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.

No definition available.

+ Details

Name:	us-gaap_FinancingReceivableImpairedLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953676-111524

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after troubled debt restructuring, of modified financing receivable.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=func_TroubledDebtRestructuringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=func_ExtensionOfMaturityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=func_CommercialRealEstateNonOwnerOccupiedFinancingReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Loans And Related Allowances For Loan Losses (TDRs) (Details) $ in Thousands	3 Months Ended	6 Months Ended		12 Months Ended
	Jun. 30, 2021 USD ($) contract	Jun. 30, 2022 contract	Jun. 30, 2021 USD ($) contract	Dec. 31, 2021 contract
Troubled Debt Restructuring [Member]
Financing Receivable, Impaired [Line Items]
Number of contracts		12		12
Extension Of Maturity [Member]
Financing Receivable, Impaired [Line Items]
Number of contracts	1		1
Recorded Investment \| $	$ 109		$ 109
Commercial real estate- non owner-occupied [Member] \| Extension Of Maturity [Member]
Financing Receivable, Impaired [Line Items]
Number of contracts	1		1
Recorded Investment \| $	$ 109		$ 109