Loan and Lease Receivables - Additional Information (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019	Apr. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Accounts Notes And Loans Receivable [Line Items]
Total loans and leases	$ 3,854,918,000	$ 3,780,636,000
Loans held for sale pledged as security for borrowings	1,900,000,000	1,800,000,000
Allowance for loan and lease losses	41,840,000	31,936,000		$ 27,106,000	$ 25,201,000
Acquired Impaired Loans
Accounts Notes And Loans Receivable [Line Items]
Loans acquired			$ 52,927,000
Allowance for loan and lease losses	4,300,000	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	5,640,000	6,484,000
Overdraft deposits reclassified as loans	447,000	852,000
Allowance for loan and lease losses	53,000	50,000		$ 63,000	$ 49,000
U.S. Government Guaranteed Loans
Accounts Notes And Loans Receivable [Line Items]
Total loans and leases	$ 122,200,000	$ 119,800,000