| **Commitments and Contingent Liabilities - Notional Amount of Outstanding Commitments (Detail) (USD $)In Thousands, unless otherwise specified** | Sep. 30, 2013 | Dec. 31, 2012 |
|--------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| Commitments to extend credit [Member]                                                                                                            |          |          |
| **Loss Contingencies [Line Items]**                                                                                                              |          |          |
| Financial instrument of credit risk                                                                                                              | $ 1,568,438   | $ 1,506,618   |
| Financial standby letters of credit [Member]                                                                                                     |          |          |
| **Loss Contingencies [Line Items]**                                                                                                              |          |          |
| Financial instrument of credit risk                                                                                                              | 40,245        | 47,185        |
| Performance standby letters of credit [Member]                                                                                                   |          |          |
| **Loss Contingencies [Line Items]**                                                                                                              |          |          |
| Financial instrument of credit risk                                                                                                              | 34,084        | 69,240        |
| Commercial letters of credit [Member]                                                                                                            |          |          |
| **Loss Contingencies [Line Items]**                                                                                                              |          |          |
| Financial instrument of credit risk                                                                                                              | $ 0           | $ 685         |

| X                                                                                                                                                                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Notional amount of outstanding commitments and letters of credit.
+ References
No definition available.
+ Details**Name:**fcf_NotionalAmountOfCommitmentsAndLettersOfCredit**Namespace Prefix:**fcf_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                              |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_LossContingenciesLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |