Notes Payable Related Party - Summary of Stated Maturities of Notes Payable to Related Parties (Details) - USD ($) $ in Thousands |
Sep. 30, 2021 |
Dec. 31, 2020 |
Dec. 31, 2019 |
Dec. 31, 2018 |
|---|---|---|---|---|
| Notes Payable Related Party [Abstract] | ||||
| 2022/2021 | $ 12,000 | $ 12,011 | ||
| Notes payable due to related parties | $ 12,000 | $ 12,011 | $ 12,952 | $ 14,215 |