Other Comprehensive Income (Loss) (Schedule of AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	$ 479,187	$ 364,005	$ 458,640	$ 364,571
Other Comprehensive Income (Loss) Before Reclassification	9,299	(1,443)	18,835	(10,448)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(408)	(58)	(530)	(271)
Net Current Period Other Comprehensive Income (Loss)	8,891	(1,501)	18,305	(10,719)
Ending Balance	499,411	370,540	499,411	370,540
Unrealized Gains and Losses on Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	2,655	(11,553)	(6,759)	(2,335)
Other Comprehensive Income (Loss) Before Reclassification	9,299	(1,443)	18,835	(10,448)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(408)	(58)	(530)	(271)
Net Current Period Other Comprehensive Income (Loss)	8,891	(1,501)	18,305	(10,719)
Ending Balance	11,546	(13,054)	11,546	(13,054)
Postretirement Benefit Items
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(339)	(285)	(339)	(285)
Other Comprehensive Income (Loss) Before Reclassification	0	0	0	0
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	0	0	0	0
Net Current Period Other Comprehensive Income (Loss)	0	0	0	0
Ending Balance	(339)	(285)	(339)	(285)
Total
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	2,316	(11,838)	(7,098)	(2,620)
Ending Balance	$ 11,207	$ (13,339)	$ 11,207	$ (13,339)