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Derivatives - Schedule of Changes in Fair Value of Derivative Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2012 | Sep. 30, 2011 | Sep. 30, 2012 | Sep. 30, 2011
Derivative [Line Items] |  |  |  |
Increase (decrease) in other income | $ 375 | $ (5,108) | $ 1,126 | $ (5,643)

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- Definition Change in the fair value of derivative assets and derivative liabilities attributable to credit risk included in other income. + References No definition available. + Details
Name: | fcf_ChangeInOtherIncomeDueToCreditRiskOnInterestRateSwaps
Namespace Prefix: | fcf_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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