Acquisitions - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands				3 Months Ended		9 Months Ended
	Aug. 27, 2019	May 09, 2019	Oct. 12, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Jun. 30, 2019	Jan. 16, 2019
Business Acquisition [Line Items]
Acquisition and integration related expenses				$ 3,397	$ 60	$ 16,602	$ 60
Bankmanagers Corporation
Business Acquisition [Line Items]
Announced assets to be acquired								$ 1,000,000
Announced deposits to be acquired								815,000
Announced loans to be acquired								$ 700,000
Fixed exchange ratio (in shares)	29.9675
Cash paid per share (in dollars per share)	$ 623.02
Consideration to be transferred	$ 195,000
Bridgeview Bancorp, Inc.
Business Acquisition [Line Items]
Fixed exchange ratio (in shares)		0.2767
Cash paid per share (in dollars per share)		$ 1.66
Total assets		$ 1,161,791
Total deposits		986,754
Loans		711,688
Consideration transferred		$ 135,352
Common stock, shares issued (in shares)		4,728,541
Cash paid		$ 37,140
Goodwill		$ 57,651
Northern Oak Wealth Management, Inc.
Business Acquisition [Line Items]
Assets under management acquired									$ 800,000
Northern States Financial Corporation
Business Acquisition [Line Items]
Fixed exchange ratio (in shares)			0.0363
Total assets			$ 579,333
Total deposits			463,160
Loans			284,940
Consideration transferred			$ 83,303
Common stock, shares issued (in shares)			3,310,912
Cash paid			$ 0
Goodwill			$ 30,016