Net Loss Per Share - Computation of Common Shares Upon Exercise of Warrants and Basic and Diluted Net Loss Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Numerator
Net loss	$ (6,110)	$ (13,802)	$ (18,498)	$ (21,698)
Deemed dividend on convertible notes			(1,378)	(1,253)
Net loss attributable to common stockholders	(6,110)	(13,802)	(19,876)	(22,951)
Effect of potentially dilutive securities
Convertible notes	(1,089)		(118)
Warrants to purchase common stock	(201)		(201)
Net loss for diluted earnings per share	$ (7,400)	$ (13,802)	$ (20,195)	$ (22,951)
Denominator
Shares used for basic net loss per share	12,888	1,262	5,187	1,253
Effect of potentially dilutive securities
Convertible notes	1,043		20
Warrants to purchase common stock	86		22
Weighted average shares outstanding for diluted earnings per share	14,017	1,262	5,229	1,253
Basic net loss per share	$ (0.47)	$ (10.94)	$ (3.83)	$ (18.32)
Diluted net loss per share	$ (0.53)	$ (10.94)	$ (3.86)	$ (18.32)