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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
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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 |  |  |  |

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- Definition Fair value at acquisition of acquired loans accounted for as debt securities with evidence of deterioration of credit quality. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=118939070&loc=d3e15032-111544 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 30 -Section 15 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=118938799&loc=d3e13503-111538 + Details
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- Definition Amount of deposits held by the entity that have been reclassified as loan balances receivable, for example, but not limited to, overdrafts receivable. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 405 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=116652737&loc=d3e64164-112818 + Details
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- Definition Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.7(d)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953423-111524 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (b)(1)(ii) -URI http://asc.fasb.org/extlink&oid=118939070&loc=d3e15032-111544 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953423-111524 Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SAB Topic 6.L.1) -URI http://asc.fasb.org/extlink&oid=27010918&loc=d3e74567-122707 + Details
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