Share-Based Compensation - Stock Option Activity (Details) - Options to purchase common stock - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	9 Months Ended
	Sep. 30, 2020
Number of Shares
Options outstanding (in shares)	16,724
Options, Granted (in shares)	4,282
Options, Exercised (in shares)	(2,849)
Options, Forfeited (in shares)	(1,308)
Options, Expired (in shares)	(434)
Options outstanding (in shares)	16,415
Options, Vested and unvested expected to vest (in shares)	15,492
Options, Exercisable (in shares)	10,150
Weighted Average Exercise  Price
Options outstanding (in dollars per share)	$ 9.15
Options, Granted (in dollars per share)	9.78
Options, Exercised (in dollars per share)	7.03
Options, Forfeited (in dollars per share)	10.41
Options, Expired (in dollars per share)	13.33
Options outstanding (in dollars per share)	9.47
Options, Vested and unvested expected to vest (in dollars per share)	9.42
Options, Exercisable (in dollars per share)	$ 8.94
Additional Disclosures
Weighted average remaining contractual life, options outstanding	6 years 3 months 18 days
Weighted average remaining contractual life, options vested and unvested expected to vest	6 years 2 months 12 days
Weighted average remaining contractual life, options exercisable	4 years 10 months 24 days
Aggregate intrinsic value, options outstanding	$ 79.0
Aggregate intrinsic value, vested and unvested expected to vest	75.4
Aggregate intrinsic value, exercisable	$ 54.6