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Portfolio loans and allowance for credit losses - Narrative (Details) $ in Thousands | 12 Months Ended
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Dec. 31, 2020 USD ($) loan | Dec. 31, 2019 USD ($) item contract | Dec. 31, 2018 USD ($)
Distributions of portfolio loans |  |  |
Gross interest income that would have been recorded if impaired loans had been current | $ 1,800 | $ 2,300 | $ 1,700
TDRs subsequently classified as non-performing and had payment defaults | loan | 0 |  |
Commercial Loans |  |  |
Distributions of portfolio loans |  |  |
Number of commercial loans in deferral | loan | 98 |  |
Amount of loan in deferrals | $ 208,600 |  |
Personal Loan |  |  |
Distributions of portfolio loans |  |  |
Number of commercial loans in deferral | loan | 351 |  |
Amount of loan in deferrals | $ 47,700 |  |
Home Equity Loan |  |  |
Distributions of portfolio loans |  |  |
Number of commercial loans in deferral | loan | 1 |  |
Amount of loan in deferrals | $ 100 |  |
Commercial Loans |  |  |
Distributions of portfolio loans |  |  |
Performing loans classified as TDRs | loan | 3 |  |
Commercial Real Estate Loans |  |  |
Distributions of portfolio loans |  |  |
TDRs subsequently classified as non-performing and had payment defaults | contract |  | 1 |
Maximum | Commercial Real Estate Loans |  |  |
Distributions of portfolio loans |  |  |
Limit where loans are processed through an expedited underwriting process | $ 1,000 |  |
Watch | Commercial Loans |  |  |
Distributions of portfolio loans |  |  |
Limit above which loans are annually reviewed | 1,000 |  |
Special Mention |  |  |
Distributions of portfolio loans |  |  |
Limit above which loans are annually reviewed | 350 |  |
In compliance with modified terms | Retail Real Estate |  |  |
Distributions of portfolio loans |  |  |
Number of retail real estate modifications | item |  | 1 |
Loans classified as a TDR | $ 800 | $ 300 |

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