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Loans and Allowance for Credit Losses - Allowance for Credit Losses (Detail) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Financing Receivable, Allowance for Credit Losses [Roll Forward] |  |  |
Beginning Balance | $ 54,225us-gaap_FinancingReceivableAllowanceForCreditLosses | $ 67,187us-gaap_FinancingReceivableAllowanceForCreditLosses | $ 61,234us-gaap_FinancingReceivableAllowanceForCreditLosses
Charge-offs | (17,472)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs | (35,178)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs | (16,969)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
Recoveries | 4,102us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery | 2,989us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery | 2,378us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
Provision for credit losses | 11,196us-gaap_ProvisionForLoanAndLeaseLosses | 19,227us-gaap_ProvisionForLoanAndLeaseLosses | 20,544us-gaap_ProvisionForLoanAndLeaseLosses
Ending Balance | 52,051us-gaap_FinancingReceivableAllowanceForCreditLosses | 54,225us-gaap_FinancingReceivableAllowanceForCreditLosses | 67,187us-gaap_FinancingReceivableAllowanceForCreditLosses
Ending balance: individually evaluated for impaired | 9,461us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 | 8,824us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 | 17,778us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
Ending balance: collectively evaluated for impaired | 42,590us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment | 45,401us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment | 49,409us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
Ending balance | 4,457,308us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome | 4,283,833us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome | 4,204,704us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
Ending balance: individually evaluated for impaired | 48,442us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment | 52,595us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment | 100,187us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
Ending balance: collectively evaluated for impaired | 4,408,866us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment | 4,231,238us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment | 4,104,517us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
Commercial, financial, agricultural and other [Member] |  |  |
Financing Receivable, Allowance for Credit Losses [Roll Forward] |  |  |
Beginning Balance | 22,663us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherMember | 19,852us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherMember | 18,200us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherMember
Charge-offs | (8,911)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherMember | (18,399)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherMember | (5,207)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherMember
Recoveries | 734us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherMember | 455us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherMember | 443us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherMember
Provision for credit losses | 15,141us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherMember | 20,755us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherMember | 6,416us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherMember
Ending Balance | 29,627us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherMember | 22,663us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherMember | 19,852us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherMember
Ending balance: individually evaluated for impaired | 9,304us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherMember | 7,364us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherMember | 10,331us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherMember
Ending balance: collectively evaluated for impaired | 20,323us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherMember | 15,299us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherMember | 9,521us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherMember
Ending balance | 1,052,109us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherMember | 1,021,056us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherMember | 1,019,822us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherMember
Ending balance: individually evaluated for impaired | 33,332us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherMember | 27,251us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherMember | 33,443us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherMember
Ending balance: collectively evaluated for impaired | 1,018,777us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherMember | 993,805us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherMember | 986,379us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherMember
Real estate construction [Member] |  |  |
Financing Receivable, Allowance for Credit Losses [Roll Forward] |  |  |
Beginning Balance | 6,600us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionMember | 8,928us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionMember | 6,756us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionMember
Charge-offs | (296)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionMember | (773)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionMember | (3,601)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionMember
Recoveries | 1,340us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionMember | 501us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionMember | 582us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionMember
Provision for credit losses | (5,581)us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionMember | (2,056)us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionMember | 5,191us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionMember
Ending Balance | 2,063us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionMember | 6,600us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionMember | 8,928us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionMember
Ending balance: individually evaluated for impaired | 0us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionMember | 94us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionMember | 300us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionMember
Ending balance: collectively evaluated for impaired | 2,063us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionMember | 6,506us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionMember | 8,628us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionMember
Ending balance | 120,785us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionMember | 93,289us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionMember | 87,438us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionMember
Ending balance: individually evaluated for impaired | 193us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionMember | 3,844us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionMember | 11,177us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionMember
Ending balance: collectively evaluated for impaired | 120,592us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionMember | 89,445us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionMember | 76,261us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionMember
Residential real estate [Member] |  |  |
Financing Receivable, Allowance for Credit Losses [Roll Forward] |  |  |
Beginning Balance | 7,727us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialRealEstateMember | 5,908us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialRealEstateMember | 8,237us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialRealEstateMember
Charge-offs | (3,153)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialRealEstateMember | (1,814)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialRealEstateMember | (3,828)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialRealEstateMember
Recoveries | 650us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialRealEstateMember | 1,264us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialRealEstateMember | 422us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialRealEstateMember
Provision for credit losses | (1,560)us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialRealEstateMember | 2,369us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialRealEstateMember | 1,077us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialRealEstateMember
Ending Balance | 3,664us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialRealEstateMember | 7,727us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialRealEstateMember | 5,908us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialRealEstateMember
Ending balance: individually evaluated for impaired | 56us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialRealEstateMember | 1,282us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialRealEstateMember | 780us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialRealEstateMember
Ending balance: collectively evaluated for impaired | 3,608us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialRealEstateMember | 6,445us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialRealEstateMember | 5,128us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialRealEstateMember
Ending balance | 1,226,344us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialRealEstateMember | 1,262,718us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialRealEstateMember | 1,241,565us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialRealEstateMember
Ending balance: individually evaluated for impaired | 7,127us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialRealEstateMember | 9,349us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialRealEstateMember | 6,444us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialRealEstateMember
Ending balance: collectively evaluated for impaired | 1,219,217us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialRealEstateMember | 1,253,369us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialRealEstateMember | 1,235,121us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialRealEstateMember
Commercial real estate [Member] |  |  |
Financing Receivable, Allowance for Credit Losses [Roll Forward] |  |  |
Beginning Balance | 11,778us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember | 22,441us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember | 18,961us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember
Charge-offs | (1,148)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember | (10,513)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember | (851)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember
Recoveries | 612us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember | 136us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember | 410us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember
Provision for credit losses | 639us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember | (286)us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember | 3,921us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember
Ending Balance | 11,881us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember | 11,778us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember | 22,441us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember
Ending balance: individually evaluated for impaired | 101us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember | 84us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember | 6,367us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember
Ending balance: collectively evaluated for impaired | 11,780us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember | 11,694us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember | 16,074us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember
Ending balance | 1,405,256us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember | 1,296,472us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember | 1,273,661us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember
Ending balance: individually evaluated for impaired | 7,790us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember | 12,151us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember | 49,123us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember
Ending balance: collectively evaluated for impaired | 1,397,466us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember | 1,284,321us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember | 1,224,538us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember
Loans to individuals [Member] |  |  |
Financing Receivable, Allowance for Credit Losses [Roll Forward] |  |  |
Beginning Balance | 5,457us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsMember | 4,132us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsMember | 4,244us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsMember
Charge-offs | (3,964)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsMember | (3,679)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsMember | (3,482)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsMember
Recoveries | 766us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsMember | 633us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsMember | 521us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsMember
Provision for credit losses | 2,557us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsMember | 4,371us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsMember | 2,849us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsMember
Ending Balance | 4,816us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsMember | 5,457us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsMember | 4,132us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsMember
Ending balance: individually evaluated for impaired | 0us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsMember | 0us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsMember | 0us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsMember
Ending balance: collectively evaluated for impaired | 4,816us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsMember | 5,457us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsMember | 4,132us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsMember
Ending balance | 652,814us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsMember | 610,298us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsMember | 582,218us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsMember
Ending balance: individually evaluated for impaired | 0us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsMember | 0us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsMember | 0us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsMember
Ending balance: collectively evaluated for impaired | 652,814us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsMember | 610,298us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsMember | 582,218us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsMember
Unallocated [Member] |  |  |
Financing Receivable, Allowance for Credit Losses [Roll Forward] |  |  |
Beginning Balance |  | 5,926us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember | 4,836us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember
Charge-offs |  | 0us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember | 0us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember
Recoveries |  | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember
Provision for credit losses |  | (5,926)us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember | 1,090us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember
Ending Balance |  | 0us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember | 5,926us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember
Ending balance: individually evaluated for impaired |  | 0us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember | 0us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember
Ending balance: collectively evaluated for impaired |  | $ 0us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember | $ 5,926us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember

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