Summary of Significant Accounting Policies - Basic and Diluted Net Loss Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Numerator
Net loss for basic EPS	$ (20,932)	$ (21,055)
Common stock warrants	(8,269)	0
Non-employee stock options and restricted stock units	(132)	0
Dilutive Securities	(8,401)	0
Net loss for diluted EPS	$ (29,333)	$ (21,055)
Denominator
Weighted average common shares outstanding, basic	139,309	100,809
Common stock warrants, shares	5,870	0
Non-employee stock options and restricted stock units, shares	144	0
Dilutive potential shares of common stock, shares	6,014	0
Weighted average common shares outstanding, diluted	145,323	100,809
Basic net loss per share, usd per share	$ (0.15)	$ (0.21)
Diluted net loss per share, usd per share	$ (0.20)	$ (0.21)