Securities (Summary Of Amortized Cost, Unrealized Gains, Unrealized Losses And Estimated Fair Values) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Total Amortized Cost	$ 284,419	$ 324,908
Available for sale securities, Unrealized Gains	2,257	5,329
Available for sale securities, Unrealized Losses	3,455	1,514
Available for sale securities, Estimated Fair Value	283,221	328,723	[1]
U S Government Corporations And Agencies Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Total Amortized Cost	28,830	31,260
Available for sale securities, Unrealized Gains	224	498
Available for sale securities, Unrealized Losses	372	145
Available for sale securities, Estimated Fair Value	28,682	31,613
Government Sponsored Agencies [Member]
Debt Securities, Available-for-sale [Line Items]
Total Amortized Cost	77,142	120,948
Available for sale securities, Unrealized Gains	662	1,276
Available for sale securities, Unrealized Losses	1,299	903
Available for sale securities, Estimated Fair Value	76,505	121,321
Nongovernment Sponsored Agencies [Member]
Debt Securities, Available-for-sale [Line Items]
Total Amortized Cost	820	2,045
Available for sale securities, Unrealized Gains	6	39
Available for sale securities, Unrealized Losses	5	7
Available for sale securities, Estimated Fair Value	821	2,077
State and Political Subdivisions General Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Total Amortized Cost	6,086	6,090
Available for sale securities, Unrealized Gains	0	0
Available for sale securities, Unrealized Losses	208	55
Available for sale securities, Estimated Fair Value	5,878	6,035
State and Policital Subdivisions Other Revenues [Member]
Debt Securities, Available-for-sale [Line Items]
Total Amortized Cost	13,468	11,657
Available for sale securities, Unrealized Gains	1	47
Available for sale securities, Unrealized Losses	372	62
Available for sale securities, Estimated Fair Value	13,097	11,642
Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Total Amortized Cost	10,893	16,375
Available for sale securities, Unrealized Gains	0	0
Available for sale securities, Unrealized Losses	168	130
Available for sale securities, Estimated Fair Value	10,725	16,245
Taxable Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Total Amortized Cost	137,239	188,375
Available for sale securities, Unrealized Gains	893	1,860
Available for sale securities, Unrealized Losses	2,424	1,302
Available for sale securities, Estimated Fair Value	135,708	188,933
Tax Exempt State and Political Subdivisions General Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Total Amortized Cost	74,920	65,560
Available for sale securities, Unrealized Gains	741	1,530
Available for sale securities, Unrealized Losses	512	198
Available for sale securities, Estimated Fair Value	75,149	66,892
Tax Exempt State and Political Subdivisions Water and Sewer Revenues [Member]
Debt Securities, Available-for-sale [Line Items]
Total Amortized Cost	21,858	23,108
Available for sale securities, Unrealized Gains	203	566
Available for sale securities, Unrealized Losses	105	3
Available for sale securities, Estimated Fair Value	21,956	23,671
Tax Exempt State and Political Subdivisions Lease Revenues [Member]
Debt Securities, Available-for-sale [Line Items]
Total Amortized Cost	12,366	13,024
Available for sale securities, Unrealized Gains	162	451
Available for sale securities, Unrealized Losses	4	2
Available for sale securities, Estimated Fair Value	12,524	13,473
Tax Exempt State and Political Subdivisions Electric Revenues [Member]
Debt Securities, Available-for-sale [Line Items]
Total Amortized Cost		6,205
Available for sale securities, Unrealized Gains		128
Available for sale securities, Unrealized Losses		0
Available for sale securities, Estimated Fair Value		6,333
Tax Exempt State and Political Subdivisions Sales Tax Revenues [Member]
Debt Securities, Available-for-sale [Line Items]
Total Amortized Cost	5,235	4,126
Available for sale securities, Unrealized Gains	32	140
Available for sale securities, Unrealized Losses	29	0
Available for sale securities, Estimated Fair Value	5,238	4,266
Tax Exempt State and Political Subdivisions University Revenues [Member]
Debt Securities, Available-for-sale [Line Items]
Total Amortized Cost		5,272
Available for sale securities, Unrealized Gains		38
Available for sale securities, Unrealized Losses		9
Available for sale securities, Estimated Fair Value		5,301
Tax Exempt State and Political Subdivisions Other Revenues [Member]
Debt Securities, Available-for-sale [Line Items]
Total Amortized Cost	32,664	19,101
Available for sale securities, Unrealized Gains	226	616
Available for sale securities, Unrealized Losses	381	0
Available for sale securities, Estimated Fair Value	32,509	19,717
Tax Exempt Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Total Amortized Cost	147,043	136,396
Available for sale securities, Unrealized Gains	1,364	3,469
Available for sale securities, Unrealized Losses	1,031	212
Available for sale securities, Estimated Fair Value	147,376	139,653
Equity Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Total Amortized Cost	137	137
Available for sale securities, Unrealized Gains	0	0
Available for sale securities, Unrealized Losses	0	0
Available for sale securities, Estimated Fair Value	$ 137	$ 137

[1] Derived from audited consolidated financial statements