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Stock-Based Compensation (Details) - shares
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Share-based compensation        
Stock Awards Outstanding (in shares) 17,403,339      
Percentage of stock awards vesting per year 20.00%      
Class A common stock        
Share-based compensation        
Stock Awards Outstanding (in shares) 27,200,000      
Class A common stock | Stock Incentive Plan [Member]        
Share-based compensation        
Shares of common stock available for future grant under stock incentive plans 63,600,000      
Stock options        
Share-based compensation        
Stock Awards Outstanding (in shares) 27,248,662 13,715,612 14,202,039 8,847,734
Maximum Expiration term 10 years