NONEXEMPT TRANSACTION (Details) - EBP 002	12 Months Ended
Dec. 31, 2024 USD ($)
EBP, Contribution [Line Items]
Corrective contributions	$ 781
Corrective earnings	$ 18

EBP, Schedule of Delinquent Participant Contribution, Lost Earnings Fully Funded

No definition available.

Name:	frme_EBPScheduleOfDelinquentParticipantContributionLostEarningsFullyFunded
Namespace Prefix:	frme_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- 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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6A-04(4)(b))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477804/962-205-S99-1

+ Details

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

- Definition

Amount of delinquent participant contribution corrected outside Voluntary Fiduciary Correction Program (VFCP) for employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name Employee Retirement Income Security Act of 1974
-Number 2520
-Section 103
-Subsection 10
-Paragraph a
-Publisher DOL-EBSA

+ Details

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

- Details

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