Basis of Presentation - Reconciliation of Beginning and Ending Balances of Assets and Liabilities Measured at Fair Value Using Significant Observable Inputs (Detail) (USD $)	6 Months Ended
	Jun. 30, 2013
Assets [Member]
Basis Of Presentation [Line Items]
Warrant asset as of December 31, 2012	$ 50,300
Decrease in fair value of warrants	(50,300)
Warrant asset as of June 30, 2013
Warrant asset as of December 31, 2012	2,000,000
Decrease in fair value of warrants (Note 7)	(2,000,000)
Warrant asset as of June 30, 2013
Liabilities [Member]
Basis Of Presentation [Line Items]
Warrant liability as of December 31, 2012	4,497,977
Decrease in fair value of warrants	(1,467,837)
Warrant liability as of June 30, 2013	$ 3,030,140
Warrant liability as of December 31, 2012	2,009,436
Decrease in fair value of warrants
Warrant liability as of June 30, 2013	2,009,436