Other Comprehensive Income (Loss) (Changes in AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balances	$ 648,997	$ 617,213	$ 624,709	$ 594,674	$ 583,540	$ 573,820	$ 624,709	$ 573,820
Other Comprehensive Income (Loss) Before Reclassification	(14,989)			74			(22,932)	17,364
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(172)			(480)			(1,179)	(1,726)
Total Other Comprehensive Income (Loss)	(15,161)	12,878	(21,828)	(406)	2,789	13,255	(24,111)	15,638
Ending Balances	650,139	648,997	617,213	603,981	594,674	583,540	650,139	603,981
Unrealized Gains and Losses on Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balances	26,993		35,943	31,717		15,673	35,943	15,673
Other Comprehensive Income (Loss) Before Reclassification	(14,989)			74			(22,932)	17,364
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(172)			(480)			(1,179)	(1,726)
Total Other Comprehensive Income (Loss)	(15,161)			(406)			(24,111)	15,638
Ending Balances	11,832	26,993		31,311	31,717		11,832	31,311
Postretirement Benefit Items
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balances	(568)		(568)	(568)		(568)	(568)	(568)
Other Comprehensive Income (Loss) Before Reclassification	0			0			0	0
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	0			0			0	0
Total Other Comprehensive Income (Loss)	0			0			0	0
Ending Balances	(568)	(568)		(568)	(568)		(568)	(568)
Total
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balances	26,425	13,547	35,375	31,149	28,360	15,105	35,375	15,105
Total Other Comprehensive Income (Loss)	(15,161)	12,878	(21,828)	(406)	2,789	13,255
Ending Balances	$ 11,264	$ 26,425	$ 13,547	$ 30,743	$ 31,149	$ 28,360	$ 11,264	$ 30,743