Business Combinations (Narrative) (Details) (USD $)	12 Months Ended		0 Months Ended								24 Months Ended	36 Months Ended	0 Months Ended			12 Months Ended	0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Feb. 01, 2013	Jul. 11, 2014	May 16, 2014	Oct. 18, 2013 locations	May 01, 2013	Dec. 12, 2012 locations	Apr. 13, 2012	Mar. 30, 2012	Dec. 31, 2011 financial_institution	Dec. 31, 2014 segment	Apr. 28, 2014	Jun. 08, 2012	Oct. 02, 2013	Sep. 30, 2013 locations	Aug. 08, 2014 locations
Business Acquisition [Line Items]
Additional goodwill recorded on acquisition	$ 33,234,000
FDIC loss sharing percentage on purchased loans, OREO, and certain other assets		80.00%
Second Federal [Member]
Business Acquisition [Line Items]
Disposal Date			Feb. 01, 2013
Divestiture of Businesses, Deposits Disposed			149,000,000
THE National Bank [Member]
Business Acquisition [Line Items]
Date of acquisition				Jul. 11, 2014
Fair value of assets acquired, at the acquisition date				94,100,000
Fair value of loans acquired, at the acquisition date				75,000,000
Fair value of deposits				36,200,000
Additional goodwill recorded on acquisition				16,300,000
Urban Partnership Bank, Stone Park Branch [Member]
Business Acquisition [Line Items]
Date of acquisition					May 16, 2014
Fair value of liabilities assumed, at the acquisition date					5,500,000
Fair value of deposits					5,400,000
Additional goodwill recorded on acquisition					678,000
Diamond Bancorp, Inc [Member]
Business Acquisition [Line Items]
Date of acquisition						Oct. 18, 2013
Number of Locations						4
Fair value of assets acquired, at the acquisition date						172,500,000
Fair value of loans acquired, at the acquisition date						91,700,000
Fair value of liabilities assumed, at the acquisition date						169,100,000
Fair value of deposits						140,200,000
Additional goodwill recorded on acquisition						8,400,000
First Lansing Bancorp, Inc. [Member]
Business Acquisition [Line Items]
Date of acquisition							May 01, 2013
Fair value of assets acquired, at the acquisition date							373,400,000
Fair value of loans acquired, at the acquisition date							123,000,000
Fair value of liabilities assumed, at the acquisition date							334,700,000
Fair value of deposits							331,400,000
Additional goodwill recorded on acquisition							14,000,000
First Lansing Bancorp, Inc. [Member] | South and Southwest Suburbs of Chicago, Illinois [Member]
Business Acquisition [Line Items]
Number of Locations							7
First Lansing Bancorp, Inc. [Member] | Northwest Indiana [Member]
Business Acquisition [Line Items]
Number of Locations							1
HPK Financial Corporation [Member]
Business Acquisition [Line Items]
Date of acquisition								Dec. 12, 2012
Number of Locations								2
Fair value of assets acquired, at the acquisition date								371,600,000
Fair value of loans acquired, at the acquisition date								118,500,000
Fair value of liabilities assumed, at the acquisition date								344,100,000
Fair value of deposits								243,800,000
Additional goodwill recorded on acquisition								12,600,000
Suburban Bank And Trust Company [Member]
Business Acquisition [Line Items]
Date of acquisition									Apr. 13, 2012	Mar. 30, 2012
Fair value of loans acquired, at the acquisition date									3,000,000
Fair value of deposits									52,000,000
Additional goodwill recorded on acquisition									1,500,000	1,800,000
Assets under management, carrying amount										160,000,000
FDIC Assisted [Member]
Business Acquisition [Line Items]
Number of FDIC-assisted banks acquired											6	3
Policy Billing Services Inc. And Equity Premium Finance Inc. [Member]
Business Acquisition [Line Items]
Date of acquisition													Apr. 28, 2014
Fair value of loans acquired, at the acquisition date													7,400,000
Additional goodwill recorded on acquisition													6,500,000
Number of Affiliated Companies Acquired													2
Macquarie Premium Funding Inc [Member]
Business Acquisition [Line Items]
Date of acquisition														Jun. 08, 2012
Fair value of loans acquired, at the acquisition date														213,000,000
Additional goodwill recorded on acquisition														21,900,000
Surety Financial Services [Member]
Business Acquisition [Line Items]
Date of acquisition															Oct. 01, 2013
Number of Locations																5
Additional goodwill recorded on acquisition															9,500,000
Mortgage Loan Originations																1,000,000,000
Community Banking [Member]
Business Acquisition [Line Items]
Additional goodwill recorded on acquisition	26,439,000
Community Banking [Member] | Talmer Bank & Trust [Member]
Business Acquisition [Line Items]
Date of acquisition																	Aug. 08, 2014
Number of Locations																	11
Fair value of assets acquired, at the acquisition date																	361,300,000
Fair value of loans acquired, at the acquisition date																	41,500,000
Fair value of liabilities assumed, at the acquisition date																	361,300,000
Fair value of deposits																	354,900,000
Additional goodwill recorded on acquisition																	9,700,000
Wealth Management [Member]
Business Acquisition [Line Items]
Additional goodwill recorded on acquisition	250,000
Wealth Management [Member] | Talmer Bank & Trust [Member]
Business Acquisition [Line Items]
Date of acquisition																	Aug. 08, 2014
Additional goodwill recorded on acquisition																	$ 250,000