Securities (Summary Of Securities Available For Sale In Unrealized Loss Position) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Estimated Fair Value	$ 65,199	$ 115,357
Less than 12 months, Unrealized Loss	(550)	(3,212)
12 months or more, Estimated Fair Value	37,384	17,113
12 months or more, Unrealized Loss	(964)	(356)
Total Estimated Fair Value	102,583	132,470
Total Unrealized Loss	(1,514)	(3,568)
Temporarily Impaired Securities Member
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Estimated Fair Value	65,199	115,357
Less than 12 months, Unrealized Loss	(550)	(3,212)
12 months or more, Estimated Fair Value	37,384	17,113
12 months or more, Unrealized Loss	(964)	(356)
Total Estimated Fair Value	102,583	132,470
Total Unrealized Loss	(1,514)	(3,568)
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	1,749
Less than 12 months, Unrealized Loss	(9)
12 months or more, Estimated Fair Value	0
12 months or more, Unrealized Loss	0
Total Estimated Fair Value	1,749
Total Unrealized Loss	(9)
Temporarily Impaired Securities Member | U.S. Government and agencies and corporations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Estimated Fair Value	10,864	763
Less than 12 months, Unrealized Loss	(91)	(5)
12 months or more, Estimated Fair Value	2,394	2,575
12 months or more, Unrealized Loss	(54)	(43)
Total Estimated Fair Value	13,258	3,338
Total Unrealized Loss	(145)	(48)
Temporarily Impaired Securities Member | Government-sponsored agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Estimated Fair Value	32,156	55,388
Less than 12 months, Unrealized Loss	(269)	(985)
12 months or more, Estimated Fair Value	22,584	8,389
12 months or more, Unrealized Loss	(634)	(174)
Total Estimated Fair Value	54,740	63,777
Total Unrealized Loss	(903)	(1,159)
Temporarily Impaired Securities Member | Nongovernment-sponsored entities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Estimated Fair Value	5	97
Less than 12 months, Unrealized Loss	0	0
12 months or more, Estimated Fair Value	810	3,013
12 months or more, Unrealized Loss	(7)	(22)
Total Estimated Fair Value	815	3,110
Total Unrealized Loss	(7)	(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	6,035
Less than 12 months, Unrealized Loss	(55)
12 months or more, Estimated Fair Value	0
12 months or more, Unrealized Loss	0
Total Estimated Fair Value	6,035
Total Unrealized Loss	(55)
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	7,532
Less than 12 months, Unrealized Loss	(62)
12 months or more, Estimated Fair Value	0
12 months or more, Unrealized Loss	0
Total Estimated Fair Value	7,532
Total Unrealized Loss	(62)
Temporarily Impaired Securities Member | Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Estimated Fair Value	3,008	968
Less than 12 months, Unrealized Loss	(39)	(31)
12 months or more, Estimated Fair Value	1,659	3,136
12 months or more, Unrealized Loss	(91)	(117)
Total Estimated Fair Value	4,667	4,104
Total Unrealized Loss	(130)	(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	2,999	33,115
Less than 12 months, Unrealized Loss	(20)	(1,388)
12 months or more, Estimated Fair Value	9,937	0
12 months or more, Unrealized Loss	(178)	0
Total Estimated Fair Value	12,936	33,115
Total Unrealized Loss	(198)	(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	282	4,761
Less than 12 months, Unrealized Loss	(3)	(149)
12 months or more, Estimated Fair Value	0	0
12 months or more, Unrealized Loss	0	0
Total Estimated Fair Value	282	4,761
Total Unrealized Loss	(3)	(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	569	7,011
Less than 12 months, Unrealized Loss	(2)	(201)
12 months or more, Estimated Fair Value	0	0
12 months or more, Unrealized Loss	0	0
Total Estimated Fair Value	569	7,011
Total Unrealized Loss	$ (2)	(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		1,973
Less than 12 months, Unrealized Loss		(48)
12 months or more, Estimated Fair Value		0
12 months or more, Unrealized Loss		0
Total Estimated Fair Value		1,973
Total Unrealized Loss		(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
Less than 12 months, Unrealized Loss		(34)
12 months or more, Estimated Fair Value		0
12 months or more, Unrealized Loss		0
Total Estimated Fair Value		2,836
Total Unrealized Loss		(34)
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		8,445
Less than 12 months, Unrealized Loss		(371)
12 months or more, Estimated Fair Value		0
12 months or more, Unrealized Loss		0
Total Estimated Fair Value		8,445
Total Unrealized Loss		$ (371)