Comprehensive Income Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Before-Tax Amount
Other Comprehensive Income	$ 5,300	$ 3,007
Tax (Expense) Benefit
Other Comprehensive Income	(1,355)	(764)
Net of Tax Amount
Net Unrealized Securities Holding Gains on Securities Available-for-Sale Arising During the Period	3,879	2,080
Amortization of Net Retirement Plan	66	163
Other Comprehensive Income	3,945	2,243
Unrealized Gains and Losses on Available for Sale Securities
Before-Tax Amount
Net Unrealized Securities Holding Gains on Securities Available-for-Sale Arising During the Period	5,504	2,788
Tax (Expense) Benefit
Net Unrealized Securities Holding Gains on Securities Available-for-Sale Arising During the Period	(1,406)	(708)
Net of Tax Amount
Net Unrealized Securities Holding Gains on Securities Available-for-Sale Arising During the Period	4,098	2,080
Amortization of Net Retirement Plan	0	0
Unrealized Loss on Cash Flow Swap
Before-Tax Amount
Net Unrealized Losses on Cash Flow Swap	(294)
Tax (Expense) Benefit
Net Unrealized Losses on Cash Flow Swap	75
Net of Tax Amount
Net Unrealized Securities Holding Gains on Securities Available-for-Sale Arising During the Period	(219)
Net Unrealized Losses on Cash Flow Swap	(219)
Amortization of Net Retirement Plan	0
Amortization of Net Retirement Plan Actuarial Gain (Loss)
Before-Tax Amount
Amortization of Net Retirement Plan	36	163
Tax (Expense) Benefit
Amortization of Net Retirement Plan	(9)	(42)
Net of Tax Amount
Net Unrealized Securities Holding Gains on Securities Available-for-Sale Arising During the Period	0	0
Amortization of Net Retirement Plan	27	121
Accumulated Defined Benefit Plans Adjustment, Net Prior Service
Before-Tax Amount
Amortization of Net Retirement Plan	54	56
Tax (Expense) Benefit
Amortization of Net Retirement Plan	(15)	(14)
Net of Tax Amount
Amortization of Net Retirement Plan	$ 39	$ 42