Financing Activities - Other Borrowings (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Proforma Debt Instrument [Line Items]
ASC 815 fair value hedge and other basis adjustments	$ (2,821)
Old National Bancorp [Member]
Proforma Debt Instrument [Line Items]
ASC 815 fair value hedge and other basis adjustments	(3,281)	(3,339)
Old National Bank [Member]
Proforma Debt Instrument [Line Items]
Securities sold under agreements to repurchase (fixed rates 2.47% to 2.50%) maturing January 2017 to January 2018	50,000	50,000
Federal Home Loan Bank advances (fixed rates 0.14% to 8.34% and variable rates 0.32% to 0.36%) maturing October 2013 to January 2023	554,526	155,323
Capital lease obligation	4,170	4,211
ASC 815 fair value hedge and other basis adjustments	460	3,298
Total other borrowings	633,875	237,493
Junior Subordinated Debt [Member] | Old National Bancorp [Member]
Proforma Debt Instrument [Line Items]
Junior subordinated debenture (variable rates of 1.85% to 2.00%) maturing March 2035 to June 2037	$ 28,000	$ 28,000