Other Borrowings - Summary of Other Borrowings (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
Jun. 30, 2024	Dec. 31, 2023
Debt Instrument [Line Items]
Finance lease liabilities	$ 34,114	$ 20,955
Other borrowings	849,777	764,870
Old National Bank
Debt Instrument [Line Items]
Other basis adjustments	128,178	97,872
Finance lease liabilities	34,114	20,955
Derivative collateralize position amount	128,100	97,600
Old National Bancorp
Debt Instrument [Line Items]
Other basis adjustments	$ 15,627	18,207
Senior Unsecured Notes \| Old National Bancorp
Debt Instrument [Line Items]
Fixed rates	4.13%
Senior unsecured notes (fixed rate 4.13%) maturing August 2024	$ 175,000	175,000
Unamortized debt issuance costs related to senior unsecured notes	$ (13)	(91)
Subordinated Debt \| Old National Bank
Debt Instrument [Line Items]
Variable rates	9.95%
Variable rate	4.618%
Subordinated debentures	$ 12,000	12,000
Subordinated Debt \| Old National Bancorp
Debt Instrument [Line Items]
Fixed rates	5.88%
Subordinated debentures	$ 150,000	150,000
Subordinated Debt \| Old National Bancorp \| Subordinated Debt Due on June 2030
Debt Instrument [Line Items]
Fixed rates	5.25%
Subordinated debentures	$ 30,000	0
Junior Subordinated Debentures \| Old National Bancorp
Debt Instrument [Line Items]
Junior subordinated debentures (rates of 6.95% to 9.17%) maturing July 2031 to September 2037	136,643	136,643
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	$ 168,228	$ 154,284
Minimum \| Junior Subordinated Debentures \| Old National Bancorp
Debt Instrument [Line Items]
Variable rates	6.95%
Minimum \| Leveraged Loans for NMTC \| Old National Bank
Debt Instrument [Line Items]
Fixed rates	1.00%
Maximum \| Junior Subordinated Debentures \| Old National Bancorp
Debt Instrument [Line Items]
Variable rates	9.17%
Maximum \| Leveraged Loans for NMTC \| Old National Bank
Debt Instrument [Line Items]
Fixed rates	1.43%

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