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Warrant Liability - Summary of Changes in Fair Value of Warrant Liability (Detail) - USD ($)
 3 Months Ended 9 Months Ended
Sep. 30, 2015
Sep. 30, 2014
Sep. 30, 2015
Sep. 30, 2014
Class of Warrant or Right [Line Items]        
Fair value of warrant liability, beginning balance     $ 1,684,551  
Change in fair value of warrant liability $ 427,589 $ 4,076,360 1,068,626 $ 95,266
Fair value of warrant liability, ending balance $ 615,925   $ 615,925  
Series A Warrants [Member]        
Class of Warrant or Right [Line Items]        
Number of Warrants, beginning balance     6,936,880  
Number of Warrants, changes in fair value 0   0  
Number of Warrants, ending balance 6,936,880   6,936,880  
Fair value of warrant liability, beginning balance     $ 1,684,551  
Change in fair value of warrant liability     (1,068,626)  
Fair value of warrant liability, ending balance $ 615,925   $ 615,925