Acquisition - Additional Information (Details) - USD ($)			3 Months Ended	9 Months Ended		12 Months Ended
	May 15, 2019	Apr. 30, 2019	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Goodwill			$ 145,638,000	$ 148,353,000	$ 145,638,000	$ 148,353,000	$ 148,353,000	$ 145,638,000	$ 128,177,000
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		585,000
Goodwill		$ 20,176,000
Oak Park River Forest Bankshares, Inc. | Non-interest Expense
Business Acquisition [Line Items]
Acquisition advisory expenses					2,300,000	2,300,000
Core system conversion expenses			1,200,000		$ 1,900,000	$ 2,000,000.0
Merger related income from legal fee credit			$ 135,000