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Summary of Significant Accounting Policies - Summary of Common Stock Equivalents Outstanding (Detail) - shares
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Total potentially dilutive shares 5,852,654 4,064,974
Options to Purchase Common Stock [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Total potentially dilutive shares 5,839,261 4,048,377
Unvested Restricted Common Stock [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Total potentially dilutive shares 13,393 16,597