Net Loss per Share - Loss per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Numerator:
Net loss used to compute net loss per share, basic	$ (33,824)	$ (29,066)	$ (66,697)	$ (62,546)
Denominator:
Weighted-average number of shares used in computing net loss per share, basic	54,551	53,088	54,342	52,924
Net loss per share, basic (in dollars per share)	$ (0.62)	$ (0.55)	$ (1.23)	$ (1.18)
Net loss per share, diluted (in dollars per share)	$ (0.62)	$ (0.55)	$ (1.23)	$ (1.18)