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v3.20.2

Subsequent Events (Details) $ in Millions | Jun. 30, 2020 USD ($)
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Subsequent Events [Abstract] |
Subsequent Event Consolidation Related Expenses | $ 3.5
Estimated Subsequent Event Voluntary Retirement Plan Expenses | $ 7.0

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- Definition Estimated Subsequent Event Consolidation Related Expenses + References No definition available. + Details
Name: | fcf_EstimatedSubsequentEventConsolidationRelatedExpenses
Namespace Prefix: | fcf_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Estimated Subsequent Event Voluntary Retirement Plan Expenses + References No definition available. + Details
Name: | fcf_EstimatedSubsequentEventVoluntaryRetirementPlanExpenses
Namespace Prefix: | fcf_
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_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration