v3.19.2
Stockholders' Equity - Summary of Stock Option Award Activity (Details) - Stock Options - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
 6 Months Ended 12 Months Ended
Jun. 30, 2019
Dec. 31, 2018
Weighted-Average Exercise Price    
Weighted-Average Exercise Price, Beginning balance $ 7.83  
Weighted-Average Exercise Price, Exercised 2.76  
Weighted-Average Exercise Price, Forfeited 13.89  
Weighted-Average Exercise Price, Ending balance $ 8.22 $ 7.83
Weighted-Average Remaining Contractual Term    
Weighted-Average Remaining Contractual Term (in years) 5 years 9 months 7 days 6 years 4 months 28 days
Aggregate Intrinsic Value    
Aggregate Intrinsic Value, Outstanding $ 34,567  
Aggregate Intrinsic Value, Outstanding $ 78,348 $ 34,567
Class A Common Stock    
Number of Shares    
Number of Shares, Beginning balance 13,322  
Number of Shares, Exercised (1,724)  
Number of Shares, Forfeited (1,257)  
Number of Shares, Ending balance 10,341 13,322
Class B Common Stock    
Number of Shares    
Number of Shares, Beginning balance 2,969  
Number of Shares, Exercised (790)  
Number of Shares, Forfeited (29)  
Number of Shares, Ending balance 2,150 2,969