Acquisitions Unaudited Pro Forma Information (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Business Acquisition [Line Items]
Business Acquisition, Pro Forma interest and dividend income	$ 78,137	$ 74,842	$ 154,261	$ 148,089
Business Acquisition, Pro Forma interest expense	5,483	6,748	11,363	13,627
Business Acquisition, Pro Forma net interest income	72,654	68,094	142,898	134,462
Business Acquisition, Pro Forma provision for loan losses	1,500	1,860	3,000	4,035
Business Acquisition, Pro Forma net interest income after provision for loan losses	71,154	66,234	139,898	130,427
Business Acquisition, Pro Forma noninterest income	21,153	23,713	43,180	43,487
Business Acquisition, Pro Forma noninterest expense	62,394	59,915	123,042	121,241
Business Acquisition, Pro Forma pre-tax net income	29,913	30,032	60,036	52,673
Business Acquisition, Pro Forma federal income tax expense	7,525	9,048	16,736	15,807
Business Acquisition, Pro Forma Net Income (Loss)	$ 22,388	$ 20,984	$ 43,300	$ 36,866
Business Acquisition, Pro Forma Earnings Per Share, Basic	$ 0.59	$ 0.60	$ 1.14	$ 1.05
Business Acquisition, Pro Forma Earnings Per Share, Diluted	$ 0.58	$ 0.59	$ 1.13	$ 1.04
Weighted Average Number of Shares Outstanding, Basic	35,162	30,068	33,992	29,947
Weighted Average Number of Shares Outstanding, Diluted	35,397	30,279	34,227	30,159
Lake Michigan, Monarch and Northwestern [Member]
Business Acquisition [Line Items]
Weighted Average Number of Shares Outstanding, Basic	38,044	35,251	38,024	35,129
Weighted Average Number of Shares Outstanding, Diluted	38,279	35,462	38,259	35,398