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Warrants (Fair Value of Warrants is Estimated Using Black-Scholes Option Pricing Model) (Detail) (USD $)
 3 Months Ended 9 Months Ended
Sep. 30, 2013
Sep. 30, 2014
Dec. 31, 2013
December 2012 Warrants [Member]
      
Class of Warrant or Right [Line Items]      
Strike price   $ 1.90 $ 1.90
Expected term (years) 3 years 11 months 23 days 3 years 2 months 23 days  
Volatility %   76.97% 71.38%
Risk-free rate %   1.15% 1.25%
April 2011 Warrants [Member]
      
Class of Warrant or Right [Line Items]      
Strike price   $ 0.65 $ 0.65
Expected term (years) 3 years 3 months 22 days 2 years 6 months 22 days  
Volatility %   78.24% 71.71%
Risk-free rate %   0.85% 0.93%
March 2011 Warrants [Member]
      
Class of Warrant or Right [Line Items]      
Strike price   $ 0.65 $ 0.65
Expected term (years) 2 years 2 months 5 days 1 year 5 months 5 days  
Volatility %   79.41% 73.45%
Risk-free rate %   0.32% 0.45%
March 2010 Warrants [Member]
      
Class of Warrant or Right [Line Items]      
Strike price   $ 2.15 $ 2.15
Expected term (years) 2 years 2 months 27 days 1 year 5 months 27 days  
Volatility %   79.03% 73.36%
Risk-free rate %   0.35% 0.47%
August 2009 Warrants [Member]
      
Class of Warrant or Right [Line Items]      
Strike price     $ 4.50
Expected term (years) 7 months 2 days    
Volatility %     66.85%
Risk-free rate %     0.11%
September 2013 Warrant [Member]
      
Class of Warrant or Right [Line Items]      
Strike price   $ 2.50 $ 2.50
Expected term (years) 4 years 8 months 19 days 3 years 11 months 19 days  
Volatility %   74.39% 71.97%
Risk-free rate %   1.41% 1.61%