Share-Based Compensation - Stock Option Activity (Details) - Options to purchase common stock $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($) $ / shares shares
Number of Shares
Options outstanding (in shares) | shares	16,724
Options, Granted (in shares) | shares	3,944
Options, Exercised (in shares) | shares	(968)
Options, Forfeited (in shares) | shares	(355)
Options, Expired (in shares) | shares	(259)
Options outstanding (in shares) | shares	19,086
Options, Vested and unvested expected to vest (in shares) | shares	17,629
Options, Exercisable (in shares) | shares	10,808
Weighted Average Exercise  Price
Options outstanding (in dollars per share) | $ / shares	$ 9.15
Options, Granted (in dollars per share) | $ / shares	9.57
Options, Exercised (in dollars per share) | $ / shares	6.28
Options, Forfeited (in dollars per share) | $ / shares	10.40
Options, Expired (in dollars per share) | $ / shares	13.08
Options outstanding (in dollars per share) | $ / shares	9.30
Options, Vested and unvested expected to vest (in dollars per share) | $ / shares	9.23
Options, Exercisable (in dollars per share) | $ / shares	$ 8.59
Additional Disclosures
Weighted average remaining contractual life, options outstanding	7 years
Weighted average remaining contractual life, options vested and unvested expected to vest	6 years 9 months 18 days
Weighted average remaining contractual life, options exercisable	5 years 4 months 24 days
Aggregate intrinsic value, options outstanding | $	$ 23.5
Aggregate intrinsic value, vested and unvested expected to vest | $	23.4
Aggregate intrinsic value, exercisable | $	$ 21.4