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Warrant Liability - Summary of Changes in Fair Value of Warrant Liability (Detail) (USD $)
 6 Months Ended
Jun. 30, 2013
Class of Warrant or Right [Line Items]  
Number of warrants, ending balance 9,601,378
Series A Warrants [Member]
  
Class of Warrant or Right [Line Items]  
Number of warrants, beginning balance 8,166,895
Number of warrants exercised   
Number of warrants, ending balance 8,166,895
Fair value of warrant liability, beginning balance $ 8,952,059
Fair value of warrants exercised   
Fair value, changes in fair value at period end (716,808)
Fair value of warrant liability, ending balance $ 8,235,251