Business Combination - Narrative (Details) (USD $) Share data in Millions, unless otherwise specified	3 Months Ended		6 Months Ended		0 Months Ended	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Nov. 12, 2013 Merger with CFS Bancorp, Inc. (Citizens)	Jun. 30, 2014 Merger with CFS Bancorp, Inc. (Citizens)	Nov. 12, 2013 Merger with CFS Bancorp, Inc. (Citizens) bank	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					$ 135,600,000
Core deposit intangible							7,313,000
Acquired intangible asset, expected useful life					10 years
Acquisition integration expenses						1,600,000
Salary and employee benefits expense	23,430,000	20,536,000	48,731,000	41,327,000		521,000
Equipment expenses	2,096,000	1,742,000	4,835,000	3,516,000		619,000
Marketing expenses	$ 789,000	$ 535,000	$ 1,558,000	$ 1,002,000		$ 125,000