Net Loss Per Share - Schedule of Outstanding Common Equivalent Shares Excluded from Computation of Diluted Net Loss Per Share (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Outstanding common equivalent shares	26,307	15,486
Stock Options and ESPP
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Outstanding common equivalent shares	8,071	8,531
Restricted Stock Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Outstanding common equivalent shares	5,715	4,955
Shares Held in Escrow
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Outstanding common equivalent shares	1,000	2,000
Shares Related to Convertible Senior Notes
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Outstanding common equivalent shares	11,521