XML 52 R39.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Commitments and Contingent Liabilities - Notional Amount of Outstanding Commitments (Detail) - USD ($) $ in Thousands | Mar. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Commitments to extend credit [Member] |  |
Loss Contingencies [Line Items] |  |
Financial instrument of credit risk | $ 1,782,701 | $ 1,840,180
Financial standby letters of credit [Member] |  |
Loss Contingencies [Line Items] |  |
Financial instrument of credit risk | 17,636 | 17,946
Performance standby letters of credit [Member] |  |
Loss Contingencies [Line Items] |  |
Financial instrument of credit risk | 21,328 | 20,472
Commercial letters of credit [Member] |  |
Loss Contingencies [Line Items] |  |
Financial instrument of credit risk | $ 1,055 | $ 1,149

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

X
- 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
Name: | us-gaap_LossContingenciesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_LossContingenciesByNatureOfContingencyAxis=us-gaap_CommitmentsToExtendCreditMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LossContingenciesByNatureOfContingencyAxis=us-gaap_FinancialStandbyLetterOfCreditMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LossContingenciesByNatureOfContingencyAxis=us-gaap_PerformanceGuaranteeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LossContingenciesByNatureOfContingencyAxis=fcf_CommercialLettersOfCreditMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |