Other Borrowings - Additional Information (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Dec. 31, 2022	Feb. 15, 2022	Oct. 29, 2020
Debt Instrument [Line Items]
Other borrowings	$ 21,595	$ 13,469
Old National Bank
Debt Instrument [Line Items]
Other borrowings	21,595	13,469
Subordinated Debt | Old National Bank
Debt Instrument [Line Items]
Subordinated debentures	12,000	12,000
Subordinated Debt | Old National Bancorp
Debt Instrument [Line Items]
Subordinated debentures	$ 150,000	$ 150,000
Fixed rate (in percent)	5.875%
Anchor Bank (MN) | Subordinated Debentures | Subordinated Fixed-to-Floating Notes
Debt Instrument [Line Items]
Value of subordinated fixed-to-floating notes assumed				$ 12,000
Anchor Bank (MN) | Subordinated Debentures | Subordinated Fixed-to-Floating Notes | Secured Overnight Financing Rate (SOFR)
Debt Instrument [Line Items]
Variable rate (in percent)	4.618%
First Midwest
Debt Instrument [Line Items]
Subordinated debentures			$ 150,000