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Commitments and Letters of Credit - Notional Amount of Commitments and Letter of Credit Instruments (Detail) - USD ($) $ in Thousands | Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
--- | --- | --- | ---
Loss Contingencies [Line Items] |  |  |
Commitments Net | $ 83 | $ 76 | $ 71
Commitments to extend credit |  |  |
Loss Contingencies [Line Items] |  |  |
Financial instrument of credit risk | 2,356,539 | 2,353,991 |
Financial standby letters of credit |  |  |
Loss Contingencies [Line Items] |  |  |
Financial instrument of credit risk | 18,417 | 18,824 |
Performance standby letters of credit |  |  |
Loss Contingencies [Line Items] |  |  |
Financial instrument of credit risk | 12,853 | 10,663 |
Commercial letters of credit |  |  |
Loss Contingencies [Line Items] |  |  |
Financial instrument of credit risk | $ 573 | $ 975 |

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- Definition Total commitments. + References No definition available. + Details
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Namespace Prefix: | fcf_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Notional amount of outstanding commitments and letters of credit. + References No definition available. + Details
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Namespace Prefix: | fcf_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Details
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- Details
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- Details
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- Details
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