Other Comprehensive Income (Loss) (Changes in AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balances	$ 617,213	$ 624,709	$ 583,540	$ 573,820	$ 624,709	$ 573,820
Other Comprehensive Income (Loss) Before Reclassification	13,115		3,573		(7,949)	17,291
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(237)		(784)		(1,001)	(1,247)
Total Other Comprehensive Income (Loss)	12,878	(21,828)	2,789	13,255	(8,950)	16,044
Ending Balances	648,997	617,213	594,674	583,540	648,997	594,674
Unrealized Gains and Losses on Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balances	14,115	35,943	28,928	15,673	35,943	15,673
Other Comprehensive Income (Loss) Before Reclassification	13,115		3,573		(7,949)	17,291
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(237)		(784)		(1,001)	(1,247)
Total Other Comprehensive Income (Loss)	12,878		2,789		(8,950)	16,044
Ending Balances	26,993	14,115	31,717	28,928	26,993	31,717
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	13,547	35,375	28,360	15,105	35,375	15,105
Total Other Comprehensive Income (Loss)	12,878	(21,828)	2,789	13,255
Ending Balances	$ 26,425	$ 13,547	$ 31,149	$ 28,360	$ 26,425	$ 31,149