Stock-based Compensation - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Shares
Outstanding, beginning balance (in shares)	6,890,994	7,947,939	9,339,567
Granted (in shares)	462,563	797,201	5,887,183
Exercised (in shares)	(840,835)	(1,588,779)	(5,760,263)
Forfeited/Cancelled (in shares)	(217,803)	(265,367)	(1,518,548)
Outstanding, ending balance (in shares)	6,294,919	6,890,994	7,947,939	9,339,567
Total exercisable at December 31, 2019, Shares (in shares)	3,835,279
Weighted-Average Exercise Price
Outstanding, beginning balance (in dollars per share)	$ 12.91	$ 11.02	$ 7.89
Granted (in dollars per share)	64.29	29.87	11.04
Exercised (in dollars per share)	11.64	11.49	5.87
Forfeited/Cancelled (in dollars per share)	30.11	15.68	11.36
Outstanding, ending balance (in dollars per share)	16.26	$ 12.91	$ 11.02	$ 7.89
Total exercisable at December 31, 2019, Weighted-Average Exercise Price (in dollars per share)	$ 12.30
Weighted-Average Remaining Contract Term (in years)
Outstanding at December 31, 2019	7 years 2 months 26 days	7 years 11 months 8 days	7 years 11 months 4 days	6 years 7 months 20 days
Total exercisable at December 31, 2019	6 years 10 months 17 days
Aggregate Intrinsic Value
Outstanding at December 31, 2019	$ 185,900	$ 239,177	$ 74,996	$ 43,613
Total exercisable at December 31, 2019	$ 123,671