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Fair Value Measurements - Schedule of Fair Value of Warrants (Detail)
 9 Months Ended 12 Months Ended
Sep. 30, 2017
Dec. 31, 2016
October 2016 Warrants [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Expected volatility (in hundredths) 142.46% 95.03%
Risk-free interest rates (in hundredths) 1.77% 1.93%
Expected life (in years) 4 years 7 days 4 years 9 months 18 days
June 2016 Series C Warrants [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Expected volatility (in hundredths)   94.19%
Risk-free interest rates (in hundredths)   2.01%
Expected life (in years)   5 years 6 months
July 2015 Series A Warrants [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Expected volatility (in hundredths) 165.32% 95.51%
Risk-free interest rates (in hundredths) 1.59% 1.59%
Expected life (in years) 2 years 9 months 22 days 3 years 7 months 6 days
February 2015 Warrants [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Expected volatility (in hundredths) 181.24% 95.52%
Risk-free interest rates (in hundredths) 1.53% 1.47%
Expected life (in years) 2 years 4 months 17 days 3 years 1 month 6 days
October 2013 Warrants [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Expected volatility (in hundredths) 227.68% 152.70%
Risk-free interest rates (in hundredths) 1.33% 1.20%
Expected life (in years) 1 year 29 days 1 year 9 months 18 days