Other Comprehensive Income (Loss) (Schedule of AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance			$ 364,571
Other Comprehensive Income (Loss) Before Reclassification	$ (3,850)	$ (937)	(14,298)	$ 9,627
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(71)	(374)	(342)	(374)
Net Current Period Other Comprehensive Income (Loss)	(3,921)	(1,311)	(14,640)	9,253
Ending Balance	376,123		376,123
Unrealized Gains and Losses on Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(13,054)	4,252	(2,335)	(6,312)
Other Comprehensive Income (Loss) Before Reclassification	(3,850)	(937)	(14,298)	9,627
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(71)	(374)	(342)	(374)
Net Current Period Other Comprehensive Income (Loss)	(3,921)	(1,311)	(14,640)	9,253
Ending Balance	(16,975)	2,941	(16,975)	2,941
Postretirement Benefit Items
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(285)	(92)	(285)	(92)
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	(285)	(92)	(285)	(92)
Total
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(13,339)	4,160	(2,620)	(6,404)
Ending Balance	$ (17,260)	$ 2,849	$ (17,260)	$ 2,849