Net Loss per Share - Loss per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Numerator:
Net loss	$ (35,961)	$ (8,685)
Remeasurement gain on warrant liability	(1,042)
Net loss used to compute net loss per share, diluted	$ (37,003)	$ (8,685)
Denominator:
Weighted-average common shares outstanding	52,758	50,803
Less: weighted-average unvested common shares subject to repurchase		(364)
Weighted-average number of shares used in computing net loss per share, basic	52,758	50,439
Add: incremental shares from assumed exercise of warrants	285
Weighted-average number of shares used in computing net loss per share, diluted	53,043	50,439
Net loss per share, basic (in dollars per share)	$ (0.68)	$ (0.17)
Net loss per share, diluted (in dollars per share)	$ (0.70)	$ (0.17)