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Warrants (Fair Value of Warrants is Estimated Using Black-Scholes Option Pricing Model) (Detail) - $ / shares
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
March 2015 Warrants [Member]    
Class of Warrant or Right [Line Items]    
Strike price $ 2.08  
Expected term (years) 4 years 2 months 19 days  
Volatility % 75.85%  
Risk-free rate % 1.58%  
September 2013 Warrant [Member]    
Class of Warrant or Right [Line Items]    
Strike price $ 2.50 $ 2.50
Expected term (years) 2 years 8 months 19 days 3 years 8 months 19 days
Volatility % 74.70% 75.60%
Risk-free rate % 1.24% 1.30%
December 2012 Warrants [Member]    
Class of Warrant or Right [Line Items]    
Strike price $ 1.83 $ 1.90
Expected term (years) 1 year 11 months 23 days 2 years 11 months 23 days
Volatility % 76.37% 76.85%
Risk-free rate % 1.05% 1.09%
April 2011 Warrants [Member]    
Class of Warrant or Right [Line Items]    
Strike price $ 0.65 $ 0.65
Expected term (years) 1 year 3 months 22 days 2 years 3 months 22 days
Volatility % 65.60% 78.24%
Risk-free rate % 0.77% 0.80%
March 2011 Warrants [Member]    
Class of Warrant or Right [Line Items]    
Strike price $ 0.65 $ 0.65
Expected term (years) 2 months 5 days 1 year 2 months 5 days
Volatility % 47.98% 77.38%
Risk-free rate % 0.00% 0.32%
March 2010 Warrants [Member]    
Class of Warrant or Right [Line Items]    
Strike price $ 2.02 $ 2.15
Expected term (years) 2 months 27 days 1 year 2 months 27 days
Volatility % 71.41% 77.12%
Risk-free rate % 0.00% 0.35%