Business Combinations - Schedule of Changes to Goodwill (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2016 USD ($)
Business Acquisition [Line Items]
Goodwill, Beginning balance	$ 85,212
Goodwill, Ending balance	84,852
Alliance Bancorp, Inc. [Member]
Business Acquisition [Line Items]
Goodwill, Beginning balance	36,425
Goodwill, Ending balance	36,065
Alliance Bancorp, Inc. [Member] | Deferred Income Taxes [Member]
Business Acquisition [Line Items]
Effect of adjustments	(125)
Alliance Bancorp, Inc. [Member] | Other Assets [Member]
Business Acquisition [Line Items]
Effect of adjustments	(655)
Alliance Bancorp, Inc. [Member] | Other Liabilities [Member]
Business Acquisition [Line Items]
Effect of adjustments	$ 420