Securities (Summary Of Securities Available For Sale In Unrealized Loss Position) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Estimated Fair Value	$ 74,570	$ 115,357
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(737)	(3,212)
12 months or more, Estimated Fair Value	31,365	17,113
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1,035)	(356)
Total Estimated Fair Value	105,935	132,470
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(1,772)	(3,568)
Temporarily Impaired Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Estimated Fair Value	74,570	115,357
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(737)	(3,212)
12 months or more, Estimated Fair Value	31,365	17,113
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1,035)	(356)
Total Estimated Fair Value	105,935	132,470
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(1,772)	(3,568)
Temporarily Impaired Securities [Member] | U S Government Corporations And Agencies Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Estimated Fair Value	5,374	763
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(25)	(5)
12 months or more, Estimated Fair Value	2,712	2,575
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(39)	(43)
Total Estimated Fair Value	8,086	3,338
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(64)	(48)
Temporarily Impaired Securities [Member] | Government Sponsored Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Estimated Fair Value	29,222	55,388
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(316)	(985)
12 months or more, Estimated Fair Value	13,476	8,389
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(403)	(174)
Total Estimated Fair Value	42,698	63,777
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(719)	(1,159)
Temporarily Impaired Securities [Member] | Nongovernment Sponsored Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Estimated Fair Value	0	97
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
12 months or more, Estimated Fair Value	949	3,013
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(8)	(22)
Total Estimated Fair Value	949	3,110
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(8)	(22)
Temporarily Impaired Securities [Member] | State and Political Subdivisions General Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Estimated Fair Value	734
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1)
12 months or more, Estimated Fair Value	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Total Estimated Fair Value	734
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(1)
Temporarily Impaired Securities [Member] | State and Political Subdivisions Other Revenues [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Estimated Fair Value	4,816
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(29)
12 months or more, Estimated Fair Value	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Total Estimated Fair Value	4,816
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(29)
Temporarily Impaired Securities [Member] | Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Estimated Fair Value	3,014	968
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(39)	(31)
12 months or more, Estimated Fair Value	1,653	3,136
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(97)	(117)
Total Estimated Fair Value	4,667	4,104
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(136)	(148)
Temporarily Impaired Securities [Member] | Tax Exempt State and Political Subdivisions General Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Estimated Fair Value	14,204	33,115
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(164)	(1,388)
12 months or more, Estimated Fair Value	10,236	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(346)	0
Total Estimated Fair Value	24,440	33,115
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(510)	(1,388)
Temporarily Impaired Securities [Member] | Tax Exempt State and Political Subdivisions Water and Sewer Revenues [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Estimated Fair Value	6,702	4,761
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(74)	(149)
12 months or more, Estimated Fair Value	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Total Estimated Fair Value	6,702	4,761
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(74)	(149)
Temporarily Impaired Securities [Member] | Tax Exempt State and Political Subdivisions Lease Revenues [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Estimated Fair Value	571	7,011
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(2)	(201)
12 months or more, Estimated Fair Value	1,061	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(69)	0
Total Estimated Fair Value	1,632	7,011
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(71)	(201)
Temporarily Impaired Securities [Member] | Tax Exempt State and Political Subdivisions Electric Revenues [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Estimated Fair Value	2,146	1,973
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(23)	(48)
12 months or more, Estimated Fair Value	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Total Estimated Fair Value	2,146	1,973
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(23)	(48)
Temporarily Impaired Securities [Member] | Tax Exempt State and Political Subdivisions Sales Tax Revenues [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Estimated Fair Value		2,836
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		(34)
12 months or more, Estimated Fair Value		0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		0
Total Estimated Fair Value		2,836
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		(34)
Temporarily Impaired Securities [Member] | Tax Exempt State and Political Subdivisions University Revenues [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Estimated Fair Value	3,508
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(22)
12 months or more, Estimated Fair Value	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Total Estimated Fair Value	3,508
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(22)
Temporarily Impaired Securities [Member] | Tax Exempt State and Political Subdivisions Other Revenues [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Estimated Fair Value	4,279	8,445
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(42)	(371)
12 months or more, Estimated Fair Value	1,278	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(73)	0
Total Estimated Fair Value	5,557	8,445
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (115)	$ (371)