Net Loss Per Share Available to Common Stockholders - Calculation of Basic and Diluted Net Loss Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Numerator:
Net loss	$ (9,660)	$ (8,306)
Denominator:
Weighted average number of shares, basic and diluted	35,745	33,112
Net loss per share available to common stockholders
Basic and diluted net loss per common share available to common stockholders	$ (0.27)	$ (0.25)