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Loans and Loans Held for Sale - Summary of Restructured Loans (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2018 | Mar. 31, 2017 | Dec. 31, 2017
Financing Receivable, Modifications [Line Items] |  |  |  |
Restructured loans | [1] | $ 6,770 | $ 438 |
Commercial and industrial |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |
Restructured loans | [1] | 6,041 | 0 |
Commercial construction |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |
Restructured loans | [1] | 157 | 0 |
Home equity |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |
Restructured loans | [1] | 555 | 438 |
Installment and other consumer |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |
Restructured loans |  | 17 | $ 0 |
Performing TDRs |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |
Restructured loans |  | 20,035 |  | $ 14,901
Performing TDRs | Commercial real estate |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |
Restructured loans |  | 2,298 |  | 2,579
Performing TDRs | Commercial and industrial |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |
Restructured loans |  | 9,403 |  | 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 |  | 2,178 |  | 2,039
Performing TDRs | Home equity |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |
Restructured loans |  | 3,713 |  | 3,885
Performing TDRs | Installment and other consumer |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |
Restructured loans |  | 43 |  | 32
Nonperforming TDRs |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |
Restructured loans |  | 8,560 |  | 11,150
Nonperforming TDRs | Commercial real estate |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |
Restructured loans |  | 944 |  | 967
Nonperforming TDRs | Commercial and industrial |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |
Restructured loans |  | 3,036 |  | 3,197
Nonperforming TDRs | Commercial construction |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |
Restructured loans |  | 414 |  | 2,413
Nonperforming TDRs | Residential mortgage |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |
Restructured loans |  | 2,640 |  | 3,585
Nonperforming TDRs | Home equity |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |
Restructured loans |  | 1,520 |  | 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 |  | 28,595 |  | 26,051
Total TDRs | Commercial real estate |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |
Restructured loans |  | 3,242 |  | 3,546
Total TDRs | Commercial and industrial |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |
Restructured loans |  | 12,439 |  | 7,143
Total TDRs | Commercial construction |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |
Restructured loans |  | 2,814 |  | 4,833
Total TDRs | Residential mortgage |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |
Restructured loans |  | 4,818 |  | 5,624
Total TDRs | Home equity |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |
Restructured loans |  | 5,233 |  | 4,864
Total TDRs | Installment and other consumer |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |
Restructured loans |  | $ 49 |  | $ 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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