Other Comprehensive Income (Loss) (Schedule of AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance			$ 364,571
Other Comprehensive Income (Loss) Before Reclassification	$ (1,443)	$ 6,566	(10,448)	$ 10,564
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(58)	0	(271)	0
Net Current Period Other Comprehensive Income (Loss)	(1,501)	6,566	(10,719)	10,564
Ending Balance	370,540		370,540
Unrealized Gains and Losses on Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(11,553)	(2,314)	(2,335)	(6,312)
Other Comprehensive Income (Loss) Before Reclassification	(1,443)	6,566	(10,448)	10,564
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(58)	0	(271)	0
Net Current Period Other Comprehensive Income (Loss)	(1,501)	6,566	(10,719)	10,564
Ending Balance	(13,054)	4,252	(13,054)	4,252
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	(11,838)	(2,406)	(2,620)	(6,404)
Ending Balance	$ (13,339)	$ 4,160	$ (13,339)	$ 4,160