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Summary of Significant Accounting Policies - Derivative Instruments Measured at Fair Value (Detail) (Warrant [Member], USD $)
Jun. 30, 2013
Dec. 31, 2012
Fair Value Inputs Level 1 [Member]
   
Derivatives, Fair Value [Line Items]    
Derivative instruments measured at fair value      
Fair Value Inputs Level 2 [Member]
   
Derivatives, Fair Value [Line Items]    
Derivative instruments measured at fair value (7,649,962) (4,969,752)
Fair Value Inputs Level 3 [Member]
   
Derivatives, Fair Value [Line Items]    
Derivative instruments measured at fair value