Acquisitions - Additional Information (Details) - USD ($)				3 Months Ended		9 Months Ended
	May 15, 2019	Apr. 30, 2019	May 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Goodwill				$ 145,638,000	$ 127,536,000	$ 145,638,000	$ 127,536,000	$ 145,638,000	$ 128,177,000	$ 127,536,000	$ 54,562,000
Oak Park River Forest Bankshares, Inc.
Business Acquisition [Line Items]
Business acquisition date of agreement						Apr. 30, 2019
Right to receive common stock upon conversion		7.9321
Consideration paid in cash	$ 4,200,000	$ 6,163,000
Common stock outstanding value per share		$ 33.375
Common stock issued price per share		$ 20.02
Issuance of common shares		1,464,558
Value of common stock consideration		$ 29,300,000
Options to acquire common stock shares		35,870
Option to acquire common stock value		$ 4,200,000
Total merger consideration		35,483,000
Stock issuance costs		429,000
Goodwill		$ 17,461,000
Oak Park River Forest Bankshares, Inc. | Non-interest Expense
Business Acquisition [Line Items]
Acquisition advisory expenses						$ 2,300,000
Merger related income from legal fee credit				135,000
Core system conversion expenses				1,200,000		$ 1,900,000
First Evanston Bancorp, Inc.
Business Acquisition [Line Items]
Business acquisition date of agreement						May 31, 2018
Right to receive common stock upon conversion			3.994
Consideration paid in cash			$ 27,004,000
Common stock outstanding value per share			$ 16.136
Common stock issued price per share			$ 21.62
Issuance of common shares			6,682,850
Value of common stock consideration			$ 144,500,000
Options to acquire common stock shares			144,090
Option to acquire common stock value			$ 7,600,000
Total merger consideration			179,131,000
Stock issuance costs			852,000
Goodwill			$ 73,615,000
Options to acquire conversion of common stock shares			680,787
First Evanston Bancorp, Inc. | Non-interest Expense
Business Acquisition [Line Items]
Acquisition advisory expenses				0	50,000	$ 0	1,700,000
Core system conversion expenses				$ 76,000	$ 213,000	$ 2,000,000	$ 9,200,000