Reclassification adjustment for realized gains on securities, net of tax	0		0
Reclassification for ASU 2016-01 adoption					0
Ending Balance	(2,280)		(1,724)
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(3,076)		(1,874)
Reclassification for ASU 2016-01 adoption				$ (650)	$ (650)
Ending Balance	$ (6,605)		$ (1,385)

[1] Derived from audited consolidated financial statements.