Fair Value of Financial Instruments - Warrant Liability Measured at Fair Value on a Recurring Basis (Detail) (Recurring [Member], Warrants [Member], USD $)	Sep. 30, 2013	Dec. 31, 2012
Derivative instruments:
Warrant liability	$ 3,514,622	$ 1,299,570
Level 1 [Member]
Derivative instruments:
Warrant liability
Level 2 [Member]
Derivative instruments:
Warrant liability
Level 3 [Member]
Derivative instruments:
Warrant liability	$ 3,514,622	$ 1,299,570