Warrants - Additional Information (Detail) (USD $)	12 Months Ended				1 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2009	Oct. 31, 2009
Class of Warrant or Right [Line Items]
Warrants to purchase an aggregate of shares of common stock	184,367			8,206,520
Warrant term				5 years
Estimated fair value of warrant				$ 22,900,000
Warrants outstanding	8,235,076
Other income (expense)	(5,000)	(579,000)	(13,000)
Warrants exercised	4,004,907	135,346	553,914
Conversion of Warrants to Common Stock	3,725,277	112,808	259,660
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%
Liability
Class of Warrant or Right [Line Items]
Warrants outstanding	1,755,845	0	373,617
Classified warrants		11,800,000	13,000,000
Warrants expired	6,479,231		579
Equity
Class of Warrant or Right [Line Items]
Warrants outstanding	2,249,062	135,346	186,297
Warrants expired	12,329	706,708	1,359,317
Liability Warrants
Class of Warrant or Right [Line Items]
Other income (expense)		(1,200,000)	(6,100,000)
Registered direct offering
Class of Warrant or Right [Line Items]
Sale of stock price per share		$ 3.50
Private Placement
Class of Warrant or Right [Line Items]
Warrants to purchase an aggregate of shares of common stock				2,910,954
Warrant exercise price				$ 2.04
Warrant exercisable Period				5 years
Estimated fair value of warrant				$ 4,200,000
Warrants exercised					136,986
Private Placement | Warrants
Class of Warrant or Right [Line Items]
Expected volatility				105.00%
Risk-free interest rate				2.41%
Expected life in years				5 years
Expected dividend yield				0.00%
J. P. Morgan Securities LLC
Class of Warrant or Right [Line Items]
Warrants issued				464,520
Warrant exercise price				$ 4.02
Warrant exercisable Period				6 months
Placement Agents | Private Placement
Class of Warrant or Right [Line Items]
Warrants to purchase an aggregate of shares of common stock				138,617