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Subsequent Event (Details) | Sep. 30, 2016 USD ($) branch
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Subsequent Events [Abstract] |
Business Acquisition, Share Price | $ 14.50
Business Acquisition, Transaction Costs | 106,000,000.00
Business Acquisition, Total Assets | $ 556,000,000
Branch Acquisition, Number of Branches | branch | 9
Branch Acquisition, Total Deposits | $ 467,000,000
Branch Acquisition, Total Loans | $ 397,000,000

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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

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- Definition Business Acquisition, Total Assets + References No definition available. + Details
Name: | fcf_BusinessAcquisitionTotalAssets
Namespace Prefix: | fcf_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

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

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- Definition Business acquisition, Price + References No definition available. + Details
Name: | fcf_BusinessacquisitionPrice
Namespace Prefix: | fcf_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Amount of direct costs of the business combination including legal, accounting, and other costs incurred to consummate the business acquisition. + References No definition available. + Details
Name: | us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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