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Warrant Liability - Summary of Changes in Fair Value of Warrant Liability (Detail) (USD $)
 12 Months Ended
Dec. 31, 2013
Class of Warrant or Right [Line Items]  
Number of Warrants, ending balance 9,551,378
Series A Warrants [Member]
  
Class of Warrant or Right [Line Items]  
Number of Warrants, beginning balance 8,501,429
Number of Warrants, Less exercised (384,534)
Number of Warrants, ending balance 8,116,895
Fair value of warrant liability, beginning balance $ 9,157,397
Fair value of warrants exercised (470,303)
Fair value, changes in fair value at period end (3,145,285)
Fair value of warrant liability, ending balance $ 5,541,809