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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 | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2013 Contract | Sep. 30, 2012 Contract | Sep. 30, 2013 Contract | Sep. 30, 2012 Contract
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |
Number of Contracts | 2 | 0 | 3 | 0
Recorded Investment | $ 14 | $ 0 | $ 18 | $ 0
Residential real estate [Member] |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |
Number of Contracts |  | 0 |  | 0
Recorded Investment | 9 | 0 | 9 | 0
Financing Receivable, Modification, Subsequent Default, Number of Contracts | 1 |  | 1 |
Loans to individuals [Member] |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |
Number of Contracts |  | 0 |  | 0
Recorded Investment | $ 5 | $ 0 | $ 9 | $ 0
Financing Receivable, Modification, Subsequent Default, Number of Contracts | 1 |  | 2 |

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- Definition Financing Receivable, Modification, Subsequent Default, Number of Contracts + References No definition available. + Details
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- Definition Financing Receivable, Modification, Subsequent Default, Recorded Investment + 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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- Definition Troubled debt restructuring number of contracts 90 days past due. + References No definition available. + Details
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Namespace Prefix: | fcf_
Data Type: | xbrli:integerItemType
Balance Type: | na
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