Other Borrowings - Summary of Other Borrowings (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Lease liability	$ 21,595	$ 13,469
Other borrowings	863,455	743,003
Old National Bank
Debt Instrument [Line Items]
Other basis adjustments	205,106	89,588
Lease liability	21,595	13,469
Derivative collateralize position amount	204,500	88,000
Old National Bancorp
Debt Instrument [Line Items]
Other basis adjustments	$ 19,496	23,363
Senior Unsecured Notes \| Old National Bancorp
Debt Instrument [Line Items]
Fixed rate (in percent)	4.125%
Senior unsecured notes (fixed rate 4.125%) maturing August 2024	$ 175,000	175,000
Unamortized debt issuance costs related to senior unsecured notes	$ (130)	(247)
Subordinated Debt \| Old National Bank
Debt Instrument [Line Items]
Variable rate (in percent)	9.99%
Subordinated debentures	$ 12,000	12,000
Subordinated Debt \| Old National Bancorp
Debt Instrument [Line Items]
Fixed rate (in percent)	5.875%
Subordinated debentures	$ 150,000	150,000
Junior Subordinated Debentures \| Old National Bancorp
Debt Instrument [Line Items]
Junior subordinated debentures (rates of 6.95% to 9.21%) maturing July 2031 to September 2037	136,643	136,643
Notes Payable to Banks \| 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	$ 143,745	$ 143,187
Minimum \| Junior Subordinated Debentures \| Old National Bancorp
Debt Instrument [Line Items]
Variable rate (in percent)	6.95%
Minimum \| Notes Payable to Banks \| Old National Bank
Debt Instrument [Line Items]
Fixed rate (in percent)	1.00%
Maximum \| Junior Subordinated Debentures \| Old National Bancorp
Debt Instrument [Line Items]
Variable rate (in percent)	9.21%
Maximum \| Notes Payable to Banks \| Old National Bank
Debt Instrument [Line Items]
Fixed rate (in percent)	1.43%

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