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Preferred Stock, Common Stock and Stockholders' Equity - Summary of Common Stock Reserved for Future Issuance (Detail) - shares
Dec. 31, 2018
Apr. 26, 2018
Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]      
Stock options issued and outstanding 3,017,624   2,131,624
Authorized for future option grants 986,801   72,801
Warrants to purchase common stock 2,713,561   2,797,561
Authorized for employee stock purchase plan 163,065   91,934
Total common stock reserved for future issuance 6,881,051 6,286,425 5,093,920