Equity Award Plan Activities - Option Activity Rollforward (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Number of Shares Underlying Outstanding Options
Outstanding, beginning balance (in shares)	9,509
Options granted (in shares)	170
Options exercised (in shares)	(2,260)
Options canceled (in shares)	(395)
Outstanding, ending balance (in shares)	7,024	9,509
Vested and exercisable (in shares)	2,992
Vested and expected to vest (in shares)	7,024
Weighted- Average Exercise Price per Share
Outstanding, beginning balance (in dollars per share)	$ 28.79
Options granted (in dollars per share)	96.60
Options exercised (in dollars per share)	19.73
Options canceled (in dollars per share)	34.04
Outstanding, ending balance (in dollars per share)	33.05	$ 28.79
Vested and exercisable (in dollars per share)	20.70
Vested and expected to vest (in dollars per share)	$ 33.05
Weighted- Average Remaining Contractual Term (Years) and Aggregate Intrinsic Value of Stock Options
Weighted-average remaining contractual term of stock options outstanding	6 years 1 month 2 days	6 years 11 months 1 day
Weighted-average remaining contractual term of stock options vested and exercisable	5 years 5 months 8 days
Weighted-average remaining contractual term of stock options vested and expected to vest	6 years 1 month 2 days
Aggregate intrinsic value of stock options outstanding	$ 1,422,637	$ 646,394
Aggregate intrinsic value of stock options outstanding vested and exercisable	643,012
Aggregate intrinsic value of stock options outstanding vested and expected to vest	$ 1,422,637