Securities Held to Maturity (Summary of Amortized Cost, Unrealized Gains, Unrealized Losses and Estimated Fair Values) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Marketable Securities [Line Items]
Debt Securities, Held-to-maturity	$ 91,600	$ 0
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	1,367
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	181
Debt Securities, Held-to-maturity, Fair Value	92,786
Tax Exempt State and Political Subdivisions General Obligations [Member]
Marketable Securities [Line Items]
Debt Securities, Held-to-maturity	69,731
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	1,081
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	37
Debt Securities, Held-to-maturity, Fair Value	70,775
Tax Exempt State and Political Subdivisions Water and Sewer Revenues [Member]
Marketable Securities [Line Items]
Debt Securities, Held-to-maturity	7,181
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	104
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	8
Debt Securities, Held-to-maturity, Fair Value	7,277
Tax Exempt State and Political Subdivisions Sales Tax Revenues [Member]
Marketable Securities [Line Items]
Debt Securities, Held-to-maturity	4,665
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	28
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	45
Debt Securities, Held-to-maturity, Fair Value	4,648
Tax Exempt State and Political Subdivisions Other Revenues [Member]
Marketable Securities [Line Items]
Debt Securities, Held-to-maturity	10,023
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	154
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	91
Debt Securities, Held-to-maturity, Fair Value	10,086
Tax Exempt Debt Securities [Member]
Marketable Securities [Line Items]
Debt Securities, Held-to-maturity	91,600
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	1,367
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	181
Debt Securities, Held-to-maturity, Fair Value	$ 92,786

Amount of investment in debt security measured at amortized cost (held-to-maturity).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121553693&loc=d3e26610-111562

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(6))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

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Amount of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity).

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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27232-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section S99
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-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Topic 320
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-Section 50
-Paragraph 5A
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