Shareholders' Equity And Earnings Per Share (Narrative) (Detail) (USD $)	0 Months Ended	1 Months Ended			3 Months Ended		12 Months Ended				1 Months Ended					1 Months Ended	3 Months Ended			0 Months Ended	12 Months Ended		3 Months Ended	12 Months Ended				0 Months Ended	12 Months Ended		0 Months Ended
	Dec. 19, 2008	Jan. 31, 2014	Feb. 28, 2013	Mar. 31, 2012	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2010	Dec. 31, 2013	Jul. 19, 2013	Dec. 07, 2010	Jul. 19, 2013 Series A Preferred Stock [Member]	Aug. 31, 2008 Series A Preferred Stock [Member]	Mar. 31, 2014 Series A Preferred Stock [Member]	Dec. 31, 2013 Series A Preferred Stock [Member]	Mar. 31, 2013 Series A Preferred Stock [Member]	Mar. 31, 2012 Series C Preferred Stock [Member]	Dec. 31, 2013 Series C Preferred Stock [Member]	Mar. 31, 2014 Series C Preferred Stock [Member]	Mar. 31, 2013 Series C Preferred Stock [Member]	Dec. 15, 2013 Equity Component	Dec. 31, 2013 Equity Component	Dec. 31, 2010 Equity Component	Mar. 31, 2014 Junior Subordinated Debt [Member]	Dec. 31, 2013 Junior Subordinated Debt [Member]	Dec. 31, 2010 Junior Subordinated Debt [Member]	Dec. 15, 2013 Junior Subordinated Debt [Member]	Dec. 07, 2010 Junior Subordinated Debt [Member]	Mar. 15, 2011 Junior Subordinated Debt [Member] Debt [Member]	Dec. 31, 2010 Junior Subordinated Debt [Member] Debt [Member]	Dec. 07, 2010 Junior Subordinated Debt [Member] Debt [Member]	May 01, 2013 First Lansing Bancorp, Inc. [Member]
Temporary Equity [Line Items]
Amount Of Tangible Equity Units Sold										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		Dec. 15, 2013				Dec. 15, 2013
Debt Instrument, Frequency of Periodic Payment																								quarterly	quarterly				quarterly
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%				9.50%
Quarterly installments on amortizing note																												0.989583	0.9375
Settlement rate, shares																				1.3333
Number Of Consecutive Trading Days																					20
Amount Per Share Reclassified From Surplus To Common Stock																				$ 1.00
Preferred stock, shares issued												50,000	0	0	50,000	126,500	126,477	126,477	126,500
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	$ 0	$ 49,941,000	$ 126,500,000	$ 126,477,000	$ 126,477,000	$ 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
Preferred Stock, Shares Converted											50,000						23
Stock Issued During Period, Shares, Conversion of Convertible Securities											1,944,000						558
Common stock, no par value									$ 0
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
Warrants Holders Common Stock Purchase Price Per Share					$ 30.50
Warrants outstanding				19,000	0
Warrants Exercised			1,000	18,000
Common stock, shares issued																															648,286
Cash dividends declared per common share		$ 0.10			$ 0.10	$ 0.09
Common Stock Dividends Per Share Declared Annualized		$ 0.40
Dividends Payable, Date to be Paid		Feb. 20, 2014
Dividends Payable, Date of Record		Feb. 06, 2014