Name:	frme_EBPEmployerContributionAnnualFixedRateContributionPercentage
Namespace Prefix:	frme_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

Company contribution and/ or investment earning percentage vesting to the participant in Company Matching Contributions, Fixed Rate Contributions, Discretionary Profit-Sharing Contributions, Qualified Non-Elective Contributions, and Disability Contributions, upon completion of minimum service period or attainment of maximum vesting age

No definition available.

Name:	frme_EBPEmployerContributionVestingPercentage
Namespace Prefix:	frme_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

EBP, Employer Contribution Vesting Service Hours

No definition available.

Name:	frme_EBPEmployerContributionVestingServiceHours
Namespace Prefix:	frme_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Minimum Vesting service period for company contribution and/ or investment earning to the participant in Company Matching Contributions, Fixed Rate Contributions, Discretionary Profit-Sharing Contributions, Qualified Non-Elective Contributions, and Disability Contributions.

No definition available.

Name:	frme_EBPEmployerContributionVestingServicePeriod
Namespace Prefix:	frme_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

EBP, Employer Participant Service Period

No definition available.

Name:	frme_EBPEmployerParticipantServicePeriod
Namespace Prefix:	frme_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

EBP, Note Receivable From Participant, General Loan, Maximum Borrowing Term

No definition available.

Name:	frme_EBPNoteReceivableFromParticipantGeneralLoanMaximumBorrowingTerm
Namespace Prefix:	frme_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

EBP, Participant Account, Maximum Plan Investment Balance, Percent

No definition available.

Name:	frme_EBPParticipantAccountMaximumPlanInvestmentBalancePercent
Namespace Prefix:	frme_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

EBP, Participant Contribution, Automatic, Deferral Decline Period

No definition available.

Name:	frme_EBPParticipantContributionAutomaticDeferralDeclinePeriod
Namespace Prefix:	frme_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

EBP, Requisite Participant Age

No definition available.

Name:	frme_EBPRequisiteParticipantAge
Namespace Prefix:	frme_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

EBP, Requisite Service Hours

No definition available.

Name:	frme_EBPRequisiteServiceHours
Namespace Prefix:	frme_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

EBP, Retirement Age

No definition available.

Name:	frme_EBPRetirementAge
Namespace Prefix:	frme_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

EBP, Retirement Service Period

No definition available.

Name:	frme_EBPRetirementServicePeriod
Namespace Prefix:	frme_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

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.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-SubTopic 205
-Topic 962
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478416/962-205-50-1

Name:	us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanLineItems
Namespace Prefix:	us-gaap-ebp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Percentage of employer matching contribution on eligible participant contribution to employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

Name:	us-gaap-ebp_EmployeeBenefitPlanEmployerContributionMatchingPercentage
Namespace Prefix:	us-gaap-ebp_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

Percentage of participant compensation eligible for employer matching contribution for participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

Name:	us-gaap-ebp_EmployeeBenefitPlanEmployerContributionParticipantCompensationMatchedPercentage
Namespace Prefix:	us-gaap-ebp_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

Amount of plan asset, in forfeited nonvested account, no longer allocated to participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

Name:	us-gaap-ebp_EmployeeBenefitPlanForfeitedNonvestedAccount
Namespace Prefix:	us-gaap-ebp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Amount of decrease in forfeited nonvested account of employee stock purchase, saving, or similar plan (employee benefit plan (EBP)) from administrative expense.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (j)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478416/962-205-50-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6A-04(5)(c))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477804/962-205-S99-1

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Namespace Prefix:	us-gaap-ebp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Amount of decrease in forfeited nonvested account of employee stock purchase, saving, or similar plan (employee benefit plan (EBP)) from employer contribution.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 962
-SubTopic 325
-Name Accounting Standards Codification
-Section 55
-Paragraph 17
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478873/962-325-55-17

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (j)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478416/962-205-50-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6A-04(5)(c))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477804/962-205-S99-1

Name:	us-gaap-ebp_EmployeeBenefitPlanForfeitedNonvestedAccountDecreaseForEmployerContribution
Namespace Prefix:	us-gaap-ebp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Amount of maximum account balance that participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)) can borrow.

Name:	us-gaap-ebp_EmployeeBenefitPlanNoteReceivableFromParticipantAccountMaximumBorrowingAmount
Namespace Prefix:	us-gaap-ebp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Percentage of maximum account balance that participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)) can borrow to total participant account balance.

Name:	us-gaap-ebp_EmployeeBenefitPlanNoteReceivableFromParticipantAccountMaximumBorrowingToTotalAccountPercentage
Namespace Prefix:	us-gaap-ebp_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

Amount of minimum account balance that participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)) can borrow.

Name:	us-gaap-ebp_EmployeeBenefitPlanNoteReceivableFromParticipantAccountMinimumBorrowingAmount
Namespace Prefix:	us-gaap-ebp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Percentage of eligible compensation contributed for participant automatically enrolled in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

Name:	us-gaap-ebp_EmployeeBenefitPlanParticipantContributionAutomaticDeferralRate
Namespace Prefix:	us-gaap-ebp_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

Percentage of maximum pretax annual compensation that participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)), is permitted to contribute to total pretax annual compensation.

Name:	us-gaap-ebp_EmployeeBenefitPlanParticipantContributionPretaxMaximumAnnualCompensationToTotalCompensationPercentage
Namespace Prefix:	us-gaap-ebp_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

Name:	dei_LegalEntityAxis=frme_EBP002Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_InvestmentTypeAxis=us-gaap-ebp_EmployeeBenefitPlanEmployerCommonStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_InvestmentTypeAxis=us-gaap-ebp_EmployeeBenefitPlanSelfDirectedBrokerageAccountMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	frme_EBPEmployerContributionTypeAxis=frme_EBPRetirementSecurityContributionRSCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	frme_EBPEmployerContributionTypeAxis=frme_EBPEmployerMatchingContributionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	frme_EBPEmployerContributionTypeAxis=frme_EBPEmployerMatchingContributionsTrancheOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: