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Long-Term Debt - Additional Information (Details) - Promissory Notes Payable $ in Thousands | 9 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | ---
Sep. 30, 2021 USD ($) | Dec. 31, 2019 | Dec. 31, 2020 USD ($) | Jan. 01, 2019 USD ($) Installment
Debt Instrument [Line Items] |  |  |  |
Debt instrument, outstanding balance | $ | $ 251 |  | $ 362 | $ 736
Debt instrument, periodic payment, number of equal quarterly installments | Installment |  |  |  | 20
Debt instrument, frequency of periodic payment |  | quarterly |  |
Minimum |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Debt instrument, payment term | 2 years |  |  |
Maximum |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Debt instrument, payment term | 4 years |  |  |
Interest rate, stated percentage | 8.00% |  |  |

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