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Derivatives - Schedule of Changes in Fair Value of Derivative Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified | 3 Months Ended
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Mar. 31, 2015 | Mar. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract] |  |
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net | $ (230)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet | $ (58)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
Derivative Instruments Designated As Hedging Instruments Interest Income | 381 fcf_DerivativeInstrumentsDesignatedAsHedgingInstrumentsInterestIncome | 0 fcf_DerivativeInstrumentsDesignatedAsHedgingInstrumentsInterestIncome
Derivative, Net Hedge Ineffectiveness Gain (Loss) | $ 9 us-gaap_DerivativeNetHedgeIneffectivenessGainLoss | $ 0 us-gaap_DerivativeNetHedgeIneffectivenessGainLoss

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- Definition Derivative Instruments Designated As Hedging Instruments Interest Income + References No definition available. + Details
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- Details
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- Definition Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624171-113959 + Details
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- Definition Amount of gain (loss) from the ineffectiveness of the hedge. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624171-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 25 -Section 50 -Paragraph 1 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6886632&loc=d3e76258-113986 + Details
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