Quarterly report pursuant to Section 13 or 15(d)

Net Loss Per Share of Common Stock - Schedule of Antidilutive Securities Excluded from Computation of Diluted Weighted Average Shares Outstanding (Detail)

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Net Loss Per Share of Common Stock - Schedule of Antidilutive Securities Excluded from Computation of Diluted Weighted Average Shares Outstanding (Detail) - shares
9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Potentially antidilutive securities outstanding excluded from the computation of diluted weighted average shares 38,513,380 42,287,087
Employee Stock Options [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Potentially antidilutive securities outstanding excluded from the computation of diluted weighted average shares 7,248,198 6,016,984
Warrants [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Potentially antidilutive securities outstanding excluded from the computation of diluted weighted average shares 31,265,182 36,270,103