Equity Award Plan Activities - Option Activity Rollforward (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Number of Shares Underlying Outstanding Options
Outstanding, beginning balance (in shares)	7,024
Options granted (in shares)	0
Options exercised (in shares)	(394)
Options canceled (in shares)	(18)
Outstanding, ending balance (in shares)	6,612	7,024
Vested and exercisable (in shares)	2,911
Weighted- Average Exercise Price per Share
Outstanding, beginning balance (in dollars per share)	$ 33.05
Options granted (in dollars per share)	0.00
Options exercised (in dollars per share)	25.39
Options canceled (in dollars per share)	41.58
Outstanding, ending balance (in dollars per share)	33.48	$ 33.05
Vested and exercisable (in dollars per share)	$ 22.71
Weighted- Average Remaining Contractual Term (Years) and Aggregate Intrinsic Value of Stock Options
Weighted-average remaining contractual term of stock options outstanding	5 years 10 months 21 days	6 years 1 month 2 days
Weighted-average remaining contractual term of stock options vested and exercisable	5 years 3 months 25 days
Aggregate intrinsic value of stock options outstanding	$ 1,466,783	$ 1,422,637
Aggregate intrinsic value of stock options outstanding, vested and exercisable	$ 676,982