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    <Log type="Info">'Monetary' elements on report '2458405 - Disclosure - Condensed Financial Information of First Commonwealth Financial Corporation (Parent Company Only) - Additional Information (Detail)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">Process Flow-Through: 1001000 - Statement - CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION</Log>
    <Log type="Info">	Process Flow-Through: Removing column 'Dec. 31, 2012'</Log>
    <Log type="Info">	Process Flow-Through: Removing column 'Dec. 31, 2011'</Log>
    <Log type="Info">Process Flow-Through: 1001501 - Statement - CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION (Parenthetical)</Log>
    <Log type="Info">Process Flow-Through: 1002000 - Statement - CONSOLIDATED STATEMENTS OF INCOME</Log>
    <Log type="Info">Process Flow-Through: 1003000 - Statement - CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME</Log>
    <Log type="Info">Process Flow-Through: 1004501 - Statement - CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (Parenthetical)</Log>
    <Log type="Info">	Process Flow-Through: Removing column '12 Months Ended
Dec. 31, 2014'</Log>
    <Log type="Info">Process Flow-Through: 1005000 - Statement - CONSOLIDATED STATEMENTS OF CASH FLOWS</Log>
  </Logs>
  <InputFiles>
    <File>fcf-20141231.xml</File>
    <File>fcf-20141231.xsd</File>
    <File>fcf-20141231_cal.xml</File>
    <File>fcf-20141231_def.xml</File>
    <File>fcf-20141231_lab.xml</File>
    <File>fcf-20141231_pre.xml</File>
  </InputFiles>
  <SupplementalFiles />
  <BaseTaxonomies />
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
