Business Combinations (Narrative) (Detail)						6 Months Ended	66 Months Ended
	Jan. 16, 2015 USD ($) locations	Aug. 08, 2014 USD ($) locations	Jul. 11, 2014 USD ($)	May. 16, 2014 USD ($)	Apr. 28, 2014 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2015 financial_institution
Business Acquisition [Line Items]
Additional goodwill recorded on acquisition						$ 17,383,000
FDIC loss sharing percentage on purchased loans, OREO, and certain other assets						80.00%
Delavan Bancshares
Business Acquisition [Line Items]
Effective date of acquisition	Jan. 16, 2015
Number of locations | locations	4
Assets acquired	$ 224,100,000
Loans acquired	128,000,000
Liabilities assumed	186,400,000
Assumed deposits	170,200,000
Additional goodwill recorded on acquisition	$ 17,400,000
Talmer Bank & Trust
Business Acquisition [Line Items]
Effective date of acquisition		Aug. 08, 2014
Number of locations | locations		11
Assets acquired		$ 361,300,000
Loans acquired		41,500,000
Liabilities assumed		361,300,000
Assumed deposits		354,900,000
Additional goodwill recorded on acquisition		$ 9,700,000
THE National Bank
Business Acquisition [Line Items]
Effective date of acquisition			Jul. 11, 2014
Assets acquired			$ 94,100,000
Loans acquired			75,000,000
Assumed deposits			36,200,000
Additional goodwill recorded on acquisition			$ 16,300,000
Urban Partnership Bank, Stone Park branch
Business Acquisition [Line Items]
Effective date of acquisition				May 16, 2014
Liabilities assumed				$ 5,500,000
Assumed deposits				5,400,000
Additional goodwill recorded on acquisition				$ 678,000
FDIC Assisted
Business Acquisition [Line Items]
Number of FDIC assisted banks acquired | financial_institution							9
Policy Billing Services Inc. And Equity Premium Finance Inc.
Business Acquisition [Line Items]
Effective date of acquisition					Apr. 28, 2014
Loans acquired					$ 7,400,000
Additional goodwill recorded on acquisition					$ 6,500,000
Number of affiliated companies acquired					2