| **Document and Entity Information Document** | Jun. 22, 2022                                                                                                                                                                       |
|----------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| **Document Information [Line Items]**        |                                                                                                                                                                                |
| Document Type                                | 8-K/A                                                                                                                                                                               |
| Document Period End Date                     | Jun. 22,  2022                                                                                                                                                                      |
| Entity Registrant Name                       | FIRST MERCHANTS CORP                                                                                                                                                                |
| Entity Incorporation, State or Country Code  | IN                                                                                                                                                                                  |
| Entity File Number                           | 001-41342                                                                                                                                                                           |
| Entity Tax Identification Number             | 35-1544218                                                                                                                                                                          |
| Entity Address, Address Line One             | 200 East Jackson Street                                                                                                                                                             |
| Entity Address, Address Line Two             | P.O. Box 792                                                                                                                                                                        |
| Entity Address, City or Town                 | Muncie                                                                                                                                                                              |
| Entity Address, State or Province            | IN                                                                                                                                                                                  |
| Entity Address, Postal Zip Code              | 47305-2814                                                                                                                                                                          |
| City Area Code                               | 765                                                                                                                                                                                 |
| Local Phone Number                           | 747-1500                                                                                                                                                                            |
| Written Communications                       | false                                                                                                                                                                               |
| Soliciting Material                          | false                                                                                                                                                                               |
| Pre-commencement Tender Offer                | false                                                                                                                                                                               |
| Pre-commencement Issuer Tender Offer         | false                                                                                                                                                                               |
| Entity Emerging Growth Company               | false                                                                                                                                                                               |
| Amendment Description                        | This Form 8-K/A is filed as an amendment (Amendment No. 1) to the Current Report on Form 8-K filed by First Merchants Corporation under Items 5.02, 5.03 and 9.01 on June 23, 2022. |
| Entity Central Index Key                     | 0000712534                                                                                                                                                                          |
| Amendment Flag                               | true                                                                                                                                                                                |
| Common Stock                                 |                                                                                                                                                                                |
| **Document Information [Line Items]**        |                                                                                                                                                                                |
| Title of 12(b) Security                      | Common Stock, $0.125 stated value per share                                                                                                                                         |
| Trading Symbol                               | FRME                                                                                                                                                                                |
| Security Exchange Name                       | NASDAQ                                                                                                                                                                              |
| Depositary Shares                            |                                                                                                                                                                                |
| **Document Information [Line Items]**        |                                                                                                                                                                                |
| Title of 12(b) Security                      | Depositary Shares, each representing a 1/100th interest in a share of Non-Cumulative Perpetual Preferred Stock, Series A                                                            |
| Trading Symbol                               | FRMEP                                                                                                                                                                               |
| Security Exchange Name                       | NASDAQ                                                                                                                                                                              |

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Description of changes contained within amended document.
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Boolean flag that is true when the XBRL content amends previously-filed or accepted submission.
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Area code of city
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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.
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For the EDGAR submission types of Form 8-K: the date of the report, the date of the earliest event reported; for the EDGAR submission types of Form N-1A: the filing date; for all other submission types: the end of the reporting or transition period.  The format of the date is YYYY-MM-DD.
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The type of document being provided (such as 10-K, 10-Q, 485BPOS, etc). The document type is limited to the same value as the supporting SEC submission type, or the word 'Other'.
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Address Line 1 such as Attn, Building Name, Street Name
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Address Line 2 such as Street or Suite number
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Name of the City or Town
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Code for the postal or zip code
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Name of the state or province.
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| - Definition
A unique 10-digit SEC-issued value to identify entities that have filed disclosures with the SEC. It is commonly abbreviated as CIK.
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Indicate if registrant meets the emerging growth company criteria.
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Commission file number. The field allows up to 17 characters. The prefix may contain 1-3 digits, the sequence number may contain 1-8 digits, the optional suffix may contain 1-4 characters, and the fields are separated with a hyphen.
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Two-character EDGAR code representing the state or country of incorporation.
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The exact name of the entity filing the report as specified in its charter, which is required by forms filed with the SEC.
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The Tax Identification Number (TIN), also known as an Employer Identification Number (EIN), is a unique 9-digit value assigned by the IRS.
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Local phone number for entity.
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Boolean flag that is true when the Form 8-K filing is intended to satisfy the filing obligation of the registrant as pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act.
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Boolean flag that is true when the Form 8-K filing is intended to satisfy the filing obligation of the registrant as pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act.
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Title of a 12(b) registered security.
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Name of the Exchange on which a security is registered.
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Boolean flag that is true when the Form 8-K filing is intended to satisfy the filing obligation of the registrant as soliciting material pursuant to Rule 14a-12 under the Exchange Act.
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Trading symbol of an instrument as listed on an exchange.
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Boolean flag that is true when the Form 8-K filing is intended to satisfy the filing obligation of the registrant as written communications pursuant to Rule 425 under the Securities Act.
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