Accumulated Other Comprehensive Loss (Schedule of Changes In Each Component of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Equity [Abstract]
Combined Federal and state income tax rate	23.00%	37.00%	23.00%	37.00%
Accumulated Other Comprehensive (Loss) Income
Beginning Balance	$ 503,753	$ 492,507	$ 502,507	$ 442,438
Other comprehensive income before reclassifications			(14,976)	5,933
Amounts reclassified from other comprehensive loss			0	(2,698)
Other comprehensive income	(4,325)	308	(14,976)	3,235
Adoption of new accounting pronouncement			0
Ending balance	512,026	500,315	512,026	500,315
Defined Benefit Pension Plans
Accumulated Other Comprehensive (Loss) Income
Beginning Balance			(5,033)	(4,660)
Ending balance	(5,033)	(4,660)	(5,033)	(4,660)
Unrealized Gain (Losses) on Securities Available-for-Sale
Accumulated Other Comprehensive (Loss) Income
Beginning Balance			(611)	(2,352)
Other comprehensive income before reclassifications			(14,976)	5,933
Amounts reclassified from other comprehensive loss			0	(2,698)
Other comprehensive income			(14,976)	3,235
Adoption of new accounting pronouncement			2,657
Ending balance	(18,244)	883	(18,244)	883
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive (Loss) Income
Beginning Balance	(18,952)	(4,085)	(5,644)	(7,012)
Other comprehensive income	(4,325)	308	(14,976)	3,235
Adoption of new accounting pronouncement			2,657
Ending balance	$ (23,277)	$ (3,777)	(23,277)	$ (3,777)
Accounting Standards Update 2016-01
Accumulated Other Comprehensive (Loss) Income
Adoption of new accounting pronouncement			2,700
Accounting Standards Update 2016-01 \| Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive (Loss) Income
Adoption of new accounting pronouncement			$ 2,657

Accumulated Other Comprehensive Income (Loss), Net of Income Tax [Roll Forward]

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Combined Federal And State Income Tax Rate

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Represents the quantification of the effect of adopting the new accounting standard or change in accounting principle expected by the entity to have a significant effect on the entity's financial statements.

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Amount after tax, before reclassification adjustments of other comprehensive income (loss).

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Amount after tax and reclassification adjustments of other comprehensive income (loss).

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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