Other Comprehensive Income (Loss) (Schedule of AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	$ 458,640	$ 364,571
Other Comprehensive Income (Loss) Before Reclassification	9,536	(9,005)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(122)	(213)
Net Current Period Other Comprehensive Income (Loss)	9,414	(9,218)
Ending Balance	479,187	364,005
Unrealized Gains and Losses on Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(6,759)	(2,335)
Other Comprehensive Income (Loss) Before Reclassification	9,536	(9,005)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(122)	(213)
Net Current Period Other Comprehensive Income (Loss)	9,414	(9,218)
Ending Balance	2,655	(11,553)
Postretirement Benefit Items
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(339)	(285)
Other Comprehensive Income (Loss) Before Reclassification	0	0
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	0	0
Net Current Period Other Comprehensive Income (Loss)	0	0
Ending Balance	(339)	(285)
Total
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(7,098)	(2,620)
Ending Balance	$ 2,316	$ (11,838)