Significant Accounting Policies - Equity-Based Compensation (Details) - shares |
Sep. 30, 2021 |
Dec. 31, 2020 |
Sep. 30, 2020 |
Apr. 16, 2020 |
Dec. 31, 2019 |
Dec. 31, 2018 |
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| Equity-Based Compensation | ||||||
| Maximum aggregate incentive units authorized for issuance | 1,045,000 | 1,550,000 | 1,550,000 | 6,845,297 | 2,500,000 | 2,475,000 |
| X | ||||||||||
- References No definition available.
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| X | ||||||||||
- Definition Number of shares authorized for issuance under share-based payment arrangement. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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