Goodwill and Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Goodwill and Intangible Assets Gross Carrying Value [Abstract]
Goodwill not subject to amortization		$ 44,767	$ 29,513
Intangibles from branch acquisition		3,015	3,015
Core deposit intangibles		15,202	8,986
Customer list intangibles		3,731	1,904
Total Goodwill and Intangible Assets, Gross Carrying Value		66,715	43,418
Goodwill and Intangible Assets Accumulated Amortization [Abstract]
Goodwill not subject to amortization (effective 1/1/02), Accumulated Amortization		3,760	3,760
Total Goodwill and Intangible Assets, Accumulated Amortization		16,711	15,821
Total Amortization Expense [Abstract]
Amortization of intangible assets		891	643	$ 674
Estimated amortization expense [Abstract]
For year ended 12/31/16		1,572
For year ended 12/31/17		1,322
For year ended 12/31/18		1,193
For year ended 12/31/19		1,079
For year ended 12/31/20		933
OldNationalBankBranches [Member]
Goodwill and Intangible Assets Accumulated Amortization [Abstract]
Goodwill, Acquired During Period	$ 14,300	14,274
Illiana [Member]
Goodwill and Intangible Assets Accumulated Amortization [Abstract]
Goodwill, Acquired During Period		980
Intangibles from branch acquisitions
Goodwill and Intangible Assets Accumulated Amortization [Abstract]
Intangible Assets, Accumulated Amortization		3,015	3,015
Core deposit intangibles
Goodwill and Intangible Assets Accumulated Amortization [Abstract]
Intangible Assets, Accumulated Amortization		8,017	7,142
Total Amortization Expense [Abstract]
Amortization of intangible assets		876	643	674
Customer list intangibles
Goodwill and Intangible Assets Accumulated Amortization [Abstract]
Intangible Assets, Accumulated Amortization		1,919	1,904
Total Amortization Expense [Abstract]
Amortization of intangible assets		$ 15	$ 0	$ 0