Acquisitions Allocation of Purchase Price (Details) - USD ($) $ in Thousands			3 Months Ended
	May. 31, 2015	Apr. 01, 2015	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Schedule of Purchase Price Allocation [Line Items]
Goodwill			$ 286,454	$ 180,128	$ 120,164
Short-term borrowings			330,016	389,467	323,086
Other Borrowings			248,396	$ 0	$ 0
Lake Michigan Financial Corp [Member]
Schedule of Purchase Price Allocation [Line Items]
Business Combination, Acquired Receivables, Fair Value	$ 985,500
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Property, Plant, and Equipment			(1,689)
Business Combination, Provisional Information, Initial Accounting Incomplete, Other Assets			(790)
Business Combination, Provisional Information, Initial Accounting Incomplete, Deferred Income Tax Assets			903
Goodwill	100,878
Business Combination, Provision Information, Initial Accounting Incomplete, Goodwill			876
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Intangibles			700
Intangibles acquired	8,000
Business Combination, Consideration Transferred	187,394
Monarch Community Bancorp [Member]
Schedule of Purchase Price Allocation [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents		$ 32,171
Business Combination, Acquired Receivables, Fair Value		121,783
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment		3,064
Business Combination, Deferred Tax Asset, Net Operating Loss		7,900
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Assets Noncurrent		2,383
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables		6,972
Business Combination, Provisional Information, Initial Accounting Incomplete, Deferred Income Tax Assets			100
Goodwill		5,314
Business Combination, Provision Information, Initial Accounting Incomplete, Goodwill			$ (100)
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Mortgage Servicing Rights Asset		1,284
Intangibles acquired		1,930
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets		182,801
Business Combination Deposits Assumed		144,311
Other Borrowings		8,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Other		3,299
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities		155,610
Business Combination, Consideration Transferred		$ 27,191
Original Allocation of Purchase Price [Member] | Lake Michigan Financial Corp [Member]
Schedule of Purchase Price Allocation [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents	39,301
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Marketable Securities	66,699
Business Combination, Acquired Receivables, Fair Value	985,542
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment	13,673
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Assets Noncurrent	14,888
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables	38,449
Goodwill	100,002
Intangibles acquired	7,303
Bank Owned Life Insurance	23,844
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	1,289,701
Business Combination Deposits Assumed	924,697
Short-term borrowings	30,000
Other Borrowings	124,723
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Other	22,887
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities	1,102,307
Business Combination, Consideration Transferred	187,394
Revised Allocation of Purchase Price [Member] [Member] | Lake Michigan Financial Corp [Member]
Schedule of Purchase Price Allocation [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents	39,301
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Marketable Securities	66,699
Business Combination, Acquired Receivables, Fair Value	985,542
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment	11,984
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Assets Noncurrent	15,791
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables	37,659
Goodwill	100,878
Intangibles acquired	8,003
Bank Owned Life Insurance	23,844
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	1,289,701
Business Combination Deposits Assumed	924,697
Short-term borrowings	30,000
Other Borrowings	124,723
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Other	22,887
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities	1,102,307
Business Combination, Consideration Transferred	$ 187,394