| **Loans and Allowance for Credit Losses - Troubled Debt Restructured Loans and Commitments (Detail) (USD $)In Thousands, unless otherwise specified** | Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|---------------|
| **Loans and Leases Receivable Disclosure [Abstract]**                                                                                                 |          |          |          |
| Accrual status                                                                                                                                        | $ 13,495      | $ 13,037      | $ 20,276      |
| Nonaccrual status                                                                                                                                     | 16,980        | 50,979        | 44,841        |
| Total                                                                                                                                                 | 30,475        | 64,016        | 65,117        |
| Letters of credit                                                                                                                                     | 0             | 1,574         | 12,580        |
| Unused lines of credit                                                                                                                                | 452           | 0             | 42            |
| Total                                                                                                                                                 | $ 452         | $ 1,574       | $ 12,622      |

| X                                                                                                                                                                                                                     |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Total commitments.
+ References
No definition available.
+ Details**Name:**fcf_CommitmentsNet**Namespace Prefix:**fcf_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                       |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Financing receivable troubled debt restructured loans accrual status.
+ References
No definition available.
+ Details**Name:**fcf_FinancingReceivableTroubledDebtRestructuredLoansAccrualStatus**Namespace Prefix:**fcf_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                              |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Financing receivable troubled debt restructured loans non-accrual status.
+ References
No definition available.
+ Details**Name:**fcf_FinancingReceivableTroubledDebtRestructuredLoansNonaccrualStatus**Namespace Prefix:**fcf_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                     |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Troubled debt restructuring loans.
+ References
No definition available.
+ Details**Name:**fcf_TroubledDebtRestructuringLoans**Namespace Prefix:**fcf_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The total amount of unused lines of credit associated with troubled debt restructured loans as of the reporting date.
+ References
No definition available.
+ Details**Name:**fcf_UnusedLineOfCreditTroubledDebtRestructured**Namespace Prefix:**fcf_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                        |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.
+ References
No definition available.
+ Details**Name:**us-gaap_LettersOfCreditOutstandingAmount**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                              |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_LoansAndLeasesReceivableDisclosureAbstract**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |