Acquisitions - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended		6 Months Ended
	May 09, 2019	Oct. 12, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jan. 16, 2019
Business Acquisition [Line Items]
Acquisition and integration related expenses			$ 9,514	$ 0	$ 13,205	$ 0
Bridgeview Bancorp, Inc.
Business Acquisition [Line Items]
Total assets	$ 1,161,640
Total deposits	986,754
Loans	$ 709,889
Fixed exchange ratio (in shares)	0.2767
Cash paid per share (in dollars per share)	$ 1.66
Consideration transferred	$ 135,352
Common stock, shares issued (in shares)	4,728,541
Cash paid	$ 37,140
Goodwill	$ 57,377
Northern Oak Wealth Management, Inc.
Business Acquisition [Line Items]
Assets under management acquired							$ 800,000
Northern States Financial Corporation
Business Acquisition [Line Items]
Total assets		$ 578,672
Total deposits		463,160
Loans		$ 284,924
Fixed exchange ratio (in shares)		0.0363
Consideration transferred		$ 83,303
Common stock, shares issued (in shares)		3,310,912
Cash paid		$ 0
Goodwill		$ 30,123