| **Variable Interest Entities - Schedule of Maximum Potential Exposure (Detail) (USD $)In Thousands, unless otherwise specified** | Mar. 31, 2013 | Dec. 31, 2012 |
|----------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Variable Interest Entities [Abstract]**                                                                                        |          |          |
| Low Income Housing Limited Partnership Investments                                                                               | $ 304         | $ 347         |

| X                                                                                                                                                            |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**fcf_VariableInterestEntitiesAbstract**Namespace Prefix:**fcf_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
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| - Definition
The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE).
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph b -URI http://asc.fasb.org/extlink&oid=7880789&loc=d3e5728-111685Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=7880789&loc=d3e5747-111685Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Staff Position (FSP) -Number FAS140-4/FIN46(R) -Paragraph C6 -Subparagraph b -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.
+ Details**Name:**us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |