Stock-Based Compensation - Stock Options (Details) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares
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)	(457)
Options forfeited (in shares)	155
RSUs granted (in shares)	(5,143)
RSUs forfeited/cancelled (in shares)	427
Shares available for grant, end balance	4,518	6,416
Number of shares
Outstanding, beginning balance (in shares)	8,497
Options granted (in shares)	457
Options exercised (in shares)	(1,534)
Options forfeited (in shares)	(155)
Outstanding, end balance (in shares)	7,265	8,497
Exercisable (in shares)	5,382
Vested and expected to vest (in shares)	7,148
Weighted-Average Exercise Price
Outstanding, beginning balance (in dollars per share) | $ / shares	$ 10.39
Granted (in dollars per share) | $ / shares	27.61
Exercised (in dollars per share) | $ / shares	10.28
Forfeited (in dollars per share) | $ / shares	15.40
Outstanding, end balance (in dollars per share) | $ / shares	11.39	$ 10.39
Exercisable (in dollars per share) | $ / shares	9.34
Vested and expected to vest (in dollars per share) | $ / shares	$ 11.30
Additional disclosures
Weighted average contractual term, options outstanding	6 years 4 months 9 days	6 years 10 months 17 days
Exercisable (in years)	5 years 8 months 15 days
Vested and expected to vest (in years)	6 years 3 months 29 days
Aggregate intrinsic value, options outstanding | $	$ 442,004	$ 197,955
Aggregate intrinsic value, options exercisable | $	338,529
Aggregate intrinsic value, vested and expected to vest | $	$ 435,595
Restricted stock units
Stock Based Compensation
RSUs granted (in shares)	(2,571)
RSUs forfeited/cancelled (in shares)	213
Additional disclosures
RSUs granted, impact on shares available for grant pool, ratio	2