Acquisition - Summary of Fair Values of Assets and Liabilities Assumed as of Acquisition Date (Details) - USD ($) $ in Thousands	May 15, 2019	Apr. 30, 2019	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Consideration paid
Goodwill			$ 148,353	$ 148,353	$ 148,353	$ 145,638	$ 145,638	$ 128,177
Oak Park River Forest Bankshares, Inc.
Assets
Cash and cash equivalents		$ 10,469
Securities available-for-sale		30,343
Restricted stock		414
Loans		257,423
Premises and equipment		3,488
Other real estate owned		2,201
Other intangible assets		6,220
Bank-owned life insurance		3,485
Deferred tax assets, net		5,925
Other assets		1,231
Total assets acquired		321,199
Liabilities
Deposits		290,171
Line of credit		5,655
Federal Home Loan Bank advances		5,300
Accrued expenses and other liabilities		4,766
Total liabilities assumed		305,892
Net assets acquired		15,307
Consideration paid
Common stock (1,464,558 shares issued at $20.02 per share)		29,320
Consideration paid in cash	$ 4,200	6,163
Total consideration paid		35,483
Goodwill		$ 20,176