Net Loss Per Share Available to Common Stockholders - Calculation of Basic and Diluted Net Loss Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Numerator:
Net loss available to common stockholders	$ (6,126)	$ (4,413)
Denominator:
Weighted average number of shares, basic and diluted	39,081	37,767
Net loss per share available to common stockholders
Basic and diluted net loss per common share available to common stockholders	$ (0.16)	$ (0.12)