Commercial amount benchmark minimum criticized relationships for annual review by independent reviewer.

No definition available.

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Period Type:	duration

- Definition

Commerical amount benchmark minimum for internal annual review.

+ References

No definition available.

+ Details

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Namespace Prefix:	func_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Commerical amount benchmark minimum for annual review by independent reviewer.

+ References

No definition available.

+ Details

Name:	func_CommericalAmountBenchmarkMinimumForAnnualReviewByIndependentReviewer
Namespace Prefix:	func_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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- Details

Name:	us-gaap_FinancingReceivableModificationsLineItems
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/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 33

-URI http://asc.fasb.org/extlink&oid=28368275&loc=SL6953676-111524

+ Details

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Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of financing receivables that have been modified by troubled debt restructurings within the previous 12 months and for which there was a payment default.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 34

-URI http://asc.fasb.org/extlink&oid=28368275&loc=SL6953682-111524

+ Details

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Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of investment related to financing receivables modified by troubled debt restructurings within the previous 12 months, for which there was a payment default.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=28368275&loc=d3e5111-111524

+ Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Reflects the amount of the write-down related to a troubled debt restructuring.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 40

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=25495931&loc=d3e18845-111554

+ Details

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

Loans and Related Allowance for Loan Losses (Narrative) (Details) (USD $)	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Financing Receivable, Modifications [Line Items]
Commercial amount benchmark minimum for internal annual review	$ 500,000
Commercial amount benchmark minimum for annual review by independent reviewer	750,000
Commercial amount benchmark minimum criticized relationships for annual review by independent reviewer	500,000
Nonaccrual loans subject to partial charge off	13,913,000		17,396,000
Reduction of the ALL resulting from new TDRs	1,055	11,266
Partial Charge Off [Member]
Financing Receivable, Modifications [Line Items]
Nonaccrual loans subject to partial charge off	4,900,000		1,900,000
New TDR [Member]
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	2	3
Pre Existing TDR [Member]
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	5	4
Acquisition and Development (A&D) TDR [Member]
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, number of contracts	3
Financing receivable, modifications, subsequent default, recorded investment	1,700,000
Commerical Real Estate TDR [Member]
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, subsequent default, recorded investment	400,000
Commerical and Industrial TDR [Member]
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, subsequent default, recorded investment	200,000
Commercial Real Estate- Non Owner-Occupied [Member]
Financing Receivable, Modifications [Line Items]
Nonaccrual loans subject to partial charge off	794,000		681,000
Financing receivable, modifications, subsequent default, number of contracts		3
Financing receivable, modifications, subsequent default, recorded investment		2,200,000
Acquisition and Development [Member]
Financing Receivable, Modifications [Line Items]
Financing receivable, modifications, subsequent default, number of contracts		2
Financing receivable, modifications, subsequent default, recorded investment		$ 400,000