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Warrants - Summary of Fair Value Used to Determine Warrants' Initial Carrying Value (Detail) - Common Stock Warrants [Member]
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]        
Expected volatility 87.00% 71.00% 87.00% 75.00%
Expected term (years) 5 years 4 years 2 months 19 days 5 years 4 years 6 months 14 days
Risk-free interest rate 1.76% 1.08% 1.76% 1.29%
Expected dividend yield 0.00% 0.00% 0.00% 0.00%