Net Loss per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Numerator:
Net loss	$ (17,065)	$ (14,593)	$ (48,442)	$ (56,974)
Denominator:
Weighted-average shares outstanding	95,024	86,714	92,826	85,017
Less: weighted average shares subject to repurchase		(1)	(1)	(9)
Weighted-average shares used to compute basic and diluted net loss per share	95,024	86,713	92,825	85,008
Basic and diluted net loss per share	$ (0.18)	$ (0.17)	$ (0.52)	$ (0.67)