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Derivatives - Schedule of Change in Fair Value of Derivative Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010
Derivative [Line Items] |  |  |
Increase (decrease) in other income | $ 755 | $ (6,687) | $ 141

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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