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v2.4.1.9

Commitments and Letters of Credit - Additional Information (Detail) (USD $) | Dec. 31, 2014 | Dec. 31, 2013
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Loss Contingencies [Line Items] |  |
Notional amount of financial standby letters of credit | $ 300,000fcf_NotionalAmountOfFinancialStandbyLettersOfCredit |
Notional amount of performance standby letters of credit | 1,900,000fcf_NotionalAmountOfPerformanceStandbyLettersOfCredit |
Notional amount of commercial letters of credit | 232,000fcf_NotionalAmountOfCommercialLettersOfCredit |
Financial instrument of credit risk | 200,000us-gaap_FairValueConcentrationOfRiskCommitments | 100,000us-gaap_FairValueConcentrationOfRiskCommitments
Unused commitments and letters of credit [Member] |  |
Loss Contingencies [Line Items] |  |
Commitment liability | $ 3,100,000fcf_ReserveForOffBalanceSheetActivities / us-gaap_FinancialInstrumentAxis = fcf_UnusedCommitmentsAndLettersOfCreditMember | $ 3,200,000fcf_ReserveForOffBalanceSheetActivities / us-gaap_FinancialInstrumentAxis = fcf_UnusedCommitmentsAndLettersOfCreditMember

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

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- Definition Notional Amount Of Financial Standby Letters Of Credit + References No definition available. + Details
Name: | fcf_NotionalAmountOfFinancialStandbyLettersOfCredit
Namespace Prefix: | fcf_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Notional amount of performance standby letters of credit. + References No definition available. + Details
Name: | fcf_NotionalAmountOfPerformanceStandbyLettersOfCredit
Namespace Prefix: | fcf_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Reserve for credit risk of off-balance sheet activities + References No definition available. + Details
Name: | fcf_ReserveForOffBalanceSheetActivities
Namespace Prefix: | fcf_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition This item represents disclosure of all significant concentrations of credit risk or market risk arising from the subject financial instrument (as defined), whether from an individual counterparty or groups of counterparties. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.25) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 25 -Article 5 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 19 -Article 7 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 17 -Article 9 + Details
Name: | us-gaap_FairValueConcentrationOfRiskCommitments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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

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- Details
Name: | us-gaap_FinancialInstrumentAxis=fcf_UnusedCommitmentsAndLettersOfCreditMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |