Other Comprehensive Income (Loss) (Changes in AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	$ 583,540	$ 573,820	$ 479,187	$ 458,640	$ 573,820	$ 458,640
Other Comprehensive Income (Loss) Before Reclassification	3,573		9,299		17,291	18,835
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(784)		(408)		(1,247)	(530)
Total Other Comprehensive Income (Loss)	2,789	13,255	8,891	9,414	16,044	18,305
Ending Balance	594,674	583,540	499,411	479,187	594,674	499,411
Unrealized Gains and Losses on Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	28,928	15,673	2,655	(6,759)	15,673	(6,759)
Other Comprehensive Income (Loss) Before Reclassification	3,573		9,299		17,291	18,835
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(784)		(408)		(1,247)	(530)
Total Other Comprehensive Income (Loss)	2,789		8,891		16,044	18,305
Ending Balance	31,717	28,928	11,546	2,655	31,717	11,546
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	28,360	15,105	2,316	(7,098)	15,105	(7,098)
Total Other Comprehensive Income (Loss)	2,789	13,255	8,891	9,414
Ending Balance	$ 31,149	$ 28,360	$ 11,207	$ 2,316	$ 31,149	$ 11,207