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Warrants (Fair Value of Warrants is Estimated Using Black-Scholes Option Pricing Model) (Detail) - $ / shares
 6 Months Ended 12 Months Ended
Jun. 30, 2016
Dec. 31, 2014
Dec. 31, 2015
January 2016 Warrants [Member]      
Class of Warrant or Right [Line Items]      
Strike price $ 1.42    
Expected term (years) 4 years 6 months 7 days    
Volatility % 113.70%    
Risk-free rate % 0.94%    
March 2015 Warrants [Member]      
Class of Warrant or Right [Line Items]      
Strike price $ 2.08   $ 2.08
Expected term (years) 3 years 8 months 19 days 4 years 2 months 19 days  
Volatility % 122.36%   75.85%
Risk-free rate % 0.82%   1.58%
September 2013 Warrant [Member]      
Class of Warrant or Right [Line Items]      
Strike price $ 2.50   $ 2.50
Expected term (years) 2 years 2 months 19 days 2 years 8 months 19 days  
Volatility % 139.26%   74.70%
Risk-free rate % 0.61%   1.24%
December 2012 Warrants [Member]      
Class of Warrant or Right [Line Items]      
Strike price $ 1.75   $ 1.83
Expected term (years) 1 year 5 months 23 days 1 year 11 months 23 days  
Volatility % 167.41%   76.37%
Risk-free rate % 0.51%   1.05%
April 2011 Warrants [Member]      
Class of Warrant or Right [Line Items]      
Strike price $ 0.65   $ 0.65
Expected term (years) 9 months 22 days 1 year 3 months 22 days  
Volatility % 218.93%   65.60%
Risk-free rate % 0.42%   0.77%
March 2011 Warrants [Member]      
Class of Warrant or Right [Line Items]      
Strike price     $ 0.65
Expected term (years)   2 months 5 days  
Volatility %     47.98%
Risk-free rate %     0.00%
March 2010 Warrants [Member]      
Class of Warrant or Right [Line Items]      
Strike price $ 1.92   $ 2.02
Expected term (years) 3 months 1 year  
Volatility % 218.93%   71.41%
Risk-free rate % 0.19%   0.00%