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Warrant Liability (Details) (USD $)
 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Assumptions used for the Black-Scholes option pricing model      
Expected life (years) 6 years 4 months 24 days 7 years 4 months 24 days 7 years 2 months 12 days
Fair value of warrant liability $ 9,265,365 $ 6,042,315  
Change in fair value of warrant liability (5,944,571) 6,612,092 3,005,040
Warrant agreement 2008 [Member]
      
Assumptions used for the Black-Scholes option pricing model      
Expected life (years) 1 year 4 months 24 days 2 years 4 months 24 days  
Risk-free interest rate 0.20% 0.30%  
Expected volatility 108.20% 74.10%  
Expected dividend yield 0.00% 0.00%  
Fair value of warrant liability 44,628 2,224  
Change in fair value of warrant liability $ 42,404