Stock-Based Compensation - Option and RSA Activity Rollforward (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Shares Available for Grant
Shares available for grant beginning balance (in shares)	11,612
Options granted (in shares)	(1,035)
Early exercised shares repurchased (in shares)	13
Shares available for grant ending balance (in shares)	11,294	11,612
Number of Shares Underlying Outstanding Options and RSAs (in thousands)
Beginning balance, options (in shares)	13,654
Options granted (in shares)	1,035
Options exercised (in shares)	(1,654)
Options canceled (in shares)	(704)
Early exercised shares repurchased (in shares)	0
Ending balance, options (in shares)	12,331	13,654
Vested and exercisable (in shares)	3,170
Vested and expected to vest (in shares)	10,941
Weighted- Average Exercise Price per Share
Outstanding beginning balance (usd per share)	$ 17.63
Options granted (usd per share)	66.80
Options exercised (usd per share)	7.28
Options canceled (usd per share)	19.50
Early exercised shares repurchased	3.98
Outstanding ending balance (usd per share)	23.03	$ 17.63
Vested and exercisable (usd per share)	7.21
Vested and expected to vest (usd per share)	$ 21.62
Weighted- Average Remaining Contractual Term and Aggregate Intrinsic Value of Stock Options Outstanding
SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2	8 years 1 month 16 days	8 years 3 months 18 days
Weighted-average remaining contractual term of stock options vested and exercisable	7 years
Weighted-average remaining contractual term of stock options vested and expected to vest	8 years
Aggregate intrinsic value of stock options outstanding	$ 697,621	$ 598,775
Aggregate intrinsic value of stock options outstanding vested and exercisable	236,274
Aggregate intrinsic value of stock options outstanding vested and expected to vest	$ 657,910