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		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Numerator:
Net loss	$ (6,791)	$ (9,097)	$ (15,096)	$ (19,598)
Denominator:
Weighted average number of shares, basic and diluted	33,771	32,237	33,563	19,871
Net loss per share available to common stockholders
Basic and diluted net loss per common share available to common stockholders	$ (0.20)	$ (0.28)	$ (0.45)	$ (0.99)