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Investment Securities - Proceeds from Sale, Gross Gains (Losses) Realized on Sales, Maturities and Other-Than-Temporary Impairment Charges Related to Securities Available for Sale (Detail) (USD $) In Thousands, unless otherwise specified | 3 Months Ended
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Mar. 31, 2015 | Mar. 31, 2014
Investments, Debt and Equity Securities [Abstract] |  |
Proceeds from sales | $ 0 us-gaap_ProceedsFromSaleOfAvailableForSaleSecurities | $ 0 us-gaap_ProceedsFromSaleOfAvailableForSaleSecurities
Sales Transactions: |  |
Gross gains | 0 us-gaap_AvailableForSaleSecuritiesGrossRealizedGains | 0 us-gaap_AvailableForSaleSecuritiesGrossRealizedGains
Gross losses | 0 us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses | 0 us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments | 0 us-gaap_AvailableforsaleSecuritiesGrossRealizedGainLossExcludingOtherThanTemporaryImpairments | 0 us-gaap_AvailableforsaleSecuritiesGrossRealizedGainLossExcludingOtherThanTemporaryImpairments
Maturities and impairment |  |
Gross Gains | 105 fcf_GrossGains | 0 fcf_GrossGains
Gross Losses | 0 fcf_GrossLosses | 0 fcf_GrossLosses
Other Than Temporary Impairment | 0 fcf_OtherThanTemporaryImpairment | 0 fcf_OtherThanTemporaryImpairment
Gain Losses Maturities And Impairment | 105 fcf_GainLossesMaturitiesAndImpairment | 0 fcf_GainLossesMaturitiesAndImpairment
Net gains and impairment | $ 105 fcf_NetGainsAndImpairment | $ 0 fcf_NetGainsAndImpairment

X
- Definition Gain losses maturities and impairment. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition This item represents the gross gain on maturities of available for sale securities. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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- Definition This item represents the gross loss on maturities of available for sale securities. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
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- Details
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Period Type: | duration

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- Definition Net gains and impairment. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Other-than-temporary impairment. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=49167202&loc=d3e26805-111562 + Details
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- Definition This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563 + Details
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- Definition This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563 + Details
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- Definition The cash inflow associated with the sale of debt and equity securities classified as available-for-sale securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Investing Activities -URI http://asc.fasb.org/extlink&oid=6516133 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=49167202&loc=d3e26853-111562 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 12 -Subparagraph (a),(b) -URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3179-108585 + Details
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