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Stockholders' Equity - Share Activity by Class of Stock - shares | Total | Class A Common Stock | Class B Common Stock | Class C Common Stock | Common Stock | Common Stock Holdings GP Units | Common Stock Class B Common Stock | Common Stock Class C Common Stock | Restricted Stock | Restricted Stock Class A Common Stock | Restricted Stock Class B Common Stock | Restricted Stock Class C Common Stock | Restricted Stock Units RSUs | Common Stock | Common Stock Class A Common Stock | Common Stock Class B Common Stock | Common Stock Class C Common Stock
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Increase (Decrease) in Stockholders' Equity [Roll Forward] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Restricted stock units outstanding (in shares) |  |  |  |  |  |  |  |  |  |  |  |  | 246,581 |  |  |  |
Beginning balance (in shares) at Dec. 31, 2018 | 76,942,872 |  | 8,645,249 | 14,226,435 |  |  |  |  |  |  |  |  |  |  |  |  |
Increase (Decrease) in Stockholders' Equity [Roll Forward] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Holdings Common Unit Exchanges (in shares) |  |  |  |  | 0 | (1,330,432) | (791,885) | (538,547) |  |  |  |  |  |  |  |  |
Shares issued (in shares) |  |  |  |  |  |  |  |  | 959,000 | 959,000 | 0 | 0 |  |  |  |  |
Restricted share award net share settlement (in shares) | (82,729) | (82,729) | 0 | 0 |  |  |  |  |  |  |  |  |  |  |  |  |
Employee/Partner Terminations (in shares) |  |  |  |  |  |  |  |  |  |  |  |  |  | (16,865) | (16,865) | 0 | 0
Ending balance (in shares) at Sep. 30, 2019 | 77,802,278 | 56,261,026 | 7,853,364 | 13,687,888 |  |  |  |  |  |  |  |  |  |  |  |  |
Increase (Decrease) in Stockholders' Equity [Roll Forward] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Restricted stock units outstanding (in shares) |  |  |  |  |  |  |  |  |  |  |  |  | 297,891 |  |  |  |

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