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Subsequent Event (Details) $ in Millions | Jun. 30, 2016 USD ($) branch
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Subsequent Events [Abstract] |
Branch Acquisition, Number of Branches | branch | 13
Branch Acquisition, Total Deposits | $ 735
Branch Acquisition, Total Loans | $ 115

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- Definition Branch Acquisition, Number of Branches + References No definition available. + Details
Name: | fcf_BranchAcquisitionNumberofBranches
Namespace Prefix: | fcf_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Branch Acquisition, Total Deposits + References No definition available. + Details
Name: | fcf_BranchAcquisitionTotalDeposits
Namespace Prefix: | fcf_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Branch Acquisition, Total Loans + References No definition available. + Details
Name: | fcf_BranchAcquisitionTotalLoans
Namespace Prefix: | fcf_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- References No definition available. + Details
Name: | us-gaap_SubsequentEventsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration