Other Comprehensive Income (Loss) (Schedule of Other Comprehensive Income Components) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	$ 330,267	$ 252,348	$ 228,824
Other Comprehensive Income (Loss) Before Reclassification	4,635	(8,934)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(382)	(1,282)
Comprehensive Income (Loss)	4,253	(10,216)
ASU 2018-02 Adoption	(469)
Ending Balance	364,571	330,267	252,348
Unrealized Gains and Losses on Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(6,312)	3,890
Other Comprehensive Income (Loss) Before Reclassification	4,778	(8,916)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(387)	(1,286)
Comprehensive Income (Loss)	4,391	(10,202)
ASU 2018-02 Adoption	(414)
Ending Balance	(2,335)	(6,312)	3,890
Postretirement Benefit Items
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(92)	(78)
Other Comprehensive Income (Loss) Before Reclassification	(143)	(18)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	5	4
Comprehensive Income (Loss)	(138)	(14)
ASU 2018-02 Adoption	(55)
Ending Balance	(285)	(92)	(78)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(6,404)	3,812	2,890
Ending Balance	$ (2,620)	$ (6,404)	$ 3,812