Acquisitions (Textual) (Details) $ / shares in Units, $ in Thousands						3 Months Ended	6 Months Ended
	May. 31, 2015 USD ($) Offices $ / shares shares	Apr. 01, 2015 USD ($) Offices shares	Oct. 31, 2014 USD ($) Offices	Dec. 07, 2012 USD ($) Branches	Apr. 30, 2010 USD ($) Offices	Jun. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)	Jun. 30, 2014 USD ($)
Business Acquisition [Line Items]
Goodwill						$ 285,512	$ 285,512	$ 180,128	$ 120,164
Lake Michigan Financial Corp [Member]
Business Acquisition [Line Items]
Expected Principal Cash Flows of Contractually Required Acquired Loan Portfolio	$ 986,100
Expected Interest Cash Flows of Contractually Required Acquired Loan Portfolio	$ 189,600
Business Acquisition, Share Price | $ / shares	$ 16.64
Exchange Ratio of Common Stock Issued, Business Combinations	1.326
Business Combination, Acquired Receivables, Fair Value	$ 985,542
Certain Loans Acquired in Transfer, Nonaccretable Difference	22,600
Acquisition purchase price	$ 187,394
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares | shares	4,322,101
Goodwill	$ 100,002
Purchase Accounting Fair Value Adjustment, Core Deposit Intangible Asset	(7,303)
Intangibles acquired	$ 7,303
Service provided by acquiree bank through number of branches | Offices	5
Assets of acquiree company	$ 1,240,000
Deposits of acquiree company	924,697
Core deposit and other intangible assets acquired in business combination	7,900
Business Combination, Pro Forma Information, Net Interest Income of Acquiree since Acquisition Date						3,200
Business Combination, Pro Forma Information, Noninterest Income of Acquiree since Acquisition Date						300
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual						1,100
Business Combination, Separately Recognized Transactions, Additional Disclosures, Acquisition Cost Expensed						2,000	2,300
Outstanding contractual principal balance of acquired loan portfolio						990,000	990,000
Carrying amount of acquired loan portfolio						967,000	967,000
Business Combination, Acquired Receivables, Gross Contractual Amount	1,010,000
Interest Payments Receivable of Acquired Loan Portfolio	190,200
Business Combination, Acquired Receivables, Estimated Uncollectible	22,000
Business Combination, Consideration Transferred, Value of Stock and Options Issued	132,900
Business Combination, Consideration Transferred, Cash Paid for Outstanding Stock	$ 54,478
Monarch Community Bancorp [Member]
Business Acquisition [Line Items]
Expected Principal Cash Flows of Contractually Required Acquired Loan Portfolio		$ 122,600
Expected Interest Cash Flows of Contractually Required Acquired Loan Portfolio		$ 37,100
Exchange Ratio of Common Stock Issued, Business Combinations		0.0982
Business Combination, Acquired Receivables, Fair Value		$ 121,783
Certain Loans Acquired in Transfer, Nonaccretable Difference		7,100
Acquisition purchase price		$ 27,191
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares | shares		860,575
Goodwill		$ 5,383
Purchase Accounting Fair Value Adjustment, Core Deposit Intangible Asset		(1,930)
Intangibles acquired		$ 1,930
Service provided by acquiree bank through number of branches | Offices		5
Assets of acquiree company		$ 183,000
Deposits of acquiree company		144,311
Business Combination, Separately Recognized Transactions, Additional Disclosures, Acquisition Cost Expensed						1,500	2,300
Outstanding contractual principal balance of acquired loan portfolio						126,000	126,000
Carrying amount of acquired loan portfolio						119,000	119,000
Business Combination, Acquired Receivables, Gross Contractual Amount		128,900
Interest Payments Receivable of Acquired Loan Portfolio		37,800
Business Combination, Acquired Receivables, Estimated Uncollectible		6,300
Business Combination, Consideration Transferred, Cash Paid for Outstanding Stock		203
Operating Loss Carryforwards		22,600
Tax Credit Carryforwards Not Expected to Be Utilized		$ 1,700
Northwestern Bancorp [Member]
Business Acquisition [Line Items]
Expected Principal Cash Flows of Contractually Required Acquired Loan Portfolio			$ 481,000
Expected Interest Cash Flows of Contractually Required Acquired Loan Portfolio			104,000
Business Combination, Acquired Receivables, Fair Value			475,000
Certain Loans Acquired in Transfer, Nonaccretable Difference			34,000
Acquisition purchase price			121,000
Goodwill			60,000
Intangibles acquired			$ 12,900
Service provided by acquiree bank through number of branches | Offices			25
Assets of acquiree company			$ 815,000
Deposits of acquiree company			794,000
Outstanding contractual principal balance of acquired loan portfolio						415,000	415,000	485,000
Carrying amount of acquired loan portfolio						382,000	382,000	452,000
Business Combination, Acquired Receivables, Gross Contractual Amount			507,000
Interest Payments Receivable of Acquired Loan Portfolio			112,000
Business Combination, Acquired Receivables, Estimated Uncollectible			$ 26,000
Independent Bank [Member]
Business Acquisition [Line Items]
Number of branches acquired (branches) | Branches				21
Deposits acquired				$ 404,000
Loans acquired				44,000
Acquisition purchase price				8,100
Premium paid on deposits purchased				$ 11,500
Premium paid as a percentage of deposits purchased (percent)				2.85%
Discount on loans purchased (percent)				1.75%
Goodwill				$ 6,800
Independent Bank [Member] | Core Deposits [Member]
Business Acquisition [Line Items]
Intangibles acquired				$ 5,600
OAK [Member]
Business Acquisition [Line Items]
Loans acquired					$ 627,000
Acquisition purchase price					$ 83,700
Service provided by acquiree bank through number of branches | Offices					14
Assets of acquiree company					$ 820,000
Deposits of acquiree company					693,000
Brokered deposits of acquiree company					193,000
Contractually required principal payments of loan portfolio, acquisition date					683,000
Acquired loan portfolio acquisition date fair value					$ 627,000
Outstanding contractual principal balance of acquired loan portfolio						236,000	236,000	268,000	298,000
Carrying amount of acquired loan portfolio						$ 215,000	$ 215,000	$ 246,000	$ 274,000