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Fair Values of Assets and Liabilities - Losses Realized on Assets Measured on Non-Recurring Basis (Detail) - USD ($) $ in Thousands | 3 Months Ended
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Mar. 31, 2023 | Mar. 31, 2022
Fair Value Disclosures [Abstract] |  |
Impaired loans | $ 230 | $ (171)
Other real estate owned | 0 | (54)
Total losses | $ 230 | $ (225)

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- Definition Net losses on assets measured on nonrecurring basis. + References No definition available. + Details
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- Definition Net losses on impaired loans still held at the end of the period. + References No definition available. + Details
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- Definition Net losses on other real estate owned still held at the end of the period + References No definition available. + Details
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Namespace Prefix: | fcf_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
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