Subsequent Events Subsequent Events (Narrative) (Detail) (Subsequent Event [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
Jun. 30, 2015 locations
Suburban Illinois Bancorp [Member]
Subsequent Event [Line Items]
Business Acquisition, Date of Acquisition Agreement	Apr. 02, 2015
Number of locations	10
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	$ 470.0
Business Combination, Acquired Receivables, Fair Value	297.0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deposits	411.0
North Bank [Member]
Subsequent Event [Line Items]
Business Acquisition, Date of Acquisition Agreement	Mar. 30, 2015
Number of locations	2
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	108.0
Business Combination, Acquired Receivables, Fair Value	55.0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deposits	96.0
Community Financial Shares Inc. [Member]
Subsequent Event [Line Items]
Business Acquisition, Date of Acquisition Agreement	Mar. 02, 2015
Number of locations	4
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	343.0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deposits	$ 310.0

Date when the business acquisition agreement was executed, in CCYY-MM-DD format.

No definition available.

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- Definition

For receivables acquired in a business combination, excluding certain loans and debt securities acquired in a transfer (as defined), this element represents the fair value of the receivables acquired, by major class of receivable, such as loans, direct finance leases (as defined), and any other class of receivables.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)(1)

-URI http://asc.fasb.org/extlink&oid=56956791&loc=d3e4845-128472

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of assets acquired at the acquisition date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=56956791&loc=d3e4845-128472

+ Details

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- Details

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- Definition

Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deposits

+ References

No definition available.

+ Details

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- Definition

Number of Locations

+ References

No definition available.

+ Details

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Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Details

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- Details

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- Details

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