Fair Value of Financial Instruments - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended			1 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Oct. 31, 2009 October 2009 Offering [Member]
Derivatives, Fair Value [Line Items]
Short term investments	$ 0		$ 0		$ 15,433,967
Common stock, shares authorized under plan, in shares	12,020,442		12,020,442		10,942,973	1,362,500
Warrants to purchase common stock, in shares						681,250
Change in fair value of stock warrants	$ (4,444,804)	$ (1,065,498)	$ (4,394,778)	$ 5,399,569