v3.26.1
OTHER BORROWINGS - Schedule of Other Borrowings (Details) - USD ($)
$ in Thousands
6 Months Ended 12 Months Ended
Jun. 30, 2026
Dec. 31, 2025
Debt Instrument [Line Items]    
Finance lease liabilities $ 20,290 $ 25,798
Total other borrowings 1,387,997 852,429
Old National Bank    
Debt Instrument [Line Items]    
Other basis adjustments 72,819 10,789
Finance lease liabilities 20,290 25,798
Derivative collateralize position amount 72,800 10,800
Leveraged Loans for NMTC | Old National Bank    
Debt Instrument [Line Items]    
Leveraged loans for NMTC (fixed rates of 1.00% to 7.25%) maturing December 2027 to June 2061 $ 495,395 459,452
Leveraged Loans for NMTC | Minimum | Old National Bank    
Debt Instrument [Line Items]    
Fixed rates 1.00%  
Leveraged Loans for NMTC | Maximum | Old National Bank    
Debt Instrument [Line Items]    
Fixed rates 7.25%  
Old National Bancorp    
Debt Instrument [Line Items]    
Other basis adjustments $ 5,312 7,891
Old National Bancorp | Subordinated Debt    
Debt Instrument [Line Items]    
Subordinated debentures 600,000 150,000
Unamortized debt issuance costs related to subordinated debentures $ (4,318) 0
Old National Bancorp | Subordinated Debt | Minimum    
Debt Instrument [Line Items]    
Fixed rates 5.77%  
Old National Bancorp | Subordinated Debt | Maximum    
Debt Instrument [Line Items]    
Fixed rates 5.88%  
Old National Bancorp | Junior Subordinated Debentures    
Debt Instrument [Line Items]    
Junior subordinated debentures (rates of 5.33% to 7.51%) maturing July 2031 to September 2037 $ 198,499 $ 198,499
Old National Bancorp | Junior Subordinated Debentures | Minimum    
Debt Instrument [Line Items]    
Variable rates 5.33%  
Old National Bancorp | Junior Subordinated Debentures | Maximum    
Debt Instrument [Line Items]    
Variable rates 7.51%