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Stockholders' Equity Share Activity by Class (Details) - shares | 12 Months Ended |
--- | --- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Class of Stock [Line Items] |  |  |  |
Stock Issued During Period, Shares, New Issues | (24,233) |  |  |
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation | (126,971) | (82,729) | (77,442) |
Outstanding | 78,572,110 | 77,801,854 | 76,942,872 | 75,569,845
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number | 304,570 | 297,891 | 246,581 |
Class A Common Stock |  |  |  |
Class of Stock [Line Items] |  |  |  |
Stock Issued During Period, Shares, New Issues | (24,233) |  |  |
Shares repurchased and retired during the period (shares) | (43,091) |  |  |
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation | (126,971) | (82,729) | (77,442) |
Outstanding | 63,131,007 | 56,429,825 | 54,071,188 | 50,463,126
Class B Common Stock |  |  |  |
Class of Stock [Line Items] |  |  |  |
Stock Issued During Period, Shares, New Issues | (1,777,326) |  | (644,424) |
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation | 0 | 0 | 0 |
Outstanding | 4,457,958 | 7,803,364 | 8,645,249 | 11,922,192
Class C Common Stock |  |  |  |
Class of Stock [Line Items] |  |  |  |
Stock Issued During Period, Shares, New Issues | (25,000) |  | 0 |
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation | 0 | 0 | 0 |
Outstanding | 10,983,145 | 13,568,665 | 14,226,435 | 13,184,527
Common Stock |  |  |  |
Class of Stock [Line Items] |  |  |  |
Shares repurchased and retired during the period (shares) | (43,091) | (17,289) | (67,255) |
Common Stock | Class A Common Stock |  |  |  |
Class of Stock [Line Items] |  |  |  |
Shares repurchased and retired during the period (shares) |  | (17,289) | (67,255) |
Common Stock | Class B Common Stock |  |  |  |
Class of Stock [Line Items] |  |  |  |
Shares repurchased and retired during the period (shares) | (32,805) | 0 | (2,026,453) |
Common Stock | Class C Common Stock |  |  |  |
Class of Stock [Line Items] |  |  |  |
Stock Issued During Period, Shares, New Issues | (32,805) | 0 | (2,026,453) |
Common Stock | Class A Common Stock |  |  |  |
Class of Stock [Line Items] |  |  |  |
Shares repurchased and retired during the period (shares) |  | (1,499,655) | (1,590,611) |
Common Stock | Class B Common Stock |  |  |  |
Class of Stock [Line Items] |  |  |  |
Shares repurchased and retired during the period (shares) | (1,535,275) | (841,885) | (606,066) |
Common Stock | Class C Common Stock |  |  |  |
Class of Stock [Line Items] |  |  |  |
Shares repurchased and retired during the period (shares) | (2,593,325) | (657,770) | (984,545) |
Unvested restricted share-based awards |  |  |  |
Class of Stock [Line Items] |  |  |  |
Stock Issued During Period, Shares, New Issues | (916,085) | (959,000) | (1,517,724) |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number | 5,293,642 | 5,005,422 | 4,678,457 | 4,013,986
Unvested restricted share-based awards | Class A Common Stock |  |  |  |
Class of Stock [Line Items] |  |  |  |
Stock Issued During Period, Shares, New Issues | (916,085) | (959,000) | (1,517,724) |
Unvested restricted share-based awards | Class B Common Stock |  |  |  |
Class of Stock [Line Items] |  |  |  |
Shares repurchased and retired during the period (shares) | 0 | 0 | 0 |
Unvested restricted share-based awards | Class C Common Stock |  |  |  |
Class of Stock [Line Items] |  |  |  |
Shares repurchased and retired during the period (shares) | 0 | 0 | 0 |
Performance Shares |  |  |  |
Class of Stock [Line Items] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number | 60,000 | 0 |  |
Performance Shares | Pro Forma |  |  |  |
Class of Stock [Line Items] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number | 90,000 |  |  |

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