v3.19.3
Stockholders' Equity - Summary of Stock Option Award Activity (Details) - Stock Options - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
 9 Months Ended 12 Months Ended
Sep. 30, 2019
Dec. 31, 2018
Weighted-Average Exercise Price    
Weighted-Average Exercise Price, Beginning balance $ 7.83  
Weighted-Average Exercise Price, Granted 14.69  
Weighted-Average Exercise Price, Exercised 3.52  
Weighted-Average Exercise Price, Forfeited 13.88  
Weighted-Average Exercise Price, Ending balance $ 8.82 $ 7.83
Weighted-Average Remaining Contractual Term    
Weighted-Average Remaining Contractual Term (in years) 5 years 9 months 18 days 6 years 4 months 28 days
Aggregate Intrinsic Value    
Aggregate Intrinsic Value, Outstanding $ 34,567  
Aggregate Intrinsic Value, Outstanding $ 76,421 $ 34,567
Class A Common Stock    
Number of Shares    
Number of Shares, Beginning balance 13,322  
Number of Shares, Granted 118  
Number of Shares, Exercised (3,024)  
Number of Shares, Forfeited (1,302)  
Number of Shares, Ending balance 9,114 13,322
Class B Common Stock    
Number of Shares    
Number of Shares, Beginning balance 2,969  
Number of Shares, Exercised (1,162)  
Number of Shares, Forfeited (29)  
Number of Shares, Ending balance 1,778 2,969