Business Combination - Narrative (Details) (USD $) Share data in Millions, unless otherwise specified	3 Months Ended		0 Months Ended	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Nov. 12, 2013 Merger with CFS Bancorp, Inc. (Citizens) bank	Mar. 31, 2014 Merger with CFS Bancorp, Inc. (Citizens)	Nov. 12, 2013 Merger with CFS Bancorp, Inc. (Citizens) CFS Bancorp [Member]
Business Acquisition [Line Items]
Percentage of Interest Acquired			100.00%
Number of full service banking centers owned			20
Percentage of common stock received per shares owned through acquisition					0.65%
Core deposit intangible			7.1
Value of stock issued as a part of acquisition			$ 135,642,000
Core deposit intangible			7,313,000
Acquired intangible asset, expected useful life			10 years
Acquisition integration expenses				1,400,000
Salary and employee benefits expense	25,301,000	20,791,000		523,000
Equipment expenses	2,739,000	1,774,000		480,000
Marketing expenses	$ 769,000	$ 467,000		$ 122,000