Business Combinations (All Other Acquisitions) (Detail) (USD $)	9 Months Ended	21 Months Ended	24 Months Ended	0 Months Ended
	Sep. 30, 2013	Sep. 30, 2013 financial_institution	Dec. 31, 2011 financial_institution	Jul. 20, 2012 Second Federal [Member]	May 01, 2013 First Lansing Bancorp, Inc. [Member]	Dec. 12, 2012 HPK Financial Corporation [Member] locations	Apr. 13, 2012 Suburban Bank & Trust Company [Member]	Mar. 30, 2012 Suburban Bank & Trust Company [Member]	Jun. 08, 2012 Macquarie Premium Funding Inc [Member]	May 01, 2013 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]
Number of FDIC assisted banks acquired		3	6
FDIC loss sharing percentage on purchased loans, OREO, and certain other assets	80.00%
Divestiture of businesses, deposits disposed												$ 149,000,000
Effective date of acquisition				Jul. 20, 2012	May 01, 2013	Dec. 12, 2012	Apr. 13, 2012	Mar. 30, 2012	Jun. 08, 2012
Number of locations						2				7	1
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets				171,625,000	373,400,000	371,600,000
Business acquisition, loans acquired				0	123,000,000	118,500,000	3,000,000		213,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities				171,582,000	334,700,000	344,100,000
Assumed deposits					331,400,000	243,800,000	52,000,000
Additional goodwill recorded on acquisition	13,960,000				14,000,000	12,600,000	1,500,000	1,800,000	21,900,000
Assets under administration								$ 160,000,000