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Fair Values of Assets and Liabilities - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013
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Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Debt Securities | $ 1,308,399us-gaap_DebtInstrumentFairValue | $ 1,316,945us-gaap_DebtInstrumentFairValue
Estimated Fair Value of Available for Sale | 1,309,819us-gaap_AvailableForSaleSecurities | 1,318,365us-gaap_AvailableForSaleSecurities
Other investments | 44,545us-gaap_FederalHomeLoanBankStock | 35,444us-gaap_FederalHomeLoanBankStock
Loans Held for Sale | 2,502us-gaap_LoansHeldForSaleFairValueDisclosure | 0us-gaap_LoansHeldForSaleFairValueDisclosure
Other Assets | 11,186us-gaap_OtherAssetsFairValueDisclosure | 14,358us-gaap_OtherAssetsFairValueDisclosure
Total Assets | 1,368,052us-gaap_AssetsFairValueDisclosure | 1,368,167us-gaap_AssetsFairValueDisclosure
Other Liabilities | 10,671us-gaap_OtherLiabilitiesFairValueDisclosure | 14,318us-gaap_OtherLiabilitiesFairValueDisclosure
Total Liabilities | 10,671us-gaap_LiabilitiesFairValueDisclosure | 14,318us-gaap_LiabilitiesFairValueDisclosure
Equities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value of Available for Sale | 1,420us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesMember | 1,420us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesMember
US Government Agencies Debt Securities [Member] | Mortgage-Backed Securities-Residential [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Debt Securities | 25,936us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByAssetClassAxis = fcf_MortgageBackedSecuritiesResidentialMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember | 25,204us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByAssetClassAxis = fcf_MortgageBackedSecuritiesResidentialMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage-Backed Securities-Residential [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Debt Securities | 950,881us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByAssetClassAxis = fcf_MortgageBackedSecuritiesResidentialMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | 994,887us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByAssetClassAxis = fcf_MortgageBackedSecuritiesResidentialMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage-Backed Securities-Commercial [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Debt Securities | 74us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByAssetClassAxis = fcf_MortgageBackedSecuritiesCommercialMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | 105us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByAssetClassAxis = fcf_MortgageBackedSecuritiesCommercialMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Obligations of U.S. Government-Sponsored Enterprises [Member] | Other Government - Sponsored Enterprises [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Debt Securities | 267,877us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByAssetClassAxis = fcf_OtherGovernmentSponsoredEnterprisesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | 266,125us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByAssetClassAxis = fcf_OtherGovernmentSponsoredEnterprisesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Obligations of States and Political Subdivisions [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Debt Securities | 27,377us-gaap_DebtInstrumentFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = fcf_ObligationsOfStatesAndPoliticalSubdivisionsMember | 80us-gaap_DebtInstrumentFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = fcf_ObligationsOfStatesAndPoliticalSubdivisionsMember
Corporate Securities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Debt Securities | 7,255us-gaap_DebtInstrumentFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = fcf_CorporateSecuritiesMember | 7,021us-gaap_DebtInstrumentFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = fcf_CorporateSecuritiesMember
Pooled Trust Preferred Collateralized Debt Obligations [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Debt Securities | 28,999us-gaap_DebtInstrumentFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_TrustPreferredSecuritiesSubjectToMandatoryRedemptionMember | 23,523us-gaap_DebtInstrumentFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_TrustPreferredSecuritiesSubjectToMandatoryRedemptionMember
Level 1 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Debt Securities | 0us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member | 0us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
Estimated Fair Value of Available for Sale | 0us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member | 0us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
Other investments | 0us-gaap_FederalHomeLoanBankStock / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member | 0us-gaap_FederalHomeLoanBankStock / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
Loans Held for Sale | 0us-gaap_LoansHeldForSaleFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member | 0us-gaap_LoansHeldForSaleFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
Other Assets | 0us-gaap_OtherAssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member | 0us-gaap_OtherAssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
Total Assets | 0us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member | 0us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
Other Liabilities | 0us-gaap_OtherLiabilitiesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member | 0us-gaap_OtherLiabilitiesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
Total Liabilities | 0us-gaap_LiabilitiesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member | 0us-gaap_LiabilitiesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
Level 1 [Member] | Equities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value of Available for Sale | 0us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member | 0us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
Level 1 [Member] | US Government Agencies Debt Securities [Member] | Mortgage-Backed Securities-Residential [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Debt Securities | 0us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByAssetClassAxis = fcf_MortgageBackedSecuritiesResidentialMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember | 0us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByAssetClassAxis = fcf_MortgageBackedSecuritiesResidentialMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Level 1 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage-Backed Securities-Residential [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Debt Securities | 0us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByAssetClassAxis = fcf_MortgageBackedSecuritiesResidentialMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | 0us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByAssetClassAxis = fcf_MortgageBackedSecuritiesResidentialMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Level 1 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage-Backed Securities-Commercial [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Debt Securities | 0us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByAssetClassAxis = fcf_MortgageBackedSecuritiesCommercialMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | 0us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByAssetClassAxis = fcf_MortgageBackedSecuritiesCommercialMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Level 1 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Other Government - Sponsored Enterprises [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Debt Securities | 0us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByAssetClassAxis = fcf_OtherGovernmentSponsoredEnterprisesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | 0us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByAssetClassAxis = fcf_OtherGovernmentSponsoredEnterprisesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Level 1 [Member] | Obligations of States and Political Subdivisions [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Debt Securities | 0us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = fcf_ObligationsOfStatesAndPoliticalSubdivisionsMember | 0us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = fcf_ObligationsOfStatesAndPoliticalSubdivisionsMember
Level 1 [Member] | Corporate Securities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Debt Securities | 0us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = fcf_CorporateSecuritiesMember | 0us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = fcf_CorporateSecuritiesMember
Level 1 [Member] | Pooled Trust Preferred Collateralized Debt Obligations [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Debt Securities | 0us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_TrustPreferredSecuritiesSubjectToMandatoryRedemptionMember | 0us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_TrustPreferredSecuritiesSubjectToMandatoryRedemptionMember
Level 2 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Debt Securities | 1,279,400us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | 1,293,422us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
Estimated Fair Value of Available for Sale | 1,279,400us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | 1,293,422us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
Other investments | 44,545us-gaap_FederalHomeLoanBankStock / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | 35,444us-gaap_FederalHomeLoanBankStock / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
Loans Held for Sale | 2,502us-gaap_LoansHeldForSaleFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | 0us-gaap_LoansHeldForSaleFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
Other Assets | 11,186us-gaap_OtherAssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | 14,358us-gaap_OtherAssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
Total Assets | 1,337,633us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | 1,343,224us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
Other Liabilities | 10,671us-gaap_OtherLiabilitiesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | 14,318us-gaap_OtherLiabilitiesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
Total Liabilities | 10,671us-gaap_LiabilitiesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | 14,318us-gaap_LiabilitiesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
Level 2 [Member] | Equities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value of Available for Sale | 0us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | 0us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
Level 2 [Member] | US Government Agencies Debt Securities [Member] | Mortgage-Backed Securities-Residential [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Debt Securities | 25,936us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByAssetClassAxis = fcf_MortgageBackedSecuritiesResidentialMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember | 25,204us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByAssetClassAxis = fcf_MortgageBackedSecuritiesResidentialMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Level 2 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage-Backed Securities-Residential [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Debt Securities | 950,881us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByAssetClassAxis = fcf_MortgageBackedSecuritiesResidentialMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | 994,887us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByAssetClassAxis = fcf_MortgageBackedSecuritiesResidentialMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Level 2 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage-Backed Securities-Commercial [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Debt Securities | 74us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByAssetClassAxis = fcf_MortgageBackedSecuritiesCommercialMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | 105us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByAssetClassAxis = fcf_MortgageBackedSecuritiesCommercialMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Level 2 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Other Government - Sponsored Enterprises [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Debt Securities | 267,877us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByAssetClassAxis = fcf_OtherGovernmentSponsoredEnterprisesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | 266,125us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByAssetClassAxis = fcf_OtherGovernmentSponsoredEnterprisesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Level 2 [Member] | Obligations of States and Political Subdivisions [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Debt Securities | 27,377us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = fcf_ObligationsOfStatesAndPoliticalSubdivisionsMember | 80us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = fcf_ObligationsOfStatesAndPoliticalSubdivisionsMember
Level 2 [Member] | Corporate Securities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Debt Securities | 7,255us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = fcf_CorporateSecuritiesMember | 7,021us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = fcf_CorporateSecuritiesMember
Level 2 [Member] | Pooled Trust Preferred Collateralized Debt Obligations [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Debt Securities | 0us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_TrustPreferredSecuritiesSubjectToMandatoryRedemptionMember | 0us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_TrustPreferredSecuritiesSubjectToMandatoryRedemptionMember
Level 3 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Debt Securities | 28,999us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member | 23,523us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member
Estimated Fair Value of Available for Sale | 30,419us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member | 24,943us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member
Other investments | 0us-gaap_FederalHomeLoanBankStock / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member | 0us-gaap_FederalHomeLoanBankStock / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member
Loans Held for Sale | 0us-gaap_LoansHeldForSaleFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member | 0us-gaap_LoansHeldForSaleFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member
Other Assets |  | 0us-gaap_OtherAssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member
Total Assets | 30,419us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member | 24,943us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member
Other Liabilities | 0us-gaap_OtherLiabilitiesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member | 0us-gaap_OtherLiabilitiesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member
Total Liabilities | 0us-gaap_LiabilitiesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member | 0us-gaap_LiabilitiesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member
Level 3 [Member] | Equities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value of Available for Sale |  | 1,420us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member
Level 3 [Member] | US Government Agencies Debt Securities [Member] | Mortgage-Backed Securities-Residential [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Debt Securities | 0us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByAssetClassAxis = fcf_MortgageBackedSecuritiesResidentialMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember | 0us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByAssetClassAxis = fcf_MortgageBackedSecuritiesResidentialMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Level 3 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage-Backed Securities-Residential [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Debt Securities | 0us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByAssetClassAxis = fcf_MortgageBackedSecuritiesResidentialMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | 0us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByAssetClassAxis = fcf_MortgageBackedSecuritiesResidentialMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Level 3 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage-Backed Securities-Commercial [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Debt Securities | 0us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByAssetClassAxis = fcf_MortgageBackedSecuritiesCommercialMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | 0us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByAssetClassAxis = fcf_MortgageBackedSecuritiesCommercialMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Level 3 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Other Government - Sponsored Enterprises [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Debt Securities | 0us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByAssetClassAxis = fcf_OtherGovernmentSponsoredEnterprisesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | 0us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByAssetClassAxis = fcf_OtherGovernmentSponsoredEnterprisesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Level 3 [Member] | Obligations of States and Political Subdivisions [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Debt Securities | 0us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = fcf_ObligationsOfStatesAndPoliticalSubdivisionsMember | 0us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = fcf_ObligationsOfStatesAndPoliticalSubdivisionsMember
Level 3 [Member] | Corporate Securities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Debt Securities | 0us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = fcf_CorporateSecuritiesMember | 0us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = fcf_CorporateSecuritiesMember
Level 3 [Member] | Pooled Trust Preferred Collateralized Debt Obligations [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total Debt Securities | $ 28,999us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_TrustPreferredSecuritiesSubjectToMandatoryRedemptionMember | $ 23,523us-gaap_DebtInstrumentFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_TrustPreferredSecuritiesSubjectToMandatoryRedemptionMember

X
- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
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- Definition Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562 + Details
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- Definition Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13433-108611 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13476-108611 + Details
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- Definition Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 325 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6478792&loc=d3e63345-112809 + Details
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- Definition Fair value of financial and nonfinancial obligations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
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- Definition Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables. + References No definition available. + Details
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- Definition Fair value portion of other assets. + References No definition available. + Details
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- Definition Fair value portion of other liabilities. + References No definition available. + Details
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