Comprehensive Income (Loss), Net of Tax - Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Before-Tax Amount
Other comprehensive income (loss)	$ 9,993	$ (6,657)	$ (370)
Tax Expense (Benefit)
Other comprehensive income (loss)	(2,540)	1,692	335
Net-of-Tax Amount
Net Unrealized Securities Holding Gains Arising During the Period	6,776	(5,287)	(726)
Amortization of Net Retirement Plan	677	322	691
Other comprehensive income (loss)	7,453	(4,965)	(35)
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent
Before-Tax Amount
Net Unrealized Securities Holding Gains Arising During the Period	5,580	(2,839)	(1,505)
Amortization of Net Retirement Plan			448
Tax Expense (Benefit)
Net Unrealized Securities Holding Gains Arising During the Period	(1,418)	723	565
Amortization of Net Retirement Plan			(111)
Net-of-Tax Amount
Net Unrealized Securities Holding Gains Arising During the Period	4,162	(2,116)	(940)
Amortization of Net Retirement Plan		0	337
Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) Attributable to Parent
Before-Tax Amount
Net Unrealized Securities Holding Gains Arising During the Period	3,505	(3,798)	287
Amortization of Net Retirement Plan	684	325	411
Tax Expense (Benefit)
Net Unrealized Securities Holding Gains Arising During the Period	(891)	965	(73)
Amortization of Net Retirement Plan	(174)	(83)	(49)
Net-of-Tax Amount
Net Unrealized Securities Holding Gains Arising During the Period	2,614	(2,833)	214
Amortization of Net Retirement Plan	510	242	362
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Including Portion Attributable to Noncontrolling Interest
Before-Tax Amount
Net Retirement Plan Prior Service Credit		(453)
Amortization of Net Retirement Plan	224	108	(11)
Tax Expense (Benefit)
Net Unrealized Securities Holding Gains Arising During the Period		115
Amortization of Net Retirement Plan	(57)	(28)	3
Net-of-Tax Amount
Net Retirement Plan Prior Service Credit		(338)
Amortization of Net Retirement Plan	$ 167	$ 80	$ (8)