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, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Numerator:
Net loss, basic and diluted	$ (27,732)	$ (23,156)	$ (63,693)	$ (31,841)
Denominator:
Weighted-average shares outstanding	53,088	51,445	52,924	51,124
Less: weighted-average unvested shares subject to repurchase				(182)
Weighted-average number of shares used in computing net loss per share, basic and diluted	53,088	51,445	52,924	50,942
Net loss per share, basic and diluted (in dollars per share)	$ (0.52)	$ (0.46)	$ (1.20)	$ (0.63)