Notes Payable - Schedule of Stated Maturities of Notes Payable (Details) - USD ($) $ in Thousands |
Sep. 30, 2021 |
Dec. 31, 2020 |
Dec. 31, 2018 |
|---|---|---|---|
| Debt Disclosure [Abstract] | |||
| 2021 | $ 2,000 | ||
| 2022 | 4,000 | $ 2,000 | |
| 2022 | 4,000 | ||
| Total notes payable | $ 6,000 | $ 6,000 | $ 6,000 |