Shareholders' Equity And Earnings Per Share (Narrative) (Detail) (USD $)	0 Months Ended	1 Months Ended		9 Months Ended		12 Months Ended				1 Months Ended					1 Months Ended				9 Months Ended				9 Months Ended		12 Months Ended	9 Months Ended	12 Months Ended		0 Months Ended	1 Months Ended
	Dec. 19, 2008	Feb. 28, 2013	Mar. 31, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2010	Jul. 19, 2013	Dec. 31, 2012	Dec. 07, 2010	Jul. 19, 2013 Series A Preferred Stock [Member]	Aug. 31, 2008 Series A Preferred Stock [Member]	Sep. 30, 2013 Series A Preferred Stock [Member]	Dec. 31, 2012 Series A Preferred Stock [Member]	Sep. 30, 2012 Series A Preferred Stock [Member]	Mar. 31, 2012 Series C Preferred Stock [Member]	Sep. 30, 2013 Series C Preferred Stock [Member]	Dec. 31, 2012 Series C Preferred Stock [Member]	Sep. 30, 2012 Series C Preferred Stock [Member]	Sep. 30, 2013 Applicable market value of Company common stock - Greater than thirty dollars but less than thirty seven point five zero dollars	Sep. 30, 2013 Applicable market value of Company common stock - Greater than thirty dollars but less than thirty seven point five zero dollars	Sep. 30, 2013 Maximum [Member]	Sep. 30, 2013 Maximum [Member] Applicable market value of Company common stock - Greater than thirty dollars but less than thirty seven point five zero dollars	Sep. 30, 2013 Minimum [Member]	Sep. 30, 2013 Minimum [Member] Applicable market value of Company common stock - Greater than thirty dollars but less than thirty seven point five zero dollars	Dec. 31, 2010 Equity Component	Sep. 30, 2013 Junior Subordinated Debt [Member]	Dec. 31, 2010 Junior Subordinated Debt [Member]	Dec. 07, 2010 Junior Subordinated Debt [Member]	May 01, 2013 First Lansing Bancorp, Inc. [Member]	Dec. 31, 2012 HPK Financial Corporation [Member]	Aug. 31, 2012 Great Lakes Advisors, Inc [Member]	Jul. 31, 2011 Great Lakes Advisors, Inc [Member]
Temporary Equity [Line Items]
Debt Instrument, Frequency of Periodic Payment																										quarterly	quarterly
Tangible equity unit, proceeds									4,600,000
Rate on tangible equity units									7.50%
Tangible equity unit public offering price per unit									$ 50.00
Net proceeds on sale of tangible equity units						$ 222,700,000
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%	0.70%																				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	4 years 6 months																				3 years 7 days
Junior subordinated amortizing note, initial principal amount																												9.728182
Contractual rate																										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																						$ 37.5		$ 30.00
Amount Reclassifed from Additional Paid in Capital to Common Stock Per Share				$ 1.00
Number Of Consecutive Trading Days				20
Preferred stock, liquidation value per share											$ 1,000	$ 1,000	$ 1,000	$ 1,000	$ 1,000	$ 1,000	$ 1,000	$ 1,000
Preferred stock, value											50,000,000	0	49,906,000	49,871,000		126,500,000	126,500,000	126,500,000
Liquidation of preference shares, equity offering															$ 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
Preferred stock, shares issued										50,000	50,000	0	50,000	50,000	126,500	126,500	126,500	126,500
Stock Issued During Period, Shares, Conversion of Convertible Securities										1,944,000
Common stock, no par value
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																													648,286	372,530	25,493	529,087
Warrants holders common stock purchase price per share				$ 30.50
Warrants exercised		1,000	18,000
Warrants outstanding			19,000	0
Warrants expiration date				Feb. 01, 2013
Settlement Rate, Market Value																			50.00	50.00