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Net Loss Per Share - Additional Information (Detail) - shares
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Stock Option [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Common stock excluded from the calculation of weighted average shares for diluted net loss per share 6,774,000 4,705,000
Warrants [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Common stock excluded from the calculation of weighted average shares for diluted net loss per share 22,216,000 9,626,000