Parent Company Financial Statements - Condensed Statement of Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash Flows From Operating Activities
Net income	$ 581,992	$ 428,287	$ 277,538
Adjustments to reconcile net income to cash    provided by operating activities:
Depreciation	38,180	36,436	27,276
Share-based compensation expense	27,910	28,656	7,497
(Increase) decrease in other assets	(66,070)	(40,518)	2,641
Increase (decrease) in other liabilities	(79,885)	327,369	17,984
Net cash flows provided by (used in) operating activities	516,342	814,425	330,380
Cash Flows From Investing Activities
Net cash and cash equivalents of acquisitions	0	1,912,629	0
Proceeds from sales of investment securities available-for-sale	96,506	20,032	198,886
Proceeds from sales of equity securities	24,636	53,029	544
Purchases of equity securities	(28,408)	(6,348)	(11,000)
Purchases of investment securities	(1,084,416)	(1,438,572)	(3,321,653)
Purchases of premises and equipment	(38,375)	(37,901)	(48,692)
Net cash flows provided by (used in) investing activities	(1,818,876)	(1,685,507)	(1,431,583)
Cash Flows From Financing Activities
Common stock repurchased	(44,308)	(71,182)	(3,731)
Common stock issued	1,076	809	583
Net cash flows provided by (used in) financing activities	1,749,180	777,475	1,333,510
Net increase (decrease) in cash and cash equivalents	446,646	(93,607)	232,307
Cash and cash equivalents at beginning of period	728,412	822,019	589,712
Cash and cash equivalents at end of period	1,175,058	728,412	822,019
Old National Bancorp
Cash Flows From Operating Activities
Net income	581,992	428,287	277,538
Adjustments to reconcile net income to cash    provided by operating activities:
Depreciation	18	26	30
Share-based compensation expense	27,910	28,656	7,497
(Increase) decrease in other assets	(19,353)	(40,620)	10,213
Increase (decrease) in other liabilities	(2,561)	10,455	(4,918)
Equity in undistributed earnings of affiliates	(481,628)	(470,939)	(166,292)
Net cash flows provided by (used in) operating activities	106,378	(44,135)	124,068
Cash Flows From Investing Activities
Net cash and cash equivalents of acquisitions	0	573,099	0
Proceeds from sales of investment securities available-for-sale	0	0	1,000
Proceeds from sales of equity securities	0	44,038	540
Purchases of equity securities	(17,773)	0	0
Purchases of investment securities	0	(9,000)	(15)
Purchases of premises and equipment	(8)	0	(3)
Net cash flows provided by (used in) investing activities	(17,781)	608,137	1,522
Cash Flows From Financing Activities
Cash dividends paid	(180,030)	(177,623)	(92,829)
Common stock repurchased	(44,308)	(71,182)	(3,731)
Common stock issued	1,076	809	583
Net cash flows provided by (used in) financing activities	(223,262)	(247,996)	(95,977)
Net increase (decrease) in cash and cash equivalents	(134,665)	316,006	29,613
Cash and cash equivalents at beginning of period	418,959	102,953	73,340
Cash and cash equivalents at end of period	$ 284,294	$ 418,959	$ 102,953