v3.25.2
BORROWINGS - Narrative (Details)
6 Months Ended 9 Months Ended 12 Months Ended
Dec. 18, 2024
Nov. 01, 2013
USD ($)
investor
Jun. 30, 2025
USD ($)
Jun. 30, 2024
USD ($)
Sep. 30, 2024
USD ($)
Dec. 31, 2024
USD ($)
Mar. 31, 2025
USD ($)
Dec. 18, 2019
USD ($)
Debt Instrument [Line Items]                
Total available remaining borrowing capacity from FHLB     $ 689,200,000          
Putable advances with the FHLB     898,702,000     $ 822,554,000    
Subordinated debentures and other borrowings     62,617,000     93,529,000    
Debt face amount   $ 70,000,000            
Private debt issuance, number of institutional investors | investor   4            
U.S. Bank, N.A | Line of Credit                
Debt Instrument [Line Items]                
Basis spread on variable rate (as a percent)         2.25%      
Outstanding balance on the line of credit     0     0    
Maximum borrowing capacity         $ 75,000,000      
Non-refundable facility fee         0.40%      
Senior Debt and Subordinated Debt                
Debt Instrument [Line Items]                
Fixed interest rate term   10 years            
Putable Advances                
Debt Instrument [Line Items]                
Putable advances with the FHLB     $ 305,000,000          
Minimum                
Debt Instrument [Line Items]                
Interest rate, minimum (as a percent)     0.00%          
Maximum                
Debt Instrument [Line Items]                
Interest rate, minimum (as a percent)     4.48%          
Securities Sold Under Repurchase Agreements                
Debt Instrument [Line Items]                
Maximum amount of outstanding agreements     $ 169,100,000 $ 194,200,000        
Average balance     141,700,000 144,300,000        
Debt outstanding     114,758,000          
Subordinated Debentures and Term Loans                
Debt Instrument [Line Items]                
Debt outstanding     62,617,000     93,500,000    
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%            
Redeemed     5,000,000 $ 65,000,000        
Subordinated Debenture | Level One Subordinated Notes                
Debt Instrument [Line Items]                
Debt face amount               $ 30,000,000
Basis spread on variable rate (as a percent) 3.11%              
Interest rate on notes (as a percent)               4.75%
Redeemed             $ 30,000,000  
Principal amount outstanding     0          
Subordinated Debenture | First Merchant Capital Trust II                
Debt Instrument [Line Items]                
Debt face amount     $ 41,700,000     $ 41,700,000    
Basis spread on variable rate (as a percent)     0.26161%     0.26161%    
Interest rate during the period     6.14%     6.18%    
Subordinated Debenture | Ameriana Capital Trust I                
Debt Instrument [Line Items]                
Debt face amount     $ 10,300,000     $ 10,300,000    
Basis spread on variable rate (as a percent)     0.26161%     0.26161%    
Interest rate during the period     6.08%     6.12%    
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%            
Senior Notes | First Merchants Senior Notes and Subordinated Notes                
Debt Instrument [Line Items]                
Debt, weighted average interest rate     6.87%     7.18%    
Senior Notes | First Merchants Senior Notes and Subordinated Notes | Secured Overnight Financing Rate (SOFR)                
Debt Instrument [Line Items]                
Basis spread on variable rate (as a percent)     0.26161%     0.26161%    
Senior Notes | First Merchants Senior Notes and Subordinated Notes | Base Rate                
Debt Instrument [Line Items]                
Basis spread on variable rate (as a percent)     2.345%     2.345%    
Secured Debt                
Debt Instrument [Line Items]                
Interest rate on notes (as a percent)     3.41%     3.41%    
Debt outstanding     $ 7,100,000     $ 7,100,000    
Secured Debt | Level One                
Debt Instrument [Line Items]                
Interest rate on notes (as a percent)     1.00%     1.00%    
Debt outstanding     $ 1,100,000     $ 1,100,000