Acquisitions Unaudited Pro Forma Information (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Business Acquisition [Line Items]
Business Acquisition, Pro Forma interest and dividend income	$ 78,851	$ 76,651	$ 233,136	$ 224,740
Business Acquisition, Pro Forma interest expense	5,234	6,526	16,596	20,152
Business Acquisition, Pro Forma net interest income	73,617	70,125	216,540	204,588
Business Acquisition, Pro Forma provision for loan losses	1,500	1,950	4,500	5,985
Business Acquisition, Pro Forma net interest income after provision for loan losses	72,117	68,175	212,040	198,603
Business Acquisition, Pro Forma noninterest income	20,215	22,209	63,395	65,696
Business Acquisition, Pro Forma noninterest expense	57,365	60,863	180,147	183,084
Business Acquisition, Pro Forma pre-tax net income	34,967	29,521	95,288	81,215
Business Acquisition, Pro Forma federal income tax expense	9,915	8,569	21,192	24,011
Business Acquisition, Pro Forma Net Income (Loss)	$ 25,052	$ 20,952	$ 74,096	$ 57,204
Business Acquisition, Pro Forma Earnings Per Share, Basic	$ 0.66	$ 0.55	$ 1.95	$ 1.59
Business Acquisition, Pro Forma Earnings Per Share, Diluted	$ 0.65	$ 0.55	$ 1.93	$ 1.58
Weighted Average Number of Shares Outstanding, Basic	38,123	32,762	35,384	30,896
Weighted Average Number of Shares Outstanding, Diluted	38,393	32,956	35,630	31,101
Lake Michigan, Monarch and Northwestern [Member]
Business Acquisition [Line Items]
Weighted Average Number of Shares Outstanding, Basic	38,123	37,944	38,072	36,071
Weighted Average Number of Shares Outstanding, Diluted	38,393	38,139	38,319	36,307