Stock-Based Compensation - Stock Options (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares
Stock Based Compensation
RSUs granted (in shares)	(6,204,000)
RSUs forfeited/cancelled (in shares)	436,000
Additional disclosures
RSUs granted, impact on shares available for grant pool, ratio	2
Employee and non-employee stock options
Stock Based Compensation
Shares available for grant, beginning balance	6,416,000
Additional shares authorized	3,120,000
Options granted (in shares)	(457,000)
Options forfeited (in shares)	155,000
Shares available for grant, end balance	3,466,000	6,416,000
Number of shares
Outstanding, beginning balance (in shares)	8,497,000
Options granted (in shares)	457,000
Options exercised (in shares)	(2,092,000)
Options forfeited (in shares)	(155,000)
Outstanding, end balance (in shares)	6,707,000	8,497,000
Exercisable (in shares)	5,080,000
Vested and expected to vest (in shares)	6,609,000
Weighted-Average Exercise Price
Outstanding, beginning balance (in dollars per share) | $ / shares	$ 10.39
Granted (in dollars per share) | $ / shares	27.67
Exercised (in dollars per share) | $ / shares	11.24
Forfeited (in dollars per share) | $ / shares	15.39
Outstanding, end balance (in dollars per share) | $ / shares	11.19	$ 10.39
Exercisable (in dollars per share) | $ / shares	9.04
Vested and expected to vest (in dollars per share) | $ / shares	$ 11.09
Additional disclosures
Weighted average contractual term, options outstanding	6 years 14 days	6 years 10 months 17 days
Exercisable (in years)	5 years 4 months 24 days
Vested and expected to vest (in years)	6 years 3 days
Aggregate intrinsic value, options outstanding | $	$ 592,468	$ 197,955
Aggregate intrinsic value, options exercisable | $	459,683
Aggregate intrinsic value, vested and expected to vest | $	584,396
Aggregate intrinsic value, options exercised | $	184,700	70,000	$ 25,600
Fair value, options vested | $	$ 52,500	$ 11,000	$ 11,300
Weighted-average grant date fair value, options granted | $ / shares	$ 27.70	$ 8.01	$ 4.85
Non-employee stock options
Stock Based Compensation
Options granted (in shares)	(45,577)
Number of shares
Options granted (in shares)	45,577
Additional disclosures
Options unvested (in shares)	5,366
Restricted stock units
Stock Based Compensation
RSUs granted (in shares)	(3,102)
RSUs forfeited/cancelled (in shares)	218