Stockholders' Equity - Stock Options Activity and Status (Details) - Stock Options - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Number of Options
Outstanding at the beginning of the period (in shares)			4,459,291
Granted (in shares)			1,958,843
Exercised (in shares)	(40,565)	(42,443)	(428,541)	(196,984)
Forfeited/canceled (in shares)			(64,586)
Outstanding at the end of the period (in shares)	5,925,007		5,925,007
Exercisable at the end of the period (in shares)	3,114,975		3,114,975
Unvested at the end of the period (in shares)	2,810,032		2,810,032
Weighted-Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)			$ 104.97
Granted (in dollars per share)			145.72
Exercised (in dollars per share)			89.17
Forfeited/canceled (in dollars per share)			132.86
Outstanding at the end of the period (in dollars per share)	$ 119.28		119.28
Exercisable at the end of period (in dollars per share)	102.70		102.70
Unvested at the end of period (in dollars per share)	$ 137.66		$ 137.66
Weighted Average Remaining Contractual Term (Years)
Outstanding at the end of the period			7 years 3 months 18 days
Exercisable at the end of the period			5 years 8 months 12 days
Unvested at the end of the period			9 years 1 month 6 days
Aggregate Intrinsic Value
Outstanding at the end of the period (in dollars)	$ 64.4		$ 64.4
Exercisable at the end of the period (in dollars)	63.8		63.8
Unvested at the end of period (in dollars)	$ 0.6		$ 0.6
Weighted average fair value of a stock option (in dollars per share)			$ 56.07	$ 42.55
Aggregate grant date fair value			$ 109.8	$ 69.2
Total fair value of employee stock options that vested			$ 13.1	$ 19.9