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Stock-Based Compensation and Employee Benefit Plan - Employee Stock Purchase Plan (Details) - USD ($)
12 Months Ended
Jul. 14, 2018
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Jul. 25, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Allocated share-based compensation expense   $ 180,300,000 $ 30,500,000 $ 28,200,000  
Employee Stock          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Number of share maximum per employee   2,500      
Dollar maximum per employee   $ 25,000      
Offering share price (in dollars per share) $ 15.00        
Allocated share-based compensation expense $ 4,600,000        
2018 ESPP | Employee Stock | Class A common stock          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Shares reserved for future issuance (in shares)         3,333,333
Number of common stock reserved for issuance (in shares)   33,333,333      
Purchase price of common stock, percentage of fair market value   85.00%