Accumulated Other Comprehensive (Loss) Income - Components of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 575,107	$ 533,061	$ 564,704	$ 528,119
Other comprehensive income (loss)	4,978	(1,527)	9,213	(6,777)
Ending balance	590,155	542,503	590,155	542,503
Net Change in Unrealized Gains on Available-for- Sale Investment Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(2,010)	(8,157)	(6,229)	(2,861)
Other comprehensive income (loss)	4,962	(1,512)	9,181	(6,808)
Ending balance	2,952	(9,669)	2,952	(9,669)
Net Change in Unfunded Pension Liability
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,268)	(1,507)	(1,284)	(1,553)
Other comprehensive income (loss)	16	(15)	32	31
Ending balance	(1,252)	(1,522)	(1,252)	(1,522)
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(3,278)	(9,664)	(7,513)	(4,414)
Other comprehensive income (loss)	4,978	(1,527)	9,213	(6,777)
Ending balance	$ 1,700	$ (11,191)	$ 1,700	$ (11,191)