Net Loss Per Share Attributable to Common Stockholders - Computation of Basic and Diluted 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 attributable to common stockholders	$ (5,171)	$ (8,755)	$ (18,731)	$ (23,636)
Denominator:
Weighted-average common shares outstanding - basic and diluted	40,120	13,884	39,240	13,307
Net loss per common share - basic and diluted	$ (0.13)	$ (0.63)	$ (0.48)	$ (1.78)