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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, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017 | Dec. 31, 2017
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |
Restructured loans | [1] | $ 633 | $ 1,471 | $ 11,699 | $ 4,522 |
Commercial real estate |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |
Restructured loans | [1] | 250 | 400 | 250 | 500 |
Commercial and industrial |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |
Restructured loans | [1] | 0 | 816 | 10,348 | 3,044 |
Residential mortgage |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |
Restructured loans | [1] | 186 | 0 | 380 | 32 |
Home equity |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |
Restructured loans | [1] | 191 | 70 | 715 | 726 |
Installment and other consumer |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |
Restructured loans | [1] | $ 6 | $ 185 | 6 | $ 220 |
Performing TDRs |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |
Restructured loans |  |  |  | 22,226 |  | $ 14,901
Performing TDRs | Commercial real estate |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |
Restructured loans |  |  |  | 2,095 |  | 2,579
Performing TDRs | Commercial and industrial |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |
Restructured loans |  |  |  | 11,874 |  | 3,946
Performing TDRs | Commercial construction |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |
Restructured loans |  |  |  | 2,400 |  | 2,420
Performing TDRs | Residential mortgage |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |
Restructured loans |  |  |  | 2,229 |  | 2,039
Performing TDRs | Home equity |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |
Restructured loans |  |  |  | 3,612 |  | 3,885
Performing TDRs | Installment and other consumer |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |
Restructured loans |  |  |  | 16 |  | 32
Nonperforming TDRs |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |
Restructured loans |  |  |  | 7,143 |  | 11,150
Nonperforming TDRs | Commercial real estate |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |
Restructured loans |  |  |  | 1,152 |  | 967
Nonperforming TDRs | Commercial and industrial |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |
Restructured loans |  |  |  | 2,260 |  | 3,197
Nonperforming TDRs | Commercial construction |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |
Restructured loans |  |  |  | 408 |  | 2,413
Nonperforming TDRs | Residential mortgage |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |
Restructured loans |  |  |  | 1,913 |  | 3,585
Nonperforming TDRs | Home equity |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |
Restructured loans |  |  |  | 1,404 |  | 979
Nonperforming TDRs | Installment and other consumer |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |
Restructured loans |  |  |  | 6 |  | 9
Total TDRs |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |
Restructured loans |  |  |  | 29,369 |  | 26,051
Total TDRs | Commercial real estate |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |
Restructured loans |  |  |  | 3,247 |  | 3,546
Total TDRs | Commercial and industrial |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |
Restructured loans |  |  |  | 14,134 |  | 7,143
Total TDRs | Commercial construction |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |
Restructured loans |  |  |  | 2,808 |  | 4,833
Total TDRs | Residential mortgage |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |
Restructured loans |  |  |  | 4,142 |  | 5,624
Total TDRs | Home equity |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |
Restructured loans |  |  |  | 5,016 |  | 4,864
Total TDRs | Installment and other consumer |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |
Restructured loans |  |  |  | $ 22 |  | $ 41
[1] | Excludes loans that were fully paid off or fully charged-off by period end. The pre-modification balance represents the balance outstanding prior to modification. The post-modification balance represents the outstanding balance at period end.

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