Stock-Based Compensation - Stock Options (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Weighted-average price per share
Allocated Share-based Compensation Expense	$ 25,016	$ 12,919	$ 66,925	$ 34,064
Outstanding stock options and Employee Stock Purchase Plan
Shares
Outstanding at the beginning of the period (in shares)			6,978,621
Granted (in shares)			674,707
Exercised (in shares)			(552,720)
Cancelled (in shares)			(86,563)
Outstanding at the end of the period (in shares)	7,014,045		7,014,045
Vested at the end of the period (in shares)			3,987,711
Weighted-average price per share
Outstanding at the beginning of the period (in dollars per share)			$ 40.65
Granted (in dollars per share)			162.02
Exercised (in dollars per share)			43.10
Cancelled (in dollars per share)			57.98
Outstanding at the end of the period (in dollars per share)	$ 51.92		51.92
Vested at the end of the period (in dollars per share)	$ 30.94		$ 30.94
Total unrecognized compensation cost related to unvested stock options (in dollars)	$ 127,100		$ 127,100
Weighted average period over which unrecognized compensation costs are expected to be recognized	2 years 3 months 18 days