Name:	func_DebtInstrumentIssuancePeriod
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Date when the debt instrument is scheduled to be fully repaid, which may be presented in a variety of ways (year, month and year, day, month and year, quarter, etc)

No definition available.

Name:	func_DebtInstrumentMaturityPeriod
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Debt Instrument Redemption After First Issuance

No definition available.

Name:	func_DebtInstrumentRedemptionAfterFirstIssuance
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Maximum Allowable Period Of Interest Deferment

No definition available.

Name:	func_MaximumAllowablePeriodOfInterestDeferment
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Aggregate par or stated value of issued nonredeemable common stock (or common stock redeemable solely at the option of the issuer). This item includes treasury stock repurchased by the entity. Note: elements for number of nonredeemable common shares, par value and other disclosure concepts are in another section within stockholders' equity.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

No definition available.

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
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-Section 50
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Including the current and noncurrent portions, the carrying value of junior subordinated long-term debt owed to unconsolidated subsidiary trusts as of the balance sheet date. Such debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets and was initially scheduled to be repaid after one year or beyond the normal operating cycle if longer.

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Value of all nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) held by shareholders, which is net of related treasury stock. May be all or a portion of the number of preferred shares authorized. These shares represent the ownership interest of the preferred shareholders.

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Name:	us-gaap_PreferredStockValueOutstanding
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Name:	srt_ConsolidatedEntitiesAxis=func_FirstUnitedStatutoryTrustOneAndTwoMember
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