Loan and Lease Receivables - Additional Information (Details) - USD ($)	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Apr. 30, 2019	Dec. 31, 2018
Accounts Notes And Loans Receivable [Line Items]
Total loans and leases	$ 4,379,130,000		$ 3,780,636,000
Loans held for sale pledged as security for borrowings	2,400,000,000		1,800,000,000
Allowance for loan and lease losses	61,258,000	$ 51,300,000	31,936,000	$ 31,585,000	$ 31,132,000		$ 25,201,000
Acquired Impaired Loans
Accounts Notes And Loans Receivable [Line Items]
Loans acquired						$ 52,927,000
Allowance for loan and lease losses	5,000,000.0		2,800,000
Acquired Impaired Loans | Oak Park River Forest Bankshares, Inc.
Accounts Notes And Loans Receivable [Line Items]
Loans acquired						$ 52,900,000
Acquired Non-Impaired Loans and Leases | Oak Park River Forest Bankshares, Inc.
Accounts Notes And Loans Receivable [Line Items]
Loans acquired			204,500,000
Installment and Other
Accounts Notes And Loans Receivable [Line Items]
Total loans and leases	3,072,000		6,484,000
Overdraft deposits reclassified as loans	301,000		852,000
Allowance for loan and lease losses	37,000	$ 36,000	50,000	$ 55,000	$ 67,000		$ 49,000
U.S. Government Guaranteed Loans
Accounts Notes And Loans Receivable [Line Items]
Total loans and leases	765,700,000		119,800,000
Discount on the unguaranteed portion of government guaranteed loans	$ 25,700,000		$ 23,100,000