Other Borrowings - Summary of Other Borrowings (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2024	Dec. 31, 2023
Debt Instrument [Line Items]
Finance lease liabilities	$ 33,598	$ 20,955
Other borrowings	598,054	764,870
Old National Bank
Debt Instrument [Line Items]
Other basis adjustments	35,455	97,872
Finance lease liabilities	33,598	20,955
Derivative collateralize position amount	$ 35,400	97,600
Subordinated Debt \| Old National Bank
Debt Instrument [Line Items]
Variable rates	9.87%
Variable rate	4.618%
Subordinated debentures	$ 12,000	12,000
Leveraged Loans for NMTC \| Old National Bank
Debt Instrument [Line Items]
Leveraged loans for NMTC (fixed rates of 1.00% to 1.43%) maturing December 2046 to June 2060	$ 186,020	154,284
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	1.43%
Old National Bancorp
Debt Instrument [Line Items]
Other basis adjustments	$ 14,338	18,207
Old National Bancorp \| Subordinated Debt \| Subordinated Debentures, Due September 2026
Debt Instrument [Line Items]
Fixed rates	5.88%
Subordinated debentures	$ 150,000	150,000
Old National Bancorp \| Subordinated Debt \| Subordinated Debt Due on June 2030
Debt Instrument [Line Items]
Fixed rates	5.25%
Subordinated debentures	$ 30,000	0
Old National Bancorp \| Junior Subordinated Debentures
Debt Instrument [Line Items]
Junior subordinated debentures (rates of 6.42% to 9.09%) maturing July 2031 to September 2037	$ 136,643	136,643
Old National Bancorp \| Junior Subordinated Debentures \| Minimum
Debt Instrument [Line Items]
Variable rates	6.42%
Old National Bancorp \| Junior Subordinated Debentures \| Maximum
Debt Instrument [Line Items]
Variable rates	9.09%
Old National Bancorp \| Senior Unsecured Notes
Debt Instrument [Line Items]
Fixed rates	4.13%
Senior unsecured notes (fixed rate 4.13%) matured August 2024	$ 0	175,000
Unamortized debt issuance costs related to senior unsecured notes	$ 0	$ (91)

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