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Loans and Allowance for Credit Losses - Troubled Debt Restructuring is 90 Days or More Past Due (Detail) (USD $) In Thousands, unless otherwise specified | 9 Months Ended
--- | ---
Sep. 30, 2012 Contract | Sep. 30, 2011 Contract
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Troubled debt restructuring number of contracts 90 days past due | 0 | 1
Troubled debt restructuring recorded investment 90 days past due | $ 0 | $ 88
Real estate construction [Member] |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Troubled debt restructuring number of contracts 90 days past due | 0 | 1
Troubled debt restructuring recorded investment 90 days past due | $ 0 | $ 88

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- Definition Troubled debt restructuring number of contracts 90 days past due. + References No definition available. + Details
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- Definition Troubled debt restructuring recorded investment ninety days past due. + References No definition available. + Details
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Namespace Prefix: | fcf_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration