Business Combinations (FDCI Assisted Transactions) (Details) (USD $)	3 Months Ended		12 Months Ended	24 Months Ended	0 Months Ended	12 Months Ended			12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011	Mar. 31, 2012	Feb. 10, 2012 Charter National [Member]	Dec. 31, 2010 Lincoln Park [Member]	Dec. 31, 2010 Wheatland [Member]	Dec. 31, 2010 Lincoln Park And Wheatland [Member]	Dec. 31, 2010 Ravenswood [Member]	Dec. 31, 2011 First Chicago [Member]	Dec. 31, 2011 Community First Bank - Chicago [Member]	Dec. 31, 2011 The Bank Of Commerce [Member]	Dec. 31, 2010 FDIC- Assisted Transaction [Member]
Business Acquisition [Line Items]
Number of FDIC assisted banks acquired				7
FDIC loss sharing percentage on purchased loans, OREO, and certain other assets	80.00%
Transactions resulting in bargain purchase of gains	$ 263,212,000	$ 124,785,000	$ 344,251,000	$ 263,212,000	$ 13,200,000			$ 113,800,000	$ 44,000,000	$ 273,300,000	$ 6,700,000	$ 48,900,000
Bargain purchase gains recognized	$ 840,000	$ 9,838,000	$ 38,000,000		$ 840,000	$ 4,200,000	$ 22,300,000		$ 6,800,000	$ 27,400,000	$ 2,000,000	$ 8,600,000	$ 33,300,000