Business Combinations - Schedule of Changes to Goodwill (Detail) $ in Thousands	3 Months Ended
Mar. 31, 2016 USD ($)
Business Acquisition [Line Items]
Goodwill, Beginning balance	$ 85,212
Goodwill, Ending balance	84,854
Alliance Bancorp, Inc. [Member]
Business Acquisition [Line Items]
Goodwill, Beginning balance	36,425
Goodwill, Ending balance	36,067
Alliance Bancorp, Inc. [Member] \| Deferred Income Taxes [Member]
Business Acquisition [Line Items]
Effect of adjustments	(186)
Alliance Bancorp, Inc. [Member] \| Other Assets [Member]
Business Acquisition [Line Items]
Effect of adjustments	(597)
Alliance Bancorp, Inc. [Member] \| Other Liabilities [Member]
Business Acquisition [Line Items]
Effect of adjustments	$ 425

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

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Amount of increase (decrease) from adjustments after acquisition date under purchase accounting of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 25
-Paragraph 16
-URI http://asc.fasb.org/extlink&oid=34752592&loc=d3e961-128460

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

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