| **Fair Values of Assets and Liabilities - Schedule of Assets Measured on Non-Recurring Basis (Detail) (USD $)In Thousands, unless otherwise specified** | Mar. 31, 2013 | Dec. 31, 2012 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                        |          |          |
| Total Assets                                                                                                                                            |          | $ 1,216,011   |
| Fair Value, Measurements, Non-recurring [Member]                                                                                                        |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                        |          |          |
| Impaired loans                                                                                                                                          | 65,592        | 89,776        |
| Other real estate owned                                                                                                                                 | 11,604        | 12,228        |
| Total Assets                                                                                                                                            | 77,196        | 102,004       |
| Level 1 [Member]                                                                                                                                        |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                        |          |          |
| Total Assets                                                                                                                                            | 513           | 555           |
| Level 1 [Member] | Fair Value, Measurements, Non-recurring [Member]                                                                                     |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                        |          |          |
| Impaired loans                                                                                                                                          | 0             | 0             |
| Other real estate owned                                                                                                                                 | 0             | 0             |
| Total Assets                                                                                                                                            | 0             | 0             |
| Level 2 [Member]                                                                                                                                        |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                        |          |          |
| Total Assets                                                                                                                                            | 1,315,878     | 1,190,663     |
| Level 2 [Member] | Fair Value, Measurements, Non-recurring [Member]                                                                                     |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                        |          |          |
| Impaired loans                                                                                                                                          | 57,636        | 82,949        |
| Other real estate owned                                                                                                                                 | 11,389        | 11,981        |
| Total Assets                                                                                                                                            | 69,025        | 94,930        |
| Level 3 [Member]                                                                                                                                        |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                        |          |          |
| Total Assets                                                                                                                                            | 25,932        | 24,793        |
| Level 3 [Member] | Fair Value, Measurements, Non-recurring [Member]                                                                                     |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                        |          |          |
| Impaired loans                                                                                                                                          | 7,956         | 6,827         |
| Other real estate owned                                                                                                                                 | 215           | 247           |
| Total Assets                                                                                                                                            | $ 8,171       | $ 7,074       |

| X                                                                                                                                                                                                                                    |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Impaired loans fair value.
+ References
No definition available.
+ Details**Name:**fcf_ImpairedLoansFairValue**Namespace Prefix:**fcf_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Other real estate owned assets fair value.
+ References
No definition available.
+ Details**Name:**fcf_OtherRealEstateOwnedAssetsFairValue**Namespace Prefix:**fcf_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258
+ Details**Name:**us-gaap_AssetsFairValueDisclosure**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |