Acquisitions (Textual) (Details)							3 Months Ended	6 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	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Business Acquisition [Line Items]
Goodwill							$ 286,867,000	$ 285,512,000	$ 287,393,000
Additions attributable to acquisitions								228,160,000
Talmer Bancorp, Inc. [Member]
Business Acquisition [Line Items]
Business Acquisition, Share Price | $ / shares	$ 1.61
Exchange Ratio of Common Stock Issued, Business Combinations	0.4725
Acquisition purchase price	$ 1,100,000,000
Assets of acquiree company	6,900,000,000
Brokered deposits of acquiree company	389,000,000
Business Combination, Acquired Receivables, Fair Value	$ 5,000,000,000
Service provided by acquiree bank through number of branches | Offices	80
Deposits of acquiree company	$ 5,300,000,000.0
Lake Michigan Financial Corp [Member]
Business Acquisition [Line Items]
Business Acquisition, Share Price | $ / shares		$ 16.64
Exchange Ratio of Common Stock Issued, Business Combinations		1.326
Acquisition purchase price		$ 187,400,000
Assets of acquiree company		1,240,000,000
Business Combination, Acquired Receivables, Gross Contractual Amount		1,010,000,000
Expected Principal Cash Flows of Contractually Required Acquired Loan Portfolio		986,100,000
Expected Interest Cash Flows of Contractually Required Acquired Loan Portfolio		189,600,000
Business Combination, Acquired Receivables, Fair Value		985,500,000
Certain Loans Acquired in Transfer, Nonaccretable Difference		$ 22,600,000
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares | shares		4,322,101
Goodwill		$ 101,000,000
Service provided by acquiree bank through number of branches | Offices		5
Deposits of acquiree company		$ 925,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill		8,600,000
Business Combination, Provision Information, Initial Accounting Incomplete, Goodwill							500,000
Outstanding contractual principal balance of acquired loan portfolio							756,000,000	990,000,000	864,000,000
Carrying amount of acquired loan portfolio							734,000,000	967,000,000	842,000,000
Interest Payments Receivable of Acquired Loan Portfolio		190,200,000
Business Combination, Acquired Receivables, Estimated Uncollectible		22,000,000
Additions attributable to acquisitions		190,200,000						190,246,000
Business Combination, Consideration Transferred, Value of Stock and Options Issued		132,900,000
Business Combination, Consideration Transferred, Cash Paid for Outstanding Stock		$ 54,500,000
Monarch Community Bancorp [Member]
Business Acquisition [Line Items]
Exchange Ratio of Common Stock Issued, Business Combinations			0.0982
Acquisition purchase price			$ 27,200,000
Assets of acquiree company			183,000,000
Purchase Accounting Fair Value Adjustment, Core Deposit Intangible Asset			1,900,000
Business Combination, Acquired Receivables, Gross Contractual Amount			128,900,000
Expected Principal Cash Flows of Contractually Required Acquired Loan Portfolio			122,600,000
Expected Interest Cash Flows of Contractually Required Acquired Loan Portfolio			37,100,000
Business Combination, Acquired Receivables, Fair Value			121,800,000
Certain Loans Acquired in Transfer, Nonaccretable Difference			$ 7,100,000
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares | shares			860,575
Goodwill			$ 5,300,000
Deposits of acquiree company			144,000,000
Outstanding contractual principal balance of acquired loan portfolio							101,000,000	126,000,000	115,000,000
Carrying amount of acquired loan portfolio							94,000,000	119,000,000	108,000,000
Interest Payments Receivable of Acquired Loan Portfolio			37,800,000
Business Combination, Acquired Receivables, Estimated Uncollectible			6,300,000
Additions attributable to acquisitions			$ 37,900,000					37,914,000
Northwestern Bancorp [Member]
Business Acquisition [Line Items]
Acquisition purchase price				$ 121,000,000
Assets of acquiree company				815,000,000
Business Combination, Acquired Receivables, Gross Contractual Amount				507,000,000
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
Business Combination, Acquired Receivables, Fair Value				475,000,000
Certain Loans Acquired in Transfer, Nonaccretable Difference				34,000,000
Goodwill				60,300,000
Intangibles acquired				$ 12,900,000
Service provided by acquiree bank through number of branches | Offices				25
Deposits of acquiree company				$ 794,000,000
Outstanding contractual principal balance of acquired loan portfolio							305,000,000	415,000,000	361,000,000
Carrying amount of acquired loan portfolio							275,000,000	382,000,000	330,000,000
Interest Payments Receivable of Acquired Loan Portfolio				112,000,000
Business Combination, Acquired Receivables, Estimated Uncollectible				26,000,000
Additions attributable to acquisitions				$ 110,000,000				0
Independent Bank [Member]
Business Acquisition [Line Items]
Acquisition purchase price					$ 8,100,000
Loans acquired					44,000,000
Deposits acquired					$ 404,000,000
Number of branches acquired (branches) | Branches					21
Premium paid on deposits purchased					$ 11,500,000
Premium paid as a percentage of deposits purchased (percent)					2.85%
Discount on loans purchased (percent)					1.75%
Goodwill					$ 6,800,000
Independent Bank [Member] | Core deposit intangible assets [Member]
Business Acquisition [Line Items]
Intangibles acquired					$ 5,600,000
OAK [Member]
Business Acquisition [Line Items]
Acquisition purchase price						$ 83,700,000
Assets of acquiree company						820,000,000
Loans acquired						627,000,000
Brokered deposits of acquiree company						$ 193,000,000
Service provided by acquiree bank through number of branches | Offices						14
Deposits of acquiree company						$ 693,000,000
Contractually required principal payments of loan portfolio, acquisition date						683,000,000
Acquired loan portfolio acquisition date fair value						$ 627,000,000
Outstanding contractual principal balance of acquired loan portfolio							182,000,000	236,000,000	204,000,000
Carrying amount of acquired loan portfolio							166,000,000	215,000,000	$ 183,000,000
Additions attributable to acquisitions								$ 0
OAK and Northwestern [Member]
Business Acquisition [Line Items]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield, Reclassifications to Nonaccretable Difference							$ 5,000,000