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Basis of presentation - Additional Information (Details) $ in Thousands | 9 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Sep. 30, 2020 USD ($) branch | Dec. 31, 2019 USD ($) | Nov. 06, 2020 USD ($)
Class of Stock [Line Items] |  |  |
Number of full-service branches | branch | 87 |  |
Loans processed | $ 310,719 |  |
Stockholders' equity | 1,244,998 | $ 762,329 |
90 Day Fixed Rate Advance |  |  |
Class of Stock [Line Items] |  |  |
Repayments of advances | 100,000 | 100,000 |
90 Day Fixed Rate Advance | Subsequent Event |  |  |
Class of Stock [Line Items] |  |  |
Amount not elected for renewal |  |  | $ 100,000
Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent |  |  |
Class of Stock [Line Items] |  |  |
Stockholders' equity | $ 545 | $ 955 |

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