Stock-Based Compensation - Stock Option Activity (Details) - Employee and nonemployee stock options - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Number of options outstanding
Outstanding options as of the beginning of the period (in shares)	7,150,848
Granted (in shares)	534,412
Exercised (in shares)	(669,030)
Forfeited and cancelled (in shares)	(78,260)
Outstanding options as of the end of the period (in shares)	6,937,970
Weighted- average exercise price (Per share)
Outstanding options as of the beginning of the period (in dollars per share)	$ 28.79
Granted (in dollars per share)	121.20
Exercised (in dollars per share)	12.30
Forfeited and cancelled (in dollars per share)	52.44
Outstanding options as of the end of the period (in dollars per share)	$ 37.23
Weighted- average remaining contractual term (In years)
Weighted-average remaining contractual term (in years)	7 years 1 month 28 days	6 years 5 months 19 days
Aggregate intrinsic value	$ 400,612		$ 511,971
Options vested and exercisable and options vested and expected to vest
Options vested and exercisable - number of options outstanding (in shares)	4,545,317
Options vested and exercisable - weighted-average exercise price (in dollars per share)	$ 18.07
Options vested and exercisable - weighted-average remaining contractual term	6 years 4 months 20 days
Options vested and exercisable - aggregate intrinsic value	$ 329,352