|**Fair Values of Assets and Liabilities - Quantitative Inputs and Assumptions Used in Level 3 Fair Value Measurements (Detail) (USD $)**                                                                                                                                                                                                                                                                                                                            | 12 Months Ended                                                                                                                                                                                                                                                                    |                                                                                                                   
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------
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|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Other Assets                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 11,186,000us-gaap_OtherAssetsFairValueDisclosure                                                                                                                                                                                                                                   |                                                                                                                   
|Estimated Fair Value of Available for Sale                                                                                                                                                                                                                                                                                                                                                                                                                          | 1,309,819,000us-gaap_AvailableForSaleSecurities                                                                                                                                                                                                                                    |                                                                                                                   
|Total Debt Securities                                                                                                                                                                                                                                                                                                                                                                                                                                               | 1,308,399,000us-gaap_DebtInstrumentFairValue                                                                                                                                                                                                                                       |                                                                                                                   
|Fair Value                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 1,368,052,000us-gaap_AssetsFairValueDisclosure                                                                                                                                                                                                                                     |                                                                                                                   
|Probability of default [Member] | Minimum [Member]                                                                                                                                                                                                                                                                                                                                                                                                                  |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Weighted average rate                                                                                                                                                                                                                                                                                                                                                                                                                                               | 0.00%us-gaap_FairValueInputsDiscountRate/ us-gaap_FairValueByMeasurementBasisAxis= fcf_ProbabilityOfDefaultMember/ us-gaap_RangeAxis= us-gaap_MinimumMember                                                                                                                        |                                                                                                                   
|Probability of default [Member] | Maximum [Member]                                                                                                                                                                                                                                                                                                                                                                                                                  |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Weighted average rate                                                                                                                                                                                                                                                                                                                                                                                                                                               | 100.00%us-gaap_FairValueInputsDiscountRate/ us-gaap_FairValueByMeasurementBasisAxis= fcf_ProbabilityOfDefaultMember/ us-gaap_RangeAxis= us-gaap_MaximumMember                                                                                                                      |                                                                                                                   
|Probability of default [Member] | Weighted Average [Member]                                                                                                                                                                                                                                                                                                                                                                                                         |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Weighted average rate                                                                                                                                                                                                                                                                                                                                                                                                                                               | 17.16%us-gaap_FairValueInputsDiscountRate/ us-gaap_FairValueByMeasurementBasisAxis= fcf_ProbabilityOfDefaultMember/ us-gaap_RangeAxis= us-gaap_WeightedAverageMember                                                                                                               |                                                                                                                   
|Prepayment rates [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Unobservable Inputs                                                                                                                                                                                                                                                                                                                                                                                                                                                 | Prepayment rates                                                                                                                                                                                                                                                                   |                                                                                                                   
|Prepayment rates [Member] | Minimum [Member]                                                                                                                                                                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Weighted average rate                                                                                                                                                                                                                                                                                                                                                                                                                                               | 0.00%us-gaap_FairValueInputsDiscountRate/ us-gaap_FairValueByMeasurementBasisAxis= fcf_PrepaymentRatesMember/ us-gaap_RangeAxis= us-gaap_MinimumMember                                                                                                                             |                                                                                                                   
|Prepayment rates [Member] | Maximum [Member]                                                                                                                                                                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Weighted average rate                                                                                                                                                                                                                                                                                                                                                                                                                                               | 73.88%us-gaap_FairValueInputsDiscountRate/ us-gaap_FairValueByMeasurementBasisAxis= fcf_PrepaymentRatesMember/ us-gaap_RangeAxis= us-gaap_MaximumMember                                                                                                                            |                                                                                                                   
|Prepayment rates [Member] | Weighted Average [Member]                                                                                                                                                                                                                                                                                                                                                                                                               |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Weighted average rate                                                                                                                                                                                                                                                                                                                                                                                                                                               | 6.13%us-gaap_FairValueInputsDiscountRate/ us-gaap_FairValueByMeasurementBasisAxis= fcf_PrepaymentRatesMember/ us-gaap_RangeAxis= us-gaap_WeightedAverageMember                                                                                                                     |                                                                                                                   
|Discount rates [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                             |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Unobservable Inputs                                                                                                                                                                                                                                                                                                                                                                                                                                                 | Discount rates                                                                                                                                                                                                                                                                     |                                                                                                                   
|Gas per MCF [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Unobservable Inputs                                                                                                                                                                                                                                                                                                                                                                                                                                                 | Gas per MCF                                                                                                                                                                                                                                                                        |                                                                                                                   
|Gas per MCF [Member] | Minimum [Member]                                                                                                                                                                                                                                                                                                                                                                                                                             |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Weighted average                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 3.00fcf_FairValueWeightedAverageInputsPrice/ us-gaap_FairValueByMeasurementBasisAxis= fcf_GasPerMillionCubicFeetMember/ us-gaap_RangeAxis= us-gaap_MinimumMember                                                                                                                   | [1]                                                                                                               
|Gas per MCF [Member] | Maximum [Member]                                                                                                                                                                                                                                                                                                                                                                                                                             |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Weighted average                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 4.85fcf_FairValueWeightedAverageInputsPrice/ us-gaap_FairValueByMeasurementBasisAxis= fcf_GasPerMillionCubicFeetMember/ us-gaap_RangeAxis= us-gaap_MaximumMember                                                                                                                   | [1]                                                                                                               
|Oil per BBL/d [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Unobservable Inputs                                                                                                                                                                                                                                                                                                                                                                                                                                                 | Oil per BBL/d                                                                                                                                                                                                                                                                      |                                                                                                                   
|Oil per BBL/d [Member] | Minimum [Member]                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Weighted average                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 53.91fcf_FairValueWeightedAverageInputsPrice/ us-gaap_FairValueByMeasurementBasisAxis= fcf_OilPerBarrelsPerDayMember/ us-gaap_RangeAxis= us-gaap_MinimumMember                                                                                                                     | [1]                                                                                                               
|Oil per BBL/d [Member] | Maximum [Member]                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Weighted average                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 71.01fcf_FairValueWeightedAverageInputsPrice/ us-gaap_FairValueByMeasurementBasisAxis= fcf_OilPerBarrelsPerDayMember/ us-gaap_RangeAxis= us-gaap_MaximumMember                                                                                                                     | [1]                                                                                                               
|NGL per gallon [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                             |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Unobservable Inputs                                                                                                                                                                                                                                                                                                                                                                                                                                                 | NGL per gallon                                                                                                                                                                                                                                                                     |                                                                                                                   
|NGL per gallon [Member] | Weighted Average [Member]                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Weighted average                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 0.83fcf_FairValueWeightedAverageInputsPrice/ us-gaap_FairValueByMeasurementBasisAxis= fcf_NaturalGasLiquidPerGallonMember/ us-gaap_RangeAxis= us-gaap_WeightedAverageMember                                                                                                        |                                                                                                                   
|Pooled Trust Preferred Collateralized Debt Obligations [Member] | Probability of default [Member]                                                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Unobservable Inputs                                                                                                                                                                                                                                                                                                                                                                                                                                                 | Probability of default                                                                                                                                                                                                                                                             |                                                                                                                   
|Pooled Trust Preferred Collateralized Debt Obligations [Member] | Discount rates [Member] | Minimum [Member]                                                                                                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Weighted average rate                                                                                                                                                                                                                                                                                                                                                                                                                                               | 5.25%us-gaap_FairValueInputsDiscountRate/ us-gaap_FairValueByMeasurementBasisAxis= fcf_DiscountRatesMember/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis= fcf_PooledTrustPreferredCollateralizedDebtObligationsMember/ us-gaap_RangeAxis= us-gaap_MinimumMember                   | [2]                                                                                                               
|Pooled Trust Preferred Collateralized Debt Obligations [Member] | Discount rates [Member] | Maximum [Member]                                                                                                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Weighted average rate                                                                                                                                                                                                                                                                                                                                                                                                                                               | 14.00%us-gaap_FairValueInputsDiscountRate/ us-gaap_FairValueByMeasurementBasisAxis= fcf_DiscountRatesMember/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis= fcf_PooledTrustPreferredCollateralizedDebtObligationsMember/ us-gaap_RangeAxis= us-gaap_MaximumMember                  | [2]                                                                                                               
|Pooled Trust Preferred Collateralized Debt Obligations [Member] | Discounted Cash Flow [Member]                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Valuation Technique                                                                                                                                                                                                                                                                                                                                                                                                                                                 | Discounted Cash Flow                                                                                                                                                                                                                                                               |                                                                                                                   
|Other Investments [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                          |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Unobservable Inputs                                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Other Investments [Member] | Par Value [Member]                                                                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Valuation Technique                                                                                                                                                                                                                                                                                                                                                                                                                                                 | Par Value                                                                                                                                                                                                                                                                          |                                                                                                                   
|Impaired Loans [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                             |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Fair Value                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 4,116,000us-gaap_AssetsFairValueDisclosure/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis= fcf_ImpairedLoansMember                                                                                                                                                                 | [3]                                                                                                               
|Impaired Loans [Member] | Weighted Average [Member]                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Weighted average rate                                                                                                                                                                                                                                                                                                                                                                                                                                               | 10.00%us-gaap_FairValueInputsDiscountRate/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis= fcf_ImpairedLoansMember/ us-gaap_RangeAxis= us-gaap_WeightedAverageMember                                                                                                                |                                                                                                                   
|Impaired Loans [Member] | Discount rates [Member]                                                                                                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Unobservable Inputs                                                                                                                                                                                                                                                                                                                                                                                                                                                 | Discount rate                                                                                                                                                                                                                                                                      |                                                                                                                   
|Impaired Loans [Member] | Reserve study [Member]                                                                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Valuation Technique                                                                                                                                                                                                                                                                                                                                                                                                                                                 | Gas Reserve study                                                                                                                                                                                                                                                                  |                                                                                                                   
|Other Real Estate Owned [Member] | Counterparty credit risk [Member]                                                                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Unobservable Inputs                                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Other Real Estate Owned [Member] | Internal Valuation [Member]                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Valuation Technique                                                                                                                                                                                                                                                                                                                                                                                                                                                 | Internal Valuation                                                                                                                                                                                                                                                                 |                                                                                                                   
|Fair Value, Inputs, Level 3 [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Other Assets                                                                                                                                                                                                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Estimated Fair Value of Available for Sale                                                                                                                                                                                                                                                                                                                                                                                                                          | 30,419,000us-gaap_AvailableForSaleSecurities/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member                                                                                                                                                  |                                                                                                                   
|Total Debt Securities                                                                                                                                                                                                                                                                                                                                                                                                                                               | 28,999,000us-gaap_DebtInstrumentFairValue/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member                                                                                                                                                     |                                                                                                                   
|Fair Value                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 30,419,000us-gaap_AssetsFairValueDisclosure/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member                                                                                                                                                   |                                                                                                                   
|Fair Value, Inputs, Level 3 [Member] | Interest rate swap [Member]                                                                                                                                                                                                                                                                                                                                                                                                  |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Other Assets                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 0us-gaap_OtherAssetsFairValueDisclosure/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis= us-gaap_InterestRateSwapMember                                                                        |                                                                                                                   
|Equities [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Estimated Fair Value of Available for Sale                                                                                                                                                                                                                                                                                                                                                                                                                          | 1,420,000us-gaap_AvailableForSaleSecurities/ us-gaap_FairValueByAssetClassAxis= us-gaap_EquitySecuritiesMember                                                                                                                                                                     |                                                                                                                   
|Equities [Member] | Fair Value, Inputs, Level 3 [Member]                                                                                                                                                                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Estimated Fair Value of Available for Sale                                                                                                                                                                                                                                                                                                                                                                                                                          |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Equities [Member] | Fair Value, Inputs, Level 3 [Member] | Other Investments [Member]                                                                                                                                                                                                                                                                                                                                                                               |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Estimated Fair Value of Available for Sale                                                                                                                                                                                                                                                                                                                                                                                                                          | 1,420,000us-gaap_AvailableForSaleSecurities/ us-gaap_FairValueByAssetClassAxis= us-gaap_EquitySecuritiesMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis= us-gaap_OtherInvestmentsMember |                                                                                                                   
|Fair Value, Measurements, Nonrecurring [Member]                                                                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Other real estate owned                                                                                                                                                                                                                                                                                                                                                                                                                                             | 7,981,000fcf_OtherRealEstateOwnedAssetsFairValue/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsNonrecurringMember                                                                                                                                     |                                                                                                                   
|Fair Value                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 53,771,000us-gaap_AssetsFairValueDisclosure/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsNonrecurringMember                                                                                                                                          |                                                                                                                   
|Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member]                                                                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                    |                                                                                                                   
|Other real estate owned                                                                                                                                                                                                                                                                                                                                                                                                                                             | 153,000fcf_OtherRealEstateOwnedAssetsFairValue/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsNonrecurringMember                                                  |                                                                                                                   
|Fair Value                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 11,079,000us-gaap_AssetsFairValueDisclosure/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsNonrecurringMember                                                     |                                                                                                                   
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|[1]
              unobservable inputs are defined as follows: MCF—million cubic feet; BBL/d—barrels per day; NGL—natural gas liquid.[2]
              incorporates spread over the risk free rate related primarily to credit quality and illiquidity of securities.[3]
              the remainder of impaired loans valued using Level 3 inputs are not included in this disclosure as the values of those loans are based on bankruptcy agreement documentation. | [1]                                                                                                                                                                                                                                                                                | unobservable inputs are defined as follows: MCF—million cubic feet; BBL/d—barrels per day; NGL—natural gas liquid.
|[1]                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | unobservable inputs are defined as follows: MCF—million cubic feet; BBL/d—barrels per day; NGL—natural gas liquid.                                                                                                                                                                
|[2]                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | incorporates spread over the risk free rate related primarily to credit quality and illiquidity of securities.                                                                                                                                                                    
|[3]                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | the remainder of impaired loans valued using Level 3 inputs are not included in this disclosure as the values of those loans are based on bankruptcy agreement documentation.                                                                                                     

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