Stock-Based Compensation - Stock Option Activity (Details) - Employee and nonemployee stock options - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Number of options outstanding
Outstanding options as of the beginning of the period (in shares)	7,423,369
Granted (in shares)	909,229
Assumed in acquisition (in shares)	2,978,555
Exercised (in shares)	(3,620,866)
Forfeited and cancelled (in shares)	(539,439)
Outstanding options as of the end of the period (in shares)	7,150,848	7,423,369
Weighted- average exercise price (Per share)
Outstanding options as of the beginning of the period (in dollars per share)	$ 16.07
Granted (in dollars per share)	118.35
Assumed in acquisition (in dollars per share)	14.91
Exercised (in dollars per share)	10.43
Forfeited and cancelled (in dollars per share)	51.28
Outstanding options as of the end of the period (in dollars per share)	$ 28.79	$ 16.07
Weighted- average remaining contractual term (in years)
Weighted-average remaining contractual term (in years)	6 years 5 months 19 days	6 years 9 months 18 days
Aggregate intrinsic value	$ 511,971	$ 543,640
Options vested and exercisable and options vested and expected to vest
Options vested and exercisable - number of options outstanding (in shares)	4,721,801
Options vested and exercisable - weighted-average exercise price (in dollars per share)	$ 14.00
Options vested and exercisable - weighted-average remaining contractual term	5 years 7 months 24 days
Options vested and exercisable - aggregate intrinsic value	$ 398,490