Warrants - Additional Information (Detail) (USD $)	1 Months Ended			3 Months Ended		9 Months Ended		12 Months Ended	121 Months Ended		12 Months Ended	1 Months Ended		12 Months Ended		12 Months Ended
	Feb. 23, 2007	May 03, 2006	May 31, 2005	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2009 Y	Sep. 30, 2013	Dec. 31, 2012	Dec. 31, 2009 J. P. Morgan Securities LLC	May 31, 2012 Private Placement	May 31, 2005 Private Placement	Dec. 31, 2009 Private Placement	Dec. 31, 2006 Private Placement	Dec. 31, 2009 Registered direct offering
Class of Warrant or Right [Line Items]
Warrant issued	1,359,317	706,708	579										419,786
Warrant exercised												419,207	11,083
Warrant outstanding				10,392,387		10,392,387			10,392,387	11,197,454			408,703
Value of warrant issued													$ 1,600,000
Sale of stock price per share													$ 4.75	$ 1.825	$ 4.63
Revised price for warrants													$ 4.69	$ 4.25		$ 3.93
Common stock warrants exercise price														$ 2.04
Issuable price for common stock																$ 3.10
Warrant expired												579
Warrants to purchase an aggregate of shares of common stock								8,206,520
Warrants issued											464,520
Warrant exercise Price											$ 4.02
Warrant exercisable Period											6 months
Warrant term								5 years
Estimated fair value of warrant								22,900,000
Expected volatility								105.00%
Risk free interest								2.14%
Expected life								5
Expected dividend yield								0.00%
Change in fair value of warrants				$ (7,407,000)	$ 3,945,000	$ 2,979,000	$ (2,516,000)		$ 13,750,000
Warrants expiration date	Feb. 23, 2012	May 03, 2013	May 31, 2012
Warrant exercise price per share	5.75	5.09	3.93