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Net Loss Per Share Attributable to Common Stockholders - Potentially Dilutive Securities Excluded from Computation of Diluted Weighted-Average Shares Outstanding (Detail) - shares
3 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Options to Purchase Common Stock [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Antidilutive securities excluded from computation of diluted weighted-average shares outstanding 5,441,105 3,991,586
Warrants [Member] | Common Stock [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Antidilutive securities excluded from computation of diluted weighted-average shares outstanding 365,564 300,564