Stock-Based Compensation - Additional Information (Detail) (USD $)		9 Months Ended						9 Months Ended								1 Months Ended
	Sep. 30, 2014	Sep. 30, 2014 Stock Options [Member]	Sep. 30, 2013 Stock Options [Member]	Apr. 25, 2014 Stock Options [Member] Tower Financial Corporation [Member]	Jul. 31, 2014 Stock Options [Member] United Bancorp, Inc. [Member]	Jul. 31, 2014 Stock Options [Member] Old National Bancorp [Member]	Apr. 25, 2014 Stock Options [Member] Old National Bancorp [Member]	Sep. 30, 2014 Restricted Stock [Member]	Sep. 30, 2013 Restricted Stock [Member]	Sep. 30, 2014 Restricted Stock [Member] Minimum [Member]	Sep. 30, 2014 Restricted Stock [Member] Maximum [Member]	Sep. 30, 2014 Restricted Stock Units [Member]	Sep. 30, 2013 Restricted Stock Units [Member]	Sep. 30, 2014 Stock Appreciation Rights (SARs) [Member]	Sep. 30, 2013 Stock Appreciation Rights (SARs) [Member]	Jul. 31, 2014 Stock Appreciation Rights (SARs) [Member] United Bancorp, Inc. [Member]	Jul. 31, 2014 Stock Appreciation Rights (SARs) [Member] Old National Bancorp [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining shares available for issuance	5,200,000
Shares granted during period								194,000				260,000				183,000	163,000
Share-based compensation awards, vesting period										36 months	60 months	36 months
Unrecognized compensation expense								$ 2,800,000				$ 3,500,000
Stock based compensation expense		0	0					700,000	500,000			1,000,000	1,400,000	0	0
Stock based compensation reversal expense												700,000
Options converted				22,000	260,000	231,000	37,000
Incremental expense associated with conversion of stock appreciation rights																	$ 0