Other Comprehensive Income (Loss) (Schedule of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance at January 1	$ 330,267
Other Comprehensive Income (Loss) Before Reclassification	3,998	$ 4,029
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	0	0
Total Other Comprehensive Income	3,998	4,029
Ending Balance at March 31	341,216
Unrealized Gains and Losses on Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance at January 1	(6,312)	3,890
Other Comprehensive Income (Loss) Before Reclassification	3,998	4,029
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	0	0
Total Other Comprehensive Income	3,998	4,029
Ending Balance at March 31	(2,314)	7,919
Postretirement Benefit Items
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance at January 1	(92)	(78)
Other Comprehensive Income (Loss) Before Reclassification	0	0
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	0	0
Total Other Comprehensive Income	0	0
Ending Balance at March 31	(92)	(78)
AOCI Including Portion Attributable to Noncontrolling Interest [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance at January 1	(6,404)	3,812
Ending Balance at March 31	$ (2,406)	$ 7,841