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Commitments and Contingent Liabilities - Notional Amount of Outstanding Commitments (Detail) - USD ($) $ in Thousands | Mar. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Commitments to extend credit [Member] |  |
Loss Contingencies [Line Items] |  |
Financial instrument of credit risk | $ 1,687,588 | $ 1,733,820
Financial standby letters of credit [Member] |  |
Loss Contingencies [Line Items] |  |
Financial instrument of credit risk | 16,894 | 18,108
Performance standby letters of credit [Member] |  |
Loss Contingencies [Line Items] |  |
Financial instrument of credit risk | 27,169 | 26,630
Commercial letters of credit [Member] |  |
Loss Contingencies [Line Items] |  |
Financial instrument of credit risk | $ 1,142 | $ 1,301

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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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Namespace Prefix: | us-gaap_
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- Details
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- Details
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Namespace Prefix: |
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- Details
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- Details
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Namespace Prefix: |
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