Securities Held to Maturity (Summary of Amortized Cost, Unrealized Gains, Unrealized Losses and Estimated Fair Values) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	$ 99,457	$ 99,914
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	1,284	3,271
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	387	28
Debt Securities, Held-to-maturity, Fair Value	100,354	103,157
Tax Exempt State and Political Subdivisions General Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	72,842	73,179
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	1,056	2,524
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	194	0
Debt Securities, Held-to-maturity, Fair Value	73,704	75,703
Tax Exempt State and Political Subdivisions Water and Sewer Revenues [Member]
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	8,330	8,375
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	45	256
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	15	0
Debt Securities, Held-to-maturity, Fair Value	8,360	8,631
Tax Exempt State and Political Subdivisions Lease Revenues [Member]
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	4,376	4,395
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	0	88
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	27	0
Debt Securities, Held-to-maturity, Fair Value	4,349	4,483
Tax Exempt State and Political Subdivisions Sales Tax Revenues [Member]
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	4,632	4,649
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	20	94
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	45	3
Debt Securities, Held-to-maturity, Fair Value	4,607	4,740
Tax Exempt State and Political Subdivisions Other Revenues [Member]
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity	9,277	9,316
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	163	309
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	106	25
Debt Securities, Held-to-maturity, Fair Value	$ 9,334	$ 9,600