Parent Company Financial Statements - Condensed Statements of Income (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income
Net securities gains									$ 5,848	$ 5,718	$ 9,830
Expense
Interest on borrowings	$ 11,932	$ 11,910	$ 10,903	$ 9,686	$ 9,038	$ 8,567	$ 7,867	$ 7,601	44,431	33,073	23,359
Other expenses									28,715	30,974	16,199
Income before income taxes	48,166	45,678	69,934	36,648	43,583	54,064	35,115	30,131	200,426	162,893	141,964
Income tax expense (benefit)	14,710	10,969	30,812	9,671	11,598	16,395	8,959	9,225	66,162	46,177	38,297
Net income	$ 33,456	$ 34,709	$ 39,122	$ 26,977	$ 31,985	$ 37,669	$ 26,156	$ 20,906	134,264	116,716	103,667
Old National Bancorp [Member]
Income
Dividends from affiliates									160,007	67,717	65,292
Net securities gains									100	6	170
Other income									40,841	1,892	1,554
Other income from affiliates									6	51	79
Total income									200,954	69,666	67,095
Expense
Interest on borrowings									9,077	8,684	3,837
Other expenses									18,460	13,957	11,357
Total expense									27,537	22,641	15,194
Income before income taxes									173,417	47,025	51,901
Income tax expense (benefit)									11,952	(5,473)	(4,020)
Income before equity in undistributed earnings of affiliates									161,465	52,498	55,921
Equity in undistributed earnings of affiliates									(27,201)	64,218	47,746
Net income									$ 134,264	$ 116,716	$ 103,667