Acquisitions (Textual) (Details) (USD $)	12 Months Ended		0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Oct. 31, 2014	Dec. 07, 2012 Branches	Apr. 30, 2010 Offices	Jan. 05, 2015
Business Acquisition [Line Items]
Goodwill	$ 180,128,000	$ 120,164,000
Accretable yield	110,003,000	0
Reclassification from nonaccretable difference	10,000,000	125,000
Monarch Community Bancorp [Member]
Business Acquisition [Line Items]
Common stock exchange ratio			0.0982
Acquisition purchase price			27,000,000
Northwestern Bancorp [Member]
Business Acquisition [Line Items]
Acquisition purchase price			121,008,000
Acquisition-related transaction expenses	5,800,000
Goodwill			59,964,000
Intangibles acquired			12,891,000
Service provided by acquiree bank through number of branches			25
Assets of acquiree company			815,000,000
Fair value of loans acquired in acquisition			475,285,000
Deposits of acquiree company			794,447,000
Contractually required principal and interest payments of loan portfolio			507,000,000
Contractually required interest payments of loan portfolio			112,000,000
Expected principal cash flows of contractually required acquired loan portfolio			481,000,000
Expected interest cash flows of contractually required acquired loan portfolio			104,000,000
Nonaccretable difference			34,000,000
Expected credit losses			26,000,000
Accretable yield	110,003,000
Outstanding contractual principal balance of acquired loan portfolio	485,000,000
Carrying amount of acquired loan portfolio	452,000,000
Reclassification from nonaccretable difference	0
Independent Bank [Member]
Business Acquisition [Line Items]
Acquisition purchase price				8,100,000
Number of branches acquired (branches)				21
Deposits acquired				404,000,000
Loans acquired				44,000,000
Premium paid on deposits purchased				11,500,000
Premium paid as a percent of deposits purchased (percent)				2.85%
Discount on loans purchased (percent)				1.75%
Goodwill				6,800,000
Intangibles acquired				5,600,000
OAK [Member]
Business Acquisition [Line Items]
Acquisition purchase price					83,700,000
Goodwill					43,500,000
Intangibles acquired					9,800,000
Service provided by acquiree bank through number of branches					14
Assets of acquiree company					820,000,000
Fair value of loans acquired in acquisition					627,000,000
Deposits of acquiree company					693,000,000
Brokered deposits of acquiree company					193,000,000
Accretable yield	0	0
Outstanding contractual principal balance of acquired loan portfolio	268,000,000	320,000,000
Carrying amount of acquired loan portfolio	246,000,000	295,000,000
Reclassification from nonaccretable difference	10,000,000	125,000
Core deposit intangible assets [Member] | Independent Bank [Member]
Business Acquisition [Line Items]
Intangibles acquired				5,600,000
Lake Michigan Financial Corp [Member] | Lake Michigan Financial Corp [Member]
Business Acquisition [Line Items]
Common stock exchange ratio						1.326
Acquisition purchase price						$ 184,100,000
Cash purchase price per share						$ 16.64