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		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Numerator
Net loss for basic EPS	$ (12,825)	$ (10,852)	$ 29,108	$ (45,240)
Common stock warrants	0	0	26,418	0
Net loss for diluted EPS	$ (12,825)	$ (10,852)	$ 2,690	$ (45,240)
Denominator
Weighted average common shares outstanding, basic	141,045	104,682	140,110	102,136
Common stock warrants, shares	0	0	364	0
Weighted average common shares outstanding, diluted	141,045	104,682	140,474	102,136
Basic net loss per share, usd per share	$ (0.09)	$ (0.10)	$ 0.21	$ (0.44)
Diluted net loss per share, usd per share	$ (0.09)	$ (0.10)	$ 0.02	$ (0.44)