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BORROWINGS - Narrative (Details) |  |  | 9 Months Ended | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Dec. 18, 2024 | Nov. 01, 2013 USD ($) investor | Sep. 30, 2024 USD ($) | Dec. 31, 2024 USD ($) | Dec. 31, 2023 USD ($) | Mar. 31, 2025 USD ($) | Jun. 30, 2024 USD ($) | Mar. 31, 2024 USD ($) | Dec. 18, 2019 USD ($)
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Total available remaining borrowing capacity from FHLB |  |  |  | $ 733,100,000 |  |  |  |  |
Putable advances with the FHLB |  |  |  | 822,554,000 | $ 712,852,000 |  |  |  |
Debt face amount |  | $ 70,000,000 |  |  |  |  |  |  |
Private debt issuance, number of institutional investors | investor |  | 4 |  |  |  |  |  |  |
Senior Notes |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Fixed interest rate term |  | 10 years |  |  |  |  |  |  |
5.00% Senior Notes Due 2028 |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Redemption price (percent) |  | 100.00% |  |  |  |  |  |  |
U.S. Bank, N.A Credit Agreement | Line of Credit |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Debt instrument, basis spread on variable rate (as a percent) |  |  | 2.25% |  |  |  |  |  |
Outstanding balance on the line of credit |  |  |  | 0 |  |  |  |  |
Maximum borrowing capacity |  |  | $ 75,000,000 |  |  |  |  |  |
Non-refundable facility fee |  |  | 0.40% |  |  |  |  |  |
Putable Advances |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Putable advances with the FHLB |  |  |  | $ 305,000,000.0 |  |  |  |  |
Minimum |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Interest rate, minimum (as a percent) |  |  |  | 1.50% |  |  |  |  |
Maximum |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Interest rate, minimum (as a percent) |  |  |  | 4.94% |  |  |  |  |
Securities Sold Under Repurchase Agreements |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Maximum amount of outstanding agreements |  |  |  | $ 194,200,000 | 242,200,000 |  |  |  |
Total of average agreements |  |  |  | 136,000,000.0 | 171,300,000 |  |  |  |
Debt outstanding |  |  |  | 142,876,000 |  |  |  |  |
Subordinated Debentures and Term Loans |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Debt outstanding |  |  |  | 93,529,000 | 158,600,000 |  |  |  |
Subordinated Debenture | 6.75% Subordinated Notes Due 2028 |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Debt face amount |  | $ 65,000,000 |  |  |  |  |  |  |
Interest rate on notes (as a percent) |  | 6.75% |  |  |  |  |  |  |
Redemption price (percent) |  | 100.00% |  |  |  |  |  |  |
Principal redemption |  |  |  |  |  |  | $ 25,000,000 | $ 40,000,000 |
Subordinated Debenture | Acquired Subordinated Notes |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Debt face amount |  |  |  |  |  |  |  |  | $ 30,000,000
Interest rate on notes (as a percent) |  |  |  |  |  |  |  |  | 4.75%
Debt instrument, basis spread on variable rate (as a percent) | 3.11% |  |  |  |  |  |  |  |
Subordinated Debenture | Acquired Subordinated Notes | Forecast |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Notice of redemption amount |  |  |  |  |  | $ 30,000,000 |  |  |
Subordinated Debenture | First Merchant Capital Trust II |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Debt face amount |  |  |  | $ 41,700,000 | $ 41,700,000 |  |  |  |
Debt instrument, basis spread on variable rate (as a percent) |  |  |  | 26.161% | 26.161% |  |  |  |
Interest rate during the period |  |  |  | 6.18% | 7.21% |  |  |  |
Subordinated Debenture | Ameriana Capital Trust I |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Debt face amount |  |  |  | $ 10,300,000 | $ 10,300,000 |  |  |  |
Debt instrument, basis spread on variable rate (as a percent) |  |  |  | 0.26161% | 0.26161% |  |  |  |
Interest rate during the period |  |  |  | 6.12% | 7.15% |  |  |  |
Senior Notes |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Debt face amount |  | $ 70,000,000 |  |  |  |  |  |  |
Private debt issuance, number of institutional investors | investor |  | 4 |  |  |  |  |  |  |
Senior Notes | 5.00% Senior Notes Due 2028 |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Debt face amount |  | $ 5,000,000 |  |  |  |  |  |  |
Interest rate on notes (as a percent) |  | 5.00% |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage |  |  |  | 7.18% | 7.98% |  |  |  |
Senior Notes | Three-Month SOFR | 5.00% Senior Notes Due 2028 |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Debt instrument, basis spread on variable rate (as a percent) |  |  |  | 0.26161% | 0.26161% |  |  |  |
Senior Notes | SOFR | 5.00% Senior Notes Due 2028 |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Debt instrument, basis spread on variable rate (as a percent) |  |  |  | 2.345% | 2.345% |  |  |  |
Secured Debt |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Debt outstanding |  |  |  | $ 7,100,000 | $ 7,300,000 |  |  |  |
Interest rate on notes (as a percent) |  |  |  | 3.41% | 3.41% |  |  |  |
Secured Debt | Level One |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Debt outstanding |  |  |  | $ 1,100,000 | $ 1,200,000 |  |  |  |
Interest rate on notes (as a percent) |  |  |  | 1.00% | 1.00% |  |  |  |

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- Definition The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -SubTopic 10 -Topic 210 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 942 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1 Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(16)(a)(2)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478777/944-210-S99-1 + Details
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- Definition The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used. + References No definition available. + Details
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- Definition Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)(b)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(19)(b)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1 + Details
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