Parent Company Financial Statements - Condensed Balance Sheets (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Assets
Equity securities	$ 6,842	$ 5,582
Available-for-Sale securities, Fair Value	5,385,091	4,123,416
Other assets	196,831	185,197
Total assets	20,411,667	19,728,435
Liabilities and Shareholders' Equity
Other borrowings	243,685	247,883
Shareholders' equity	2,852,453	2,689,570	$ 2,154,397	$ 1,814,417
Total liabilities and shareholders' equity	20,411,667	19,728,435
Old National Bancorp [Member]
Assets
Deposits in affiliate bank	41,289	90,005
Equity securities	6,724	5,582
Available-for-Sale securities, Fair Value	4,018	1,527
Investment in affiliates, Banking subsidiaries	2,966,575	2,769,166
Investment in affiliates, Non-banks	4,885	5,151
Other assets	89,093	87,096
Total assets	3,112,584	2,958,527
Liabilities and Shareholders' Equity
Other liabilities	36,369	37,563
Other borrowings	223,762	231,394
Shareholders' equity	2,852,453	2,689,570
Total liabilities and shareholders' equity	$ 3,112,584	$ 2,958,527