Fair Value of Assets and Liabilities - Assets and Liabilities Measured at Fair Value Recurring Basis (Detail) (USD $)	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2011
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative warrant liability	$ 0	$ 14,584,818	$ 23,527,882	$ 35,473,230
Level 1 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative warrant liability
Level 2 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative warrant liability		14,584,818
Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative warrant liability