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Fair Value of Financial Assets and Liabilities - Derivative Instruments (Valuation Assumptions Used for Series B Convertible Stock) (Details) - $ / shares
12 Months Ended
Dec. 31, 2015
Sep. 30, 2016
Common stock closing price   $ 1.52
Series B redeemable convertible preferred stock [Member]    
Dividend yield 0.00%  
Exercise price $ 7.00  
Common stock closing price $ 3.98  
Series B redeemable convertible preferred stock [Member] | Minimum [Member]    
Volatility 108.00%  
Expected term (years) 6 months  
Risk-free interest rate 0.49%  
Series B redeemable convertible preferred stock [Member] | Maximum [Member]    
Volatility 117.00%  
Expected term (years) 2 years 6 months  
Risk-free interest rate 1.19%