XML 50 R37.htm IDEA: XBRL DOCUMENT
v3.21.1

Investment Securities - Analysis of Amortized Cost and Estimated Fair Values of Securities Available for Sale (Detail) - USD ($) $ in Thousands | Mar. 31, 2021 | Dec. 31, 2020
--- | --- | ---
Investment Securities [Line Items] |  |
Amortized Cost | $ 1,033,361 | $ 805,515
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 17,822 | 25,708
Gross Unrealized Losses | (7,925) | 0
Securities available for sale, at fair value | 1,043,258 | 831,223
US Government Agencies Residential Mortgage-backed Securities [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 6,067 | 6,492
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 623 | 738
Gross Unrealized Losses | 0 | 0
Securities available for sale, at fair value | 6,690 | 7,230
US Government Agency Debt Securities Commercial [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 268,890 | 182,823
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 4,597 | 8,357
Gross Unrealized Losses | (586) | 0
Securities available for sale, at fair value | 272,901 | 191,180
Residential Mortgage Backed Securities [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 724,611 | 481,109
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 11,082 | 14,924
Gross Unrealized Losses | (7,025) | 0
Securities available for sale, at fair value | 728,668 | 496,033
US Government-sponsored Enterprises Debt Securities [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 1,000 | 100,996
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 0 | 2
Gross Unrealized Losses | (25) | 0
Securities available for sale, at fair value | 975 | 100,998
Obligations of States and Political Subdivisions [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 9,647 | 11,154
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 132 | 243
Gross Unrealized Losses | (214) | 0
Securities available for sale, at fair value | 9,565 | 11,397
Corporate Debt Securities [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 23,146 | 22,941
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 1,388 | 1,444
Gross Unrealized Losses | (75) | 0
Securities available for sale, at fair value | $ 24,459 | $ 24,385

X
- Definition Investment Securities [Line Items] + References No definition available. + Details
Name: | fcf_InvestmentSecuritiesLineItems
Namespace Prefix: | fcf_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563 + Details
Name: | us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563 + Details
Name: | us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading. + References No definition available. + Details
Name: | us-gaap_AvailableForSaleSecurities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any. + References No definition available. + Details
Name: | us-gaap_AvailableForSaleSecuritiesAmortizedCost
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_InvestmentTypeAxis=fcf_USGovernmentAgencyDebtSecuritiesResidentialDomain
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=fcf_USGovernmentAgencyDebtSecuritiesCommercialMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_ResidentialMortgageBackedSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |