Business Combinations (Narrative) (Detail) (USD $)	3 Months Ended	51 Months Ended	0 Months Ended			12 Months Ended
	Mar. 31, 2014	Mar. 31, 2014 financial_institution	Oct. 18, 2013 Diamond Bancorp, Inc [Member] locations	May 01, 2013 First Lansing Bancorp, Inc. [Member]	Oct. 02, 2013 Surety Financial Services [Member]	Sep. 30, 2013 Surety Financial Services [Member] locations	May 01, 2013 Southwest Suburbs of Chicago, Illinois [Member] First Lansing Bancorp, Inc. [Member] locations	May 01, 2013 Northwest Indiana [Member] First Lansing Bancorp, Inc. [Member] locations	Feb. 01, 2013 Second Federal [Member]
Business Acquisition [Line Items]
Effective date of acquisition			Oct. 18, 2013	May 01, 2013	Oct. 01, 2013
Number of locations			4			5	7	1
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets			$ 172,500,000	$ 373,400,000
Business acquisition, loans acquired			91,700,000	123,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities			169,100,000	334,700,000
Assumed deposits			140,200,000	331,400,000
Additional goodwill recorded on acquisition	0		8,400,000	14,000,000	9,500,000
Number of FDIC assisted banks acquired		9
FDIC loss sharing percentage on purchased loans, OREO, and certain other assets	80.00%
Divestiture of businesses, deposits disposed									149,000,000
Mortgage Loan Originations						$ 1,000,000,000