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Loans and Loans Held for Sale - Summary of Restructured Loans (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020 | Dec. 31, 2020
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans | $ 689 | $ 4,561 | $ 8,513 | $ 11,585 |
Commercial real estate | Commercial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans | 0 | 0 | 0 | 2,210 |
Commercial and industrial | Commercial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans | 341 | 4,022 | 5,968 | 5,284 |
Commercial construction | Commercial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans | 0 | 0 | 0 | 2,561 |
Business banking | Commercial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans | 0 | 171 | 1,500 | 268 |
Consumer real estate | Consumer |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans | 348 | 364 | 1,045 | 1,258 |
Other consumer | Consumer |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans | $ 0 | $ 4 | 0 | $ 4 |
Total TDRs |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 27,815 |  | $ 46,748
Total TDRs | Commercial real estate | Commercial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 15,345 |  | 16,668
Total TDRs | Commercial and industrial | Commercial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 1,762 |  | 16,975
Total TDRs | Commercial construction | Commercial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 0 |  | 3,267
Total TDRs | Business banking | Commercial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 3,139 |  | 1,933
Total TDRs | Consumer real estate | Consumer |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 7,569 |  | 7,900
Total TDRs | Other consumer | Consumer |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 0 |  | 5
Performing TDRs |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 13,782 |  | 17,460
Performing TDRs | Commercial real estate | Commercial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 4,252 |  | 14
Performing TDRs | Commercial and industrial | Commercial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 1,762 |  | 7,090
Performing TDRs | Commercial construction | Commercial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 0 |  | 3,267
Performing TDRs | Business banking | Commercial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 1,647 |  | 1,503
Performing TDRs | Consumer real estate | Consumer |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 6,120 |  | 5,581
Performing TDRs | Other consumer | Consumer |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 0 |  | 5
Nonperforming TDRs |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 14,033 |  | 29,289
Nonperforming TDRs | Commercial real estate | Commercial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 11,093 |  | 16,654
Nonperforming TDRs | Commercial and industrial | Commercial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 0 |  | 9,885
Nonperforming TDRs | Commercial construction | Commercial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 0 |  | 0
Nonperforming TDRs | Business banking | Commercial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 1,492 |  | 430
Nonperforming TDRs | Consumer real estate | Consumer |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 1,448 |  | 2,319
Nonperforming TDRs | Other consumer | Consumer |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | $ 0 |  | $ 0

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