Net Loss per Share - Loss per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Numerator:
Net loss, basic and diluted	$ (34,091)	$ (32,873)
Denominator:
Weighted-average number of shares used in computing net loss per share, basic and diluted	62,831	54,132
Net loss per share, basic (in dollars per share)	$ (0.54)	$ (0.61)
Net loss per share, diluted (in dollars per share)	$ (0.54)	$ (0.61)