Acquisitions (Textual) (Details) $ / shares in Units, $ in Thousands							3 Months Ended	12 Months Ended
	Jan. 25, 2016 USD ($) Offices $ / shares	May. 31, 2015 USD ($) Offices $ / shares shares	Apr. 01, 2015 USD ($) shares	Oct. 31, 2014 USD ($) Offices	Dec. 07, 2012 USD ($) Branches	Apr. 30, 2010 USD ($) Offices	Dec. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Business Acquisition [Line Items]
Goodwill							$ 287,393	$ 287,393	$ 180,128
Accretable yield								228,160	110,003
Monarch Community Bancorp [Member]
Business Acquisition [Line Items]
Common stock exchange ratio			0.0982
Acquisition purchase price			$ 27,191
Acquisition-related transaction expenses								2,300
Goodwill			5,330
Intangibles acquired			1,930
Assets of acquiree company			183,000
Fair value of loans acquired in acquisition			121,783
Deposits of acquiree company			144,311
Contractually required principal and interest payments of loan portfolio			128,900
Contractually required interest payments of loan portfolio			37,800
Expected principal cash flows of contractually required acquired loan portfolio			122,600
Expected interest cash flows of contractually required acquired loan portfolio			37,100
Nonaccretable difference			7,100
Expected credit losses			6,300
Accretable yield			37,900					37,914
Outstanding contractual principal balance of acquired loan portfolio							115,000	115,000
Carrying amount of acquired loan portfolio							108,000	108,000
Business Combination, Consideration Transferred, Cash Paid for Outstanding Stock			$ 203
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares | shares			860,575
Lake Michigan Financial Corp [Member]
Business Acquisition [Line Items]
Common stock exchange ratio		1.326
Acquisition purchase price		$ 187,394
Cash purchase price per share | $ / shares		$ 16.64
Acquisition-related transaction expenses								5,500
Goodwill		$ 101,621
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill		$ 8,600
Service provided by acquiree bank through number of branches | Offices		5
Assets of acquiree company		$ 1,240,000
Fair value of loans acquired in acquisition		985,500
Deposits of acquiree company		925,000
Contractually required principal and interest payments of loan portfolio		1,010,000
Contractually required interest payments of loan portfolio		190,200
Expected principal cash flows of contractually required acquired loan portfolio		986,100
Expected interest cash flows of contractually required acquired loan portfolio		189,600
Nonaccretable difference		22,600
Expected credit losses		22,000
Accretable yield		190,200						190,246
Outstanding contractual principal balance of acquired loan portfolio							864,000	864,000
Carrying amount of acquired loan portfolio							842,000	842,000
Business Combination, Consideration Transferred, Value of Stock and Options Issued		132,900
Business Combination, Consideration Transferred, Cash Paid for Outstanding Stock		$ 54,478
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares | shares		4,300,000
Business Combination, Provision Information, Initial Accounting Incomplete, Goodwill							700
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Property, Plant, and Equipment							1,000
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Intangibles							100
Business Combination, Provisional Information, Initial Accounting Incomplete, Deferred Income Tax Assets							400
Northwestern Bancorp [Member]
Business Acquisition [Line Items]
Acquisition purchase price				$ 121,000
Acquisition-related transaction expenses									5,800
Goodwill				60,000			60,300	60,300
Intangibles acquired				$ 12,891
Service provided by acquiree bank through number of branches | Offices				25
Assets of acquiree company				$ 815,000
Fair value of loans acquired in acquisition				475,000
Deposits of acquiree company				794,000
Contractually required principal and interest payments of loan portfolio				507,000
Contractually required interest payments of loan portfolio				112,000
Expected principal cash flows of contractually required acquired loan portfolio				481,000
Expected interest cash flows of contractually required acquired loan portfolio				104,000
Nonaccretable difference				34,000
Expected credit losses				$ 26,000
Accretable yield								0	110,003
Outstanding contractual principal balance of acquired loan portfolio							361,000	361,000	485,000
Carrying amount of acquired loan portfolio							330,000	330,000	452,000
Business Combination, Provision Information, Initial Accounting Incomplete, Goodwill							200	300
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Property, Plant, and Equipment							300
Business Combination, Provisional Information, Initial Accounting Incomplete, Deferred Income Tax Assets							100
Independent Bank [Member]
Business Acquisition [Line Items]
Acquisition purchase price					$ 8,100
Number of branches acquired (branches) | Branches					21
Deposits acquired					$ 404,000
Loans acquired					44,000
Premium paid on deposits purchased					$ 11,500
Premium paid as a percent of deposits purchased (percent)					2.85%
Discount on loans purchased (percent)					1.75%
Goodwill					$ 6,800
Intangibles acquired					5,600
OAK [Member]
Business Acquisition [Line Items]
Acquisition purchase price						$ 83,700
Goodwill						43,500
Intangibles acquired						$ 9,800
Service provided by acquiree bank through number of branches | Offices						14
Assets of acquiree company						$ 820,000
Fair value of loans acquired in acquisition						627,000
Deposits of acquiree company						693,000
Brokered deposits of acquiree company						$ 193,000
Accretable yield								0	0
Outstanding contractual principal balance of acquired loan portfolio							204,000	204,000	268,000
Carrying amount of acquired loan portfolio							$ 183,000	$ 183,000	246,000
Reclassification from nonaccretable difference									$ 10,000
Core deposit intangible assets [Member] | Independent Bank [Member]
Business Acquisition [Line Items]
Intangibles acquired					$ 5,600
Talmer Bancorp, Inc. [Member] | Talmer Bancorp, Inc. [Member]
Business Acquisition [Line Items]
Common stock exchange ratio	0.4725
Acquisition purchase price	$ 1,100,000
Cash purchase price per share | $ / shares	$ 1.61
Service provided by acquiree bank through number of branches | Offices	81
Assets of acquiree company	$ 6,600,000
Fair value of loans acquired in acquisition	4,800,000
Deposits of acquiree company	5,000,000
Brokered deposits of acquiree company	$ 229,000