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Commitments and Contingent Liabilities - Notional Amount of Outstanding Commitments (Detail) (USD $) In Thousands, unless otherwise specified | Sep. 30, 2012 | Dec. 31, 2011
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Commitments to extend credit [Member] |  |
Contingencies And Commitments [Line Items] |  |
Financial instrument of credit risk | $ 1,515,221 | $ 1,495,009
Financial standby letters of credit [Member] |  |
Contingencies And Commitments [Line Items] |  |
Financial instrument of credit risk | 48,864 | 53,689
Performance standby letters of credit [Member] |  |
Contingencies And Commitments [Line Items] |  |
Financial instrument of credit risk | 77,795 | 76,371
Commercial letters of credit [Member] |  |
Contingencies And Commitments [Line Items] |  |
Financial instrument of credit risk | $ 1,047 | $ 1,297

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

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- Definition Notional amount of outstanding commitments and letters of credit. + References No definition available. + Details
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Namespace Prefix: | fcf_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant