Financing Activities - Other Borrowings (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended				9 Months Ended	12 Months Ended				9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Aug. 31, 2014 Senior Unsecured Notes [Member]	Sep. 30, 2014 Old National Bancorp [Member]	Dec. 31, 2013 Old National Bancorp [Member]	Sep. 30, 2014 Old National Bancorp [Member] Senior Unsecured Notes [Member]	Sep. 30, 2014 Old National Bancorp [Member] Junior Subordinated Debt [Member]	Dec. 31, 2013 Old National Bancorp [Member] Junior Subordinated Debt [Member]	Sep. 30, 2014 Old National Bank [Member]	Dec. 31, 2013 Old National Bank [Member]
Debt Instrument [Line Items]
Senior unsecured bank notes (fixed rate 4.125%) maturing August 2024				$ 175,000			$ 175,000
Junior subordinated debentures (variable rates of 1.57% to 1.98%) maturing March 2035 to June 2037								45,000	28,000
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 0.15% to 8.34% and variable rates 0.38% to 6.31%) maturing October 2014 to May 2024										602,329	477,856
Capital lease obligation										4,113	4,157
ASC 815 fair value hedge and other basis adjustments	(4,726)				(4,990)	(3,262)				264	(363)
Total other borrowings	$ 871,716	$ 556,388	$ 633,875