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v3.3.0.814

Subsequent Events (Details) $ in Millions | Oct. 01, 2015 USD ($)
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Subsequent Events [Abstract] |
Business Acquisition, Transaction Costs | $ 14.8
Total Acquired Assets | $ 102.8

X
- Definition Total Acquired Assets + References No definition available. + Details
Name: | fcf_TotalAcquiredAssets
Namespace Prefix: | fcf_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- 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

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