Stock-Based Awards - Summary of Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2017
Number of Shares
Outstanding, beginning balance, number of shares (in shares)	5,787,151
Granted (in shares)	3,067,718
Exercised (in shares)	(1,504,583)	0
Forfeited/Expired (in shares)	(599,347)
Outstanding, ending balance, number of shares (in shares)	6,750,939
Options vested and expected to vest (in shares)	6,750,939
Options exercisable (in shares)	3,052,876
Weighted Average Exercise Price
Outstanding, beginning balance (in dollars per share)	$ 10.92
Granted (in dollars per share)	28.77
Exercised (in dollars per share)	4.49
Forfeited/Expired (in dollars per share)	23.40
Outstanding, ending balance (in dollars per share)	19.36
Options vested and expected to vest (in dollars per share)	19.36
Options exercisable (in dollars per share)	$ 10.62
Additional Disclosures
Outstanding, weighted average remaining contractual term	8 years
Options vested and expected to vest, weighted average remaining contractual term	8 years
Options exercisable, weighted average remaining contractual term	6 years 10 months 24 days
Outstanding, aggregate intrinsic value	$ 289,615
Options vested and expected to vest, aggregate intrinsic value	289,615
Options exercisable, aggregate intrinsic value	$ 157,592