| Stock-Based Compensation - Incentive Plans and Grants of Stock Awards (Details) | 9 Months Ended | 
|---|---|
| Sep. 30, 2021  $ / shares  shares | |
| Fair value assumptions | |
| Dividend rate | 0.00% | 
| Options | Series A common stock | |
| Stock Based Compensation | |
| Options granted (in shares) | 0 | 
| Options | Series B common stock | |
| Stock Based Compensation | |
| Options granted (in shares) | 0 | 
| Options | Series C | |
| Stock Based Compensation | |
| Options granted (in shares) | 199,000 | 
| Options | CEO | Series C | |
| Stock Based Compensation | |
| Options granted (in shares) | 167,000 | 
| Options grant date fair value | $ / shares | $ 40.05 | 
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- Definition The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available. 
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- Definition Gross number of share options (or share units) granted during the period. No definition available. 
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- Definition The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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