Other Comprehensive Income (Loss) (Schedule of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance			$ 330,267
Other Comprehensive Income (Loss) Before Reclassification	$ (937)	$ 1,228	9,627	$ 9,240
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(374)	(298)	(374)	(927)
Net Current Period Other Comprehensive Income (Loss)	(1,311)	930	9,253	8,313
Ending Balance	360,625		360,625
Unrealized Gains and Losses on Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	4,252	11,273	(6,312)	3,890
Other Comprehensive Income (Loss) Before Reclassification	(937)	1,228	9,627	9,240
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(374)	(298)	(374)	(927)
Net Current Period Other Comprehensive Income (Loss)	(1,311)	930	9,253	8,313
Ending Balance	2,941	12,203	2,941	12,203
Postretirement Benefit Items
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(92)	(78)	(92)	(78)
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	(92)	(78)	(92)	(78)
Total
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	4,160	11,195	(6,404)	3,812
Ending Balance	$ 2,849	$ 12,125	$ 2,849	$ 12,125