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Stock-Based Compensation - Summary of Stock Option Activity (Detail) - 2006 and 2014 Stock Option Plans and Inducement Plan [Member] - Stock Options [Member] - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Share-Based Compensation    
Number of Shares Outstanding, beginning of the period 6,353,330  
Number of Shares, Granted 4,306,750  
Number of Shares, Exercised (49,563) (2,119)
Number of Shares, Forfeited (1,232,700)  
Number of Shares, Canceled (781,888)  
Number of Shares Outstanding, end of the period 8,595,929 6,353,330
Number of Shares, Exercisable 4,098,314  
Number of Shares, Vested or expected to vest 7,650,363  
Weighted-Average Exercise Price Per Share Outstanding, beginning of the period $ 4.95  
Weighted-Average Exercise Price Per Share, Granted 1.02  
Weighted-Average Exercise Price Per Share, Exercised 0.61  
Weighted-Average Exercise Price Per Share, Forfeited 3.04  
Weighted-Average Exercise Price Per Share, Canceled 5.43  
Weighted-Average Exercise Price Per Share Outstanding, end of the period 3.24 $ 4.95
Weighted-Average Exercise Price Per Share, Exercisable 4.98  
Weighted-Average Exercise Price Per Share, Vested or expected to vest $ 3.46  
Weighted-Average Remaining Contractual Term, Outstanding 7 years 9 months 7 years 3 months 14 days
Weighted-Average Remaining Contractual Term, Exercisable 6 years 6 months 25 days  
Weighted-Average Remaining Contractual Term, Vested or expected to vest 7 years 7 months 9 days  
Aggregate Intrinsic Value, Outstanding, beginning of the period $ 229  
Aggregate Intrinsic Value, Exercised 33  
Aggregate Intrinsic Value Outstanding, end of the period 1,011 $ 229
Aggregate Intrinsic Value, Exercisable 272  
Aggregate Intrinsic Value, Vested or expected to vest $ 845