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Derivatives - Additional Information (Detail) (USD $) | Sep. 30, 2014
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Risk participation Agreements [Line Items] |
HedgedItemsOfCashFlowHedge | $ 100,000,000
Risk Participation Agreements Purchased [Domain] |
Risk participation Agreements [Line Items] |
Number of interest rate swaps | 13
Risk Participation Agreements Sold [Domain] |
Risk participation Agreements [Line Items] |
Number of interest rate swaps | 4
InterestRateSwapThreeYearLife [Member] |
Risk participation Agreements [Line Items] |
Derivative, Notional Amount | 50,000,000
InterestRateSwapFourYearLife [Member] [Member] |
Risk participation Agreements [Line Items] |
Derivative, Notional Amount | $ 50,000,000

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- Definition HedgedItemsOfCashFlowHedge + References No definition available. + Details
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Balance Type: | debit
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- Details
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Namespace Prefix: | fcf_
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Period Type: | duration

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- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
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Namespace Prefix: | invest_
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Balance Type: | na
Period Type: | instant

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- Definition Number of credit risk derivative instruments held. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1B -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5580258-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1A -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5579245-113959 + Details
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