Other Comprehensive Income (Loss) (Changes in AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	$ 594,674	$ 583,540	$ 573,820	$ 499,411	$ 479,187	$ 458,640	$ 573,820	$ 458,640
Other Comprehensive Income (Loss) Before Reclassification	74			4,896			17,364	23,731
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(480)			(247)			(1,726)	(777)
Total Other Comprehensive Income (Loss)	(406)	2,789	13,255	4,649	8,891	9,414	15,638	22,954
Ending Balance	603,981	594,674	583,540	562,927	499,411	479,187	603,981	562,927
Unrealized Gains and Losses on Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	31,717		15,673	11,546		(6,759)	15,673	(6,759)
Other Comprehensive Income (Loss) Before Reclassification	74			4,896			17,364	23,731
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(480)			(247)			(1,726)	(777)
Total Other Comprehensive Income (Loss)	(406)			4,649			15,638	22,954
Ending Balance	31,311	31,717		16,195	11,546		31,311	16,195
Postretirement Benefit Items
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(568)		(568)	(339)		(339)	(568)	(339)
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 Balance	(568)	(568)		(339)	(339)		(568)	(339)
Total
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	31,149	28,360	15,105	11,207	2,316	(7,098)	15,105	(7,098)
Total Other Comprehensive Income (Loss)	(406)	2,789	13,255	4,649	8,891	9,414
Ending Balance	$ 30,743	$ 31,149	$ 28,360	$ 15,856	$ 11,207	$ 2,316	$ 30,743	$ 15,856