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Loans and Allowance for Credit Losses - Recorded Investment and Unpaid Principal Balance for Impaired Loans with Associated Allowance (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, Impaired [Line Items] |  |  |
Recorded Investment | $ 55,251us-gaap_ImpairedFinancingReceivableRecordedInvestment | $ 59,383us-gaap_ImpairedFinancingReceivableRecordedInvestment |
Unpaid Principal Balance | 60,915us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance | 66,307us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance |
Related Allowance | 9,461us-gaap_ImpairedFinancingReceivableRelatedAllowance | 8,824us-gaap_ImpairedFinancingReceivableRelatedAllowance |
Average Recorded Investment | 49,794us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment | 78,175us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment | 87,979us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
Interest Income Recognized | 625us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod | 679us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod | 369us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
Commercial, financial, agricultural and other with no related allowance recorded [Member] |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Recorded Investment | 9,439us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherWithNoRelatedAllowanceMember | 6,752us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherWithNoRelatedAllowanceMember |
Unpaid Principal Balance | 10,937us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherWithNoRelatedAllowanceMember | 7,649us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherWithNoRelatedAllowanceMember |
Average Recorded Investment | 11,536us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherWithNoRelatedAllowanceMember | 14,454us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherWithNoRelatedAllowanceMember | 9,217us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherWithNoRelatedAllowanceMember
Interest Income Recognized | 133us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherWithNoRelatedAllowanceMember | 73us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherWithNoRelatedAllowanceMember | 173us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherWithNoRelatedAllowanceMember
Real estate construction with no related allowance recorded [Member] |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Recorded Investment | 236us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionWithNoRelatedAllowanceMember | 3,486us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionWithNoRelatedAllowanceMember |
Unpaid Principal Balance | 476us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionWithNoRelatedAllowanceMember | 6,664us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionWithNoRelatedAllowanceMember |
Average Recorded Investment | 1,190us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionWithNoRelatedAllowanceMember | 5,923us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionWithNoRelatedAllowanceMember | 11,912us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionWithNoRelatedAllowanceMember
Interest Income Recognized | 19us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionWithNoRelatedAllowanceMember | 47us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionWithNoRelatedAllowanceMember | 0us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionWithNoRelatedAllowanceMember
Residential real estate with no related allowance recorded [Member] |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Recorded Investment | 10,773us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_ResidentialRealEstateWithNoRelatedAllowanceMember | 9,333us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_ResidentialRealEstateWithNoRelatedAllowanceMember |
Unpaid Principal Balance | 12,470us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_ResidentialRealEstateWithNoRelatedAllowanceMember | 9,952us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_ResidentialRealEstateWithNoRelatedAllowanceMember |
Average Recorded Investment | 11,592us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_ResidentialRealEstateWithNoRelatedAllowanceMember | 9,280us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_ResidentialRealEstateWithNoRelatedAllowanceMember | 8,114us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_ResidentialRealEstateWithNoRelatedAllowanceMember
Interest Income Recognized | 210us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_ResidentialRealEstateWithNoRelatedAllowanceMember | 211us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_ResidentialRealEstateWithNoRelatedAllowanceMember | 72us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_ResidentialRealEstateWithNoRelatedAllowanceMember
Commercial real estate with no related allowance recorded [Member] |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Recorded Investment | 8,768us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialRealEstateWithNoRelatedAllowanceMember | 13,606us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialRealEstateWithNoRelatedAllowanceMember |
Unpaid Principal Balance | 10,178us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialRealEstateWithNoRelatedAllowanceMember | 14,719us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialRealEstateWithNoRelatedAllowanceMember |
Average Recorded Investment | 8,830us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialRealEstateWithNoRelatedAllowanceMember | 27,881us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialRealEstateWithNoRelatedAllowanceMember | 28,574us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialRealEstateWithNoRelatedAllowanceMember
Interest Income Recognized | 98us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialRealEstateWithNoRelatedAllowanceMember | 250us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialRealEstateWithNoRelatedAllowanceMember | 66us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialRealEstateWithNoRelatedAllowanceMember
Loans to individuals with no related allowance recorded [Member] |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Recorded Investment | 288us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsWithNoRelatedAllowanceMember | 289us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsWithNoRelatedAllowanceMember |
Unpaid Principal Balance | 337us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsWithNoRelatedAllowanceMember | 307us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsWithNoRelatedAllowanceMember |
Average Recorded Investment | 308us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsWithNoRelatedAllowanceMember | 255us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsWithNoRelatedAllowanceMember | 103us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsWithNoRelatedAllowanceMember
Interest Income Recognized | 4us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsWithNoRelatedAllowanceMember | 3us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsWithNoRelatedAllowanceMember | 2us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsWithNoRelatedAllowanceMember
Subtotal with no related allowance recorded [Member] |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Recorded Investment | 29,504us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_WithNoRelatedAllowanceMember | 33,466us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_WithNoRelatedAllowanceMember |
Unpaid Principal Balance | 34,398us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_WithNoRelatedAllowanceMember | 39,291us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_WithNoRelatedAllowanceMember |
Average Recorded Investment | 33,456us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_WithNoRelatedAllowanceMember | 57,793us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_WithNoRelatedAllowanceMember | 57,920us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_WithNoRelatedAllowanceMember
Interest Income Recognized | 464us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_WithNoRelatedAllowanceMember | 584us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_WithNoRelatedAllowanceMember | 313us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_WithNoRelatedAllowanceMember
Commercial, financial, agricultural and other With an allowance recorded [Member] |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Recorded Investment | 24,826us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherWithRelatedAllowanceMember | 21,482us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherWithRelatedAllowanceMember |
Unpaid Principal Balance | 25,583us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherWithRelatedAllowanceMember | 22,082us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherWithRelatedAllowanceMember |
Related Allowance | 9,304us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherWithRelatedAllowanceMember | 7,364us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherWithRelatedAllowanceMember |
Average Recorded Investment | 15,797us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherWithRelatedAllowanceMember | 16,479us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherWithRelatedAllowanceMember | 21,979us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherWithRelatedAllowanceMember
Interest Income Recognized | 143us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherWithRelatedAllowanceMember | 64us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherWithRelatedAllowanceMember | 9us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialFinancialAgriculturalAndOtherWithRelatedAllowanceMember
Real estate construction with an allowance recorded [Member] |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Recorded Investment | 0us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionWithRelatedAllowanceMember | 414us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionWithRelatedAllowanceMember |
Unpaid Principal Balance | 0us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionWithRelatedAllowanceMember | 737us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionWithRelatedAllowanceMember |
Related Allowance | 0us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionWithRelatedAllowanceMember | 94us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionWithRelatedAllowanceMember |
Average Recorded Investment | 0us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionWithRelatedAllowanceMember | 515us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionWithRelatedAllowanceMember | 1,457us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionWithRelatedAllowanceMember
Interest Income Recognized | 0us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionWithRelatedAllowanceMember | 0us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionWithRelatedAllowanceMember | 0us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_RealEstateConstructionWithRelatedAllowanceMember
Residential real estate With an allowance recorded [Member] |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Recorded Investment | 367us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_ResidentialRealEstateWithRelatedAllowanceMember | 3,533us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_ResidentialRealEstateWithRelatedAllowanceMember |
Unpaid Principal Balance | 380us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_ResidentialRealEstateWithRelatedAllowanceMember | 3,585us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_ResidentialRealEstateWithRelatedAllowanceMember |
Related Allowance | 56us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_ResidentialRealEstateWithRelatedAllowanceMember | 1,282us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_ResidentialRealEstateWithRelatedAllowanceMember |
Average Recorded Investment | 357us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_ResidentialRealEstateWithRelatedAllowanceMember | 3,200us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_ResidentialRealEstateWithRelatedAllowanceMember | 1,599us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_ResidentialRealEstateWithRelatedAllowanceMember
Interest Income Recognized | 14us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_ResidentialRealEstateWithRelatedAllowanceMember | 31us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_ResidentialRealEstateWithRelatedAllowanceMember | 15us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_ResidentialRealEstateWithRelatedAllowanceMember
Commercial real estate With an allowance recorded [Member] |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Recorded Investment | 554us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialRealEstateWithRelatedAllowanceMember | 488us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialRealEstateWithRelatedAllowanceMember |
Unpaid Principal Balance | 554us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialRealEstateWithRelatedAllowanceMember | 612us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialRealEstateWithRelatedAllowanceMember |
Related Allowance | 101us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialRealEstateWithRelatedAllowanceMember | 84us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialRealEstateWithRelatedAllowanceMember |
Average Recorded Investment | 184us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialRealEstateWithRelatedAllowanceMember | 188us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialRealEstateWithRelatedAllowanceMember | 5,024us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialRealEstateWithRelatedAllowanceMember
Interest Income Recognized | 4us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialRealEstateWithRelatedAllowanceMember | 0us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialRealEstateWithRelatedAllowanceMember | 32us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_CommercialRealEstateWithRelatedAllowanceMember
Loans to individuals With an allowance recorded [Member] |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Recorded Investment | 0us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsWithRelatedAllowanceMember | 0us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsWithRelatedAllowanceMember |
Unpaid Principal Balance | 0us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsWithRelatedAllowanceMember | 0us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsWithRelatedAllowanceMember |
Related Allowance | 0us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsWithRelatedAllowanceMember | 0us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsWithRelatedAllowanceMember |
Average Recorded Investment | 0us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsWithRelatedAllowanceMember | 0us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsWithRelatedAllowanceMember | 0us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsWithRelatedAllowanceMember
Interest Income Recognized | 0us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsWithRelatedAllowanceMember | 0us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsWithRelatedAllowanceMember | 0us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_LoansToIndividualsWithRelatedAllowanceMember
Subtotal With an allowance recorded [Member] |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Recorded Investment | 25,747us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_WithRelatedAllowanceMember | 25,917us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_WithRelatedAllowanceMember |
Unpaid Principal Balance | 26,517us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_WithRelatedAllowanceMember | 27,016us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_WithRelatedAllowanceMember |
Related Allowance | 9,461us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_WithRelatedAllowanceMember | 8,824us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_WithRelatedAllowanceMember |
Average Recorded Investment | 16,338us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_WithRelatedAllowanceMember | 20,382us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_WithRelatedAllowanceMember | 30,059us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_WithRelatedAllowanceMember
Interest Income Recognized | $ 161us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_WithRelatedAllowanceMember | $ 95us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_WithRelatedAllowanceMember | $ 56us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcf_WithRelatedAllowanceMember

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