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.

No definition available.

+ Details

Name:	us-gaap_FinancingReceivableModificationsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of financing receivables that have been modified by troubled debt restructurings within the previous 12 months and for which there was a payment default.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953682-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of investment related to financing receivables modified by troubled debt restructurings within the previous 12 months, for which there was a payment default.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=frme_CommercialAndIndustrialLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ResidentialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InternalCreditAssessmentAxis=frme_NonimpairedLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Loans and Allowance - Subsequent Default (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($) loan	Sep. 30, 2015 USD ($) loan	Sep. 30, 2016 USD ($) loan	Sep. 30, 2015 USD ($) loan
Financing Receivable, Modifications [Line Items]
Number of Loans \| loan	1	1	4	1
Recorded Balance \| $	$ 54	$ 21	$ 251	$ 21
Commercial and industrial loans
Financing Receivable, Modifications [Line Items]
Number of Loans \| loan			3
Recorded Balance \| $			$ 197
Real estate loans - Residential
Financing Receivable, Modifications [Line Items]
Number of Loans \| loan	1		1
Recorded Balance \| $	$ 54		$ 54
Nonimpaired loans \| Real estate loans - Residential
Financing Receivable, Modifications [Line Items]
Number of Loans \| loan		1		1
Recorded Balance \| $		$ 21		$ 21