Stock-based Awards - Schedule of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Number of Options
Outstanding at the end of the period (in shares)	16,714,216
Options to Purchase Common Stock
Number of Options
Outstanding at the beginning of period (in shares)	24,541,512
Granted (in shares)	4,846,453
Exercised (in shares)	(11,650,950)
Canceled/forfeited (in shares)	(1,022,799)
Outstanding at the end of the period (in shares)	16,714,216	24,541,512
Vested and expected to vest at the end of the period (in shares)	16,714,216
Exercisable at the end of the period (in shares)	8,005,880
Weighted-Average Exercise Price
Outstanding at the beginning of period (in dollars per share)	$ 8.29
Granted (in dollars per share)	18.38
Exercised (in dollars per share)	6.31
Canceled/forfeited (in dollars per share)	10.49
Outstanding at the end of the period (in dollars per share)	12.46	$ 8.29
Vested and expected to vest at the end of the period (in dollars per share)	12.46
Exercisable at the end of the period (in dollars per share)	$ 10.73
Weighted-Average Remaining Contractual Life
Outstanding at the end of the period	7 years 8 months 12 days	5 years 5 months 27 days
Vested and expected to vest at the end of the period	7 years 8 months 12 days
Exercisable at the end of the period	6 years 6 months
Aggregate Intrinsic Value
Intrinsic value of all outstanding options	$ 21.7
Intrinsic value of options vested and expected to vest	21.7
Intrinsic value of exercisable options	$ 13.5