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v3.19.1

Consolidated Statement of Income (Parenthetical) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2017 USD ($)
Consolidated Statements of Income [Abstract] |
Provision for income tax expense, tax reform impact | $ 3,226

X
- Definition Amount of reasonable estimate for income tax expense (benefit) from effect of Tax Cuts and Jobs Act of 2017 for which accounting for tax effect is incomplete. + References No definition available. + Details
Name: | func_TaxCutsAndJobsActOf2017IncomeTaxExpenseBenefitIncompleteAccountingProvisionalAmount
Namespace Prefix: | func_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_IncomeStatementAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration