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, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Basic and diluted loss per share:
Net loss	$ (23,156)	$ (19,681)	$ (31,841)	$ (29,685)
Weighted-average common shares outstanding	51,445	7,026	51,124	6,971
Less: weighted-average unvested common shares subject to repurchase		(1,532)	(182)	(1,578)
Weighted-average number of shares used in computing net loss per share, basic and diluted	51,445	5,494	50,942	5,393
Basic and diluted net loss per share (in dollars per share)	$ (0.46)	$ (3.58)	$ (0.63)	$ (5.50)