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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, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019 | Dec. 31, 2019
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans | $ 4,562 | $ 25,800 | $ 11,586 | $ 36,712 |
Commercial real estate | Commercial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans | 171 | 23,784 | 2,381 | 29,747 |
Commercial and industrial | Commercial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans | 4,022 | 1,527 | 5,381 | 5,860 |
Commercial construction | Commercial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans | 0 |  | 2,561 |  |
Residential Mortgage | Consumer |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans | 96 | 0 | 743 | 160 |
Home equity | Consumer |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans | 269 | 485 | 515 | 935 |
Installment and other consumer | Consumer |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans | $ 4 | $ 4 | 4 | $ 10 |
Performing TDRs |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 18,478 |  | $ 36,960
Performing TDRs | Commercial real estate | Commercial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 19 |  | 22,233
Performing TDRs | Commercial and industrial | Commercial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 7,322 |  | 6,909
Performing TDRs | Commercial construction | Commercial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 3,986 |  | 1,425
Performing TDRs | Business banking | Commercial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 1,539 |  |
Performing TDRs | Consumer real estate | Consumer |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 5,606 |  |
Performing TDRs | Residential Mortgage | Consumer |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  |  |  | 2,013
Performing TDRs | Home equity | Consumer |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  |  |  | 4,371
Performing TDRs | Other consumer | Consumer |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 6 |  |
Performing TDRs | Installment and other consumer | Consumer |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  |  |  | 9
Nonperforming TDRs |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 18,648 |  | 8,912
Nonperforming TDRs | Commercial real estate | Commercial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 14,504 |  | 6,713
Nonperforming TDRs | Commercial and industrial | Commercial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 1,549 |  | 695
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 |  |  | 441 |  |
Nonperforming TDRs | Consumer real estate | Consumer |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 2,154 |  |
Nonperforming TDRs | Residential Mortgage | Consumer |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  |  |  | 822
Nonperforming TDRs | Home equity | Consumer |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  |  |  | 678
Nonperforming TDRs | Other consumer | Consumer |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 0 |  |
Nonperforming TDRs | Installment and other consumer | Consumer |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  |  |  | 4
Total TDRs |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 37,126 |  | 45,872
Total TDRs | Commercial real estate | Commercial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 14,523 |  | 28,946
Total TDRs | Commercial and industrial | Commercial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 8,871 |  | 7,604
Total TDRs | Commercial construction | Commercial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 3,986 |  | 1,425
Total TDRs | Business banking | Commercial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 1,980 |  |
Total TDRs | Consumer real estate | Consumer |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | 7,760 |  |
Total TDRs | Residential Mortgage | Consumer |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  |  |  | 2,835
Total TDRs | Home equity | Consumer |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  |  |  | 5,049
Total TDRs | Other consumer | Consumer |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  | $ 6 |  |
Total TDRs | Installment and other consumer | Consumer |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  |  |  | $ 13

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