Goodwill (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)	May. 31, 2015 USD ($)	Apr. 01, 2015 USD ($)	Dec. 31, 2014 USD ($)	Oct. 31, 2014 USD ($)	Dec. 07, 2012 USD ($) Branches
Goodwill [Line Items]
Goodwill	$ 287,393	$ 287,393			$ 180,128
Lake Michigan Financial Corp [Member]
Goodwill [Line Items]
Goodwill			$ 101,621
Business Combination, Provision Information, Initial Accounting Incomplete, Goodwill	700
Monarch Community Bancorp [Member]
Goodwill [Line Items]
Goodwill				$ 5,330
Northwestern Bancorp [Member]
Goodwill [Line Items]
Goodwill	60,300	60,300				$ 60,000
Business Combination, Provision Information, Initial Accounting Incomplete, Goodwill	$ 200	$ 300
Independent Bank [Member]
Goodwill [Line Items]
Goodwill							$ 6,800
Number of branches acquired (branches) | Branches							21