Accumulated Other Comprehensive Loss - Components of Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 528,119	$ 381,127	$ 365,711
Other comprehensive (loss) income	(3,099)	(1,223)	(1,997)
Reclassification due to the adoption of ASU No. 2018-02		(782)
Ending Balance	564,704	528,119	381,127
Net Change in Unrealized Gains on Available-for-Sale Investment Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(2,861)	(1,231)	774
Other comprehensive (loss) income	(3,368)	(1,123)	(2,005)
Reclassification due to the adoption of ASU No. 2018-02		(507)
Ending Balance	(6,229)	(2,861)	(1,231)
Net Change in Unfunded Pension Liability
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(1,553)	(1,178)	(1,186)
Other comprehensive (loss) income	269	(100)	8
Reclassification due to the adoption of ASU No. 2018-02		(275)
Ending Balance	(1,284)	(1,553)	(1,178)
Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(4,414)	(2,409)	(412)
Other comprehensive (loss) income	(3,099)	(1,223)	(1,997)
Ending Balance	$ (7,513)	$ (4,414)	$ (2,409)