Accumulated Other Comprehensive Loss (Schedule of Changes In Each Component of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Equity [Abstract]
Combined Federal and state income tax rate	23.00%	37.00%
Accumulated Other Comprehensive Income (Loss)
Beginning Balance	$ 502,507	$ 442,438
Other comprehensive income before reclassifications	(8,218)	3,571
Amounts reclassified from other comprehensive loss	0	(2,698)
Other comprehensive income	(8,218)	873
Adoption of new accounting pronouncement	0
Ending balance	491,877	481,646
Defined Benefit Pension Plans
Accumulated Other Comprehensive Income (Loss)
Beginning Balance	(5,033)	(4,660)
Ending balance	(5,033)	(4,660)
Unrealized Gain (Losses) on Securities Available-for-Sale
Accumulated Other Comprehensive Income (Loss)
Beginning Balance	(611)	(2,352)
Other comprehensive income before reclassifications	(8,218)	3,571
Amounts reclassified from other comprehensive loss	0	(2,698)
Other comprehensive income	(8,218)	873
Ending balance	(11,486)	(1,479)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss)
Beginning Balance	(5,644)	(7,012)
Other comprehensive income	(8,218)	873
Ending balance	(16,519)	$ (6,139)
Accounting Standards Update 2016-01 | Unrealized Gain (Losses) on Securities Available-for-Sale
Accumulated Other Comprehensive Income (Loss)
Adoption of new accounting pronouncement	2,657
Accounting Standards Update 2016-01 | Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss)
Adoption of new accounting pronouncement	$ 2,657