Business Combinations (Narrative) (Details) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended		9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended		9 Months Ended	12 Months Ended	9 Months Ended			0 Months Ended	12 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010	Oct. 22, 2010	Sep. 30, 2011 Lincoln Park [Member]	Dec. 31, 2010 Lincoln Park [Member]	Sep. 30, 2011 Wheatland [Member]	Dec. 31, 2010 Wheatland [Member]	Dec. 31, 2010 Lincoln Park And Wheatland [Member]	Sep. 30, 2011 Ravenswood [Member]	Dec. 31, 2010 Ravenswood [Member]	Sep. 30, 2011 First Chicago [Member]	Sep. 30, 2011 Community First Bank - Chicago [Member]	Sep. 30, 2011 The Bank Of Commerce [Member]	Oct. 22, 2010 Other Bank Acquisitions [Member]	Dec. 31, 2010 River City Mortgage, LLC [Member]	Dec. 31, 2010 Woodfield Planning Corporation [Member]	Sep. 30, 2011 Elgin State Bancorp, Inc [Member]	Jul. 31, 2011 Great Lakes Advisors, Inc [Member]
FDIC loss sharing percentage on purchased loans, OREO, and certain other assets			80.00%
Fair value of the reimbursable losses											$ 113,800,000
Transactions resulting in bargain purchase of gains	379,306,000	161,640,000	379,306,000	161,640,000	118,182,000								44,000,000	273,300,000	6,700,000	48,900,000
Bargain purchase gains	27,390,000	6,593,000	37,974,000	43,981,000	33,300,000			4,200,000		22,300,000			6,800,000	27,400,000	2,000,000	8,600,000
Fair value of assets acquired, at the acquisition date							157,078,000		343,870,000			173,919,000		768,873,000	50,891,000	173,986,000	22,900,000
Fair value of loans acquired, at the acquisition date							103,420,000		175,277,000			97,956,000		330,203,000	27,332,000	77,887,000	10,700,000
Fair value of liabilities assumed, at the acquisition date							192,018,000		415,560,000			122,943,000		741,508,000	49,779,000	168,472,000
Mortgage loans acquired																		500,000,000	180,000,000
Goodwill, Acquired During Period			21,179,000														1,700,000
Approximate fair value of assumed liabilities						22,900,000
Approximate fair value of assumed liabilities, deposits						22,800,000
Business acquisition, assets acquired																				263,200,000	24,800,000
Business acquisition, liabilities assumed																				248,400,000	7,600,000
Business acquisition, loans acquired																				145,700,000
Business acquisition, deposits acquired																				241,100,000
Business acquisition, goodwill amount																				3,800,000	15,200,000
Assets under management acquired																					$ 2,400,000,000