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, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Numerator:
Net loss attributable to common stockholders	$ (8,755)	$ (9,865)	$ (23,636)	$ (28,271)
Denominator:
Weighted-average common shares outstanding - basic and diluted	13,884	12,754	13,307	12,575
Net loss per common share, basic and diluted	$ (0.63)	$ (0.77)	$ (1.78)	$ (2.25)