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Fair Value of Financial Instruments (Fair Value By Balance Sheet Grouping) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held for sale	$ 443	$ 0
Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	48,343	72,720
Interest bearing deposits in banks	1,410	1,595
Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities - AFS	82,460	110,018
Investment securities - HTM	182,510	182,380
Financial derivatives	778	1,068
Accrued interest receivable	828	933
Deposits - non-maturity	1,355,444	1,450,210
Deposits - time deposits	193,337	120,083
Short-term borrowed funds	45,418	64,565
Long-term borrowed funds	110,809	30,909
Accrued interest payable	612	151
Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities - AFS	14,709	15,871
Investment securities - HTM	1,905	20,700
Loans, net	1,319,456	1,177,702
Accrued interest receivable	6,659	5,118
Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	48,343	72,720
Interest bearing deposits in banks	1,410	1,595
Investment securities - AFS	97,169	125,889
Investment securities - HTM	214,297	235,659
Restricted bank Stock	5,250	1,027
Loans, net	1,388,847	1,264,684
Financial derivatives	778	1,068
Accrued interest receivable	7,487	6,051
Deposits - non-maturity	1,355,444	1,450,210
Deposits - time deposits	195,533	120,523
Short-term borrowed funds	45,418	64,565
Long-term borrowed funds	110,929	30,929
Accrued interest payable	612	151
Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	48,343	72,720
Interest bearing deposits in banks	1,410	1,595
Investment securities - AFS	97,169	125,889
Investment securities - HTM	184,415	203,080
Loans, net	1,319,456	1,177,702
Financial derivatives	778	1,068
Accrued interest receivable	7,487	6,051
Deposits - non-maturity	1,355,444	1,450,210
Deposits - time deposits	193,337	120,083
Short-term borrowed funds	45,418	64,565
Long-term borrowed funds	110,809	30,909
Accrued interest payable	$ 612	$ 151

X

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. Includes disclosure of claims held for interest amounts due a company.

+ References

No definition available.

+ Details

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Namespace Prefix:	func_
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Balance Type:	debit
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X

- Definition

Available For Sale Securities Fair Value

+ References

No definition available.

+ Details

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X

- Definition

Held To Maturity Securities Fair Value Disclosure

+ References

No definition available.

+ Details

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- Definition

For banks and other depository institutions (including Federal Reserve Banks, if applicable): The fair value of Interest-bearing deposits in other financial institutions for relatively short periods of time including, for example, certificates of deposits.

+ References

No definition available.

+ Details

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- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. Includes deposit liabilities having no set maturity (excluding time deposits)

+ References

No definition available.

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X

- Definition

Information on investments in correspondent bank stock

+ References

No definition available.

+ Details

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X

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure. This item represents the aggregate of all time deposit liabilities held by the entity, including foreign and domestic, interest and noninterest bearing.

+ References

No definition available.

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X

- Definition

Fair value portion of accrued expenses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.20)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

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- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Fair value as of the balance sheet date of all interest rate derivative assets designated as cash flow hedging instruments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (c)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480434/815-10-50-4B

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- Definition

Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

+ References

No definition available.

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- Definition

Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Publisher FASB
-URI https://asc.fasb.org//310-10/tableOfContent

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X

- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

+ Details

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- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents the amount of short-term debt existing as of the balance sheet date.

+ References

No definition available.

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