Shareholders' Equity And Earnings Per Share (Narrative) (Detail) (USD $)	0 Months Ended	1 Months Ended	9 Months Ended		12 Months Ended		0 Months Ended	2 Months Ended	1 Months Ended					1 Months Ended				9 Months Ended		9 Months Ended		9 Months Ended
	Dec. 19, 2008	Mar. 31, 2012	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2010	Dec. 07, 2010	Jul. 31, 2011 Great Lakes Advisors, Inc [Member]	Sep. 30, 2012 Great Lakes Advisors, Inc [Member]	Sep. 30, 2011 Elgin State Bancorp, Inc [Member]	Aug. 31, 2008 Series A Preferred Stock [Member]	Sep. 30, 2012 Series A Preferred Stock [Member]	Dec. 31, 2011 Series A Preferred Stock [Member]	Sep. 30, 2011 Series A Preferred Stock [Member]	Mar. 31, 2012 Series C Preferred Stock [Member]	Sep. 30, 2012 Series C Preferred Stock [Member]	Dec. 31, 2011 Series C Preferred Stock [Member]	Sep. 30, 2011 Series C Preferred Stock [Member]	Sep. 30, 2012 Maximum [Member]	Sep. 30, 2012 Maximum [Member] Market Value Of Common Stock Greater Than Thirty Dollars But Less Than Thirty Seven Point Five Zero Dollars [Member]	Sep. 30, 2012 Minimum [Member]	Sep. 30, 2012 Minimum [Member] Market Value Of Common Stock Greater Than Thirty Dollars But Less Than Thirty Seven Point Five Zero Dollars [Member]	Sep. 30, 2012 Equity [Member]
Temporary Equity [Line Items]
Tangible equity unit, proceeds						4,600,000
Rate on tangible equity units						7.50%
Tangible equity unit public offering price per unit						50
Net proceeds on sale of tangible equity units					$ 222,700,000
Junior subordinated amortizing note, scheduled final installment payment date					Dec. 15, 2013
Debt component maturity date			Dec. 15, 2013		Dec. 15, 2013
Percentage of fair value of debt component quarterly cash payments			7.50%
Discount rate on debt component			9.50%
Risk-free rate			0.70%	1.20%																		0.95%
Expected stock price volatility minimum																						35.00%
Expected stock price volatility maximum																						45.00%
Percent of dividend yield plus stock borrow cost																						0.85%
Equity term, years			4 years 6 months	6 years 1 month 6 days																		3 years 7 days
Junior subordinated amortizing note, initial principal amount			9.728182
Junior subordinated amortizing note, bearing interest			9.50%
Quarterly installments on amortizing note			0.9375
Extended installment period on amortizing note			Dec. 15, 2015
Settlement rate, shares																		1.6666		1.3333
Applicable Market Value Of Company Common Stock Per Share																			$ 37.5		$ 30.00
Amount Reclassifed from Additional Paid in Capital to Common Stock Per Share			$ 1.00
Number Of Consecutive Trading Days			20 days
Non-cumulative perpetual convertible preferred stock, issued										50,000				126,500
Preferred stock, liquidation value per share										$ 1,000	$ 1,000	$ 1,000	$ 1,000	$ 1,000	$ 1,000	$ 0	$ 0
Liquidation of preference shares, equity offering										$ 50,000,000				$ 126,500,000
Preferred stock, dividend rate, percentage										8.00%				5.00%
Convertible preferred stock conversion rate of common stock to Series A preferred stock										38.88				24.3132
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	1,643,295		1,643,295
Investment Warrants, Exercise Price	$ 22.82
Warrant Termination Period	10 years
Common Stock, shares issued in acquisition							529,087	25,493	353,650
Warrants holders common stock purchase price per share			$ 30.50
Warrants exercised		18,000
Warrants outstanding			1,000	19,000
Warrants expiration date			Feb. 01, 2013