Investment securities - schedule of Net Investment Income (Details) - USD ($) $ in Thousands |
3 Months Ended | 9 Months Ended | 12 Months Ended | |||
|---|---|---|---|---|---|---|
Sep. 30, 2021 |
Sep. 30, 2020 |
Sep. 30, 2021 |
Sep. 30, 2020 |
Dec. 31, 2020 |
Dec. 31, 2019 |
|
| Fair Value, Separate Account Investment [Line Items] | ||||||
| Net investment income | $ 179 | $ 823 | $ 340 | $ 2,226 | $ 2,976 | $ 4,539 |
| Cash and cash equivalents | ||||||
| Fair Value, Separate Account Investment [Line Items] | ||||||
| Net investment income | 0 | 1 | 0 | 108 | 108 | 1,249 |
| Short-term investments | ||||||
| Fair Value, Separate Account Investment [Line Items] | ||||||
| Net investment income | 62 | 519 | 139 | 1,141 | 1,722 | 2,904 |
| Investment securities | ||||||
| Fair Value, Separate Account Investment [Line Items] | ||||||
| Net investment income | $ 117 | $ 303 | $ 201 | $ 977 | $ 1,146 | $ 386 |