Business Combination - Pro Forma Information (Details) (Merger with CFS Bancorp, Inc. (Citizens), USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Merger with CFS Bancorp, Inc. (Citizens)
Business Acquisition [Line Items]
Total revenue (net interest income plus other income)	$ 243,972	$ 266,034
Net income	38,637	50,092
Net income available to common shareholders	$ 36,257	$ 45,553
Earnings per share:
Basic (in dollars per share)	$ 0.98	$ 1.28
Diluted (in dollars per share)	$ 0.98	$ 1.27