Net Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Numerator:
Net loss	$ (67,180)	$ (84,482)	$ (61,889)
Denominator:
Weighted-average shares outstanding	85,853	78,867	48,332
Less: weighted average shares subject to repurchase	(8)	(112)	(815)
Weighted-average shares used to compute basic and diluted net loss per share	85,845	78,755	47,517
Basic and diluted net loss per share	$ (0.78)	$ (1.07)	$ (1.30)