Net Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerator:
Net loss	$ (48,846)	$ (43,084)	$ (53,362)
Denominator:
Weighted-average shares outstanding	109,973	102,527	93,771
Less: weighted average shares subject to repurchase			(1)
Weighted-average shares used to compute basic and diluted net loss per share	109,973	102,527	93,770
Basic and diluted net loss per share	$ (0.44)	$ (0.42)	$ (0.57)