Securities (Summary Of Amortized Cost, Unrealized Gains, Unrealized Losses And Estimated Fair Values) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	$ 324,908	$ 267,105
Available for sale securities, Unrealized Gains	5,329	3,005
Available for sale securities, Unrealized Losses	1,514	3,568
Available for sale securities, Estimated Fair Value	328,723	266,542
Tax Exempt State and Political Subdivisions Electric Revenues [Member]
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	6,205	3,247
Available for sale securities, Unrealized Gains	128	10
Available for sale securities, Unrealized Losses	0	48
Available for sale securities, Estimated Fair Value	6,333	3,209
Tax Exempt State and Political Subdivisions Sales Tax Revenues [Member]
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	4,126	2,870
Available for sale securities, Unrealized Gains	140	0
Available for sale securities, Unrealized Losses	0	34
Available for sale securities, Estimated Fair Value	4,266	2,836
U.S. Government and agencies and corporations [Member]
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	31,260	14,580
Available for sale securities, Unrealized Gains	498	642
Available for sale securities, Unrealized Losses	145	48
Available for sale securities, Estimated Fair Value	31,613	15,174
Government-sponsored agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	120,948	138,451
Available for sale securities, Unrealized Gains	1,276	1,554
Available for sale securities, Unrealized Losses	903	1,159
Available for sale securities, Estimated Fair Value	121,321	138,846
Nongovernment-sponsored entities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	2,045	4,631
Available for sale securities, Unrealized Gains	39	44
Available for sale securities, Unrealized Losses	7	22
Available for sale securities, Estimated Fair Value	2,077	4,653
State and Political Subdivisions General Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	6,090
Available for sale securities, Unrealized Gains	0
Available for sale securities, Unrealized Losses	55
Available for sale securities, Estimated Fair Value	6,035
State and policital subdivisions, Other revenues [Member]
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	11,657
Available for sale securities, Unrealized Gains	47
Available for sale securities, Unrealized Losses	62
Available for sale securities, Estimated Fair Value	11,642
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	16,375	18,295
Available for sale securities, Unrealized Gains	0	23
Available for sale securities, Unrealized Losses	130	148
Available for sale securities, Estimated Fair Value	16,245	18,170
Total taxable debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	188,375	175,957
Available for sale securities, Unrealized Gains	1,860	2,263
Available for sale securities, Unrealized Losses	1,302	1,377
Available for sale securities, Estimated Fair Value	188,933	176,843
Tax Exempt State and Political Subdivisions General Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	65,560	49,449
Available for sale securities, Unrealized Gains	1,530	569
Available for sale securities, Unrealized Losses	198	1,388
Available for sale securities, Estimated Fair Value	66,892	48,630
Tax Exempt State and Political Subdivisions Water and Sewer Revenues [Member]
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	23,108	9,087
Available for sale securities, Unrealized Gains	566	63
Available for sale securities, Unrealized Losses	3	149
Available for sale securities, Estimated Fair Value	23,671	9,001
Tax Exempt State and Political Subdivisions Lease Revenues [Member]
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	13,024	9,037
Available for sale securities, Unrealized Gains	451	7
Available for sale securities, Unrealized Losses	2	201
Available for sale securities, Estimated Fair Value	13,473	8,843
Tax Exempt State and Political Subdivisions University Revenues [Member]
Schedule of Available-for-sale Securities [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]
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	19,101	17,321
Available for sale securities, Unrealized Gains	616	93
Available for sale securities, Unrealized Losses	0	371
Available for sale securities, Estimated Fair Value	19,717	17,043
Total tax-exempt debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	136,396	91,011
Available for sale securities, Unrealized Gains	3,469	742
Available for sale securities, Unrealized Losses	212	2,191
Available for sale securities, Estimated Fair Value	139,653	89,562
Equity securities [Member]
Schedule of Available-for-sale Securities [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