Stock-Based Compensation - Stock Options (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Stock Based Compensation
RSUs granted (in shares)	(4,140)
RSUs forfeited/cancelled (in shares)	88
Employee and non-employee stock options
Stock Based Compensation
Shares available for grant, beginning balance	6,416
Additional shares authorized	3,120
Options granted (in shares)	(409)
Options forfeited (in shares)	45
Shares available for grant, end balance	5,120	6,416
Number of shares
Outstanding, beginning balance (in shares)	8,497
Options granted (in shares)	409
Options exercised (in shares)	(356)
Options forfeited (in shares)	(45)
Outstanding, end balance (in shares)	8,505	8,497
Exercisable (in shares)	5,078
Vested and expected to vest (in shares)	8,316
Weighted-Average Exercise Price
Outstanding, beginning balance (in dollars per share)	$ 10.39
Granted (in dollars per share)	25.51
Exercised (in dollars per share)	10.74
Forfeited (in dollars per share)	17.76
Outstanding, end balance (in dollars per share)	11.07	$ 10.39
Exercisable (in dollars per share)	7.85
Vested and expected to vest (in dollars per share)	$ 10.96
Additional disclosures
Weighted average contractual term, options outstanding	6 years 9 months 10 days	6 years 10 months 17 days
Exercisable (in years)	5 years 6 months 14 days
Vested and expected to vest (in years)	6 years 8 months 26 days
Aggregate intrinsic value, options outstanding	$ 159,957	$ 197,955
Aggregate intrinsic value, options exercisable	111,759
Aggregate intrinsic value, vested and expected to vest	$ 157,297
Restricted stock units
Stock Based Compensation
RSUs granted (in shares)	(2,071)
RSUs forfeited/cancelled (in shares)	44