Warrants - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2009	Dec. 31, 2013
Class of Warrant or Right [Line Items]
Warrants to purchase an aggregate of shares of common stock					8,206,520
Warrant term					5 years
Estimated fair value of warrant					$ 22,900,000
Warrants outstanding	8,235,076		8,235,076			10,539,767
Change in fair value of warrants	$ 5,847,000	$ (7,407,000)	$ 11,529,000	$ 2,979,000
Liability
Class of Warrant or Right [Line Items]
Warrants to purchase an aggregate of shares of common stock			184,367
Exercise price of Warrants decreased						$ 3.93
Warrants outstanding	8,235,076		8,235,076			8,235,076
J. P. Morgan Securities LLC
Class of Warrant or Right [Line Items]
Warrants issued					464,520
Exercise price of Warrants decreased					$ 4.02
Warrant exercisable Period					6 months
Warrants
Class of Warrant or Right [Line Items]
Expected volatility					105.00%
Risk-free interest rate					2.14%
Expected life in years					5 years
Expected dividend yield					0.00%
Registered direct offering
Class of Warrant or Right [Line Items]
Sale of stock price per share						$ 3.50