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Warrants - Additional Information (Detail) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 6 Months Ended
Sep. 12, 2019
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2021
Jun. 30, 2020
Fair Value Assumptions Expected volatility Rate Maximum     73.90% 74.80% 73.74%
Fair Value Assumptions Risk Free Interest Rate Maximum     0.60% 1.15% 1.68%
Fair Value Assumptions Expected Term1   6 years 3 months      
Fair Value Assumptions Expected Dividend Rate   0.00% 0.00% 0.00% 0.00%
Net Proceeds from Underwriting         $ 13,015
Proceeds from private placement $ 52,500        
MD Anderson Warrant [Member]          
Number of securities into which the class of warrant converted   3,333,333   3,333,333  
Warrant exercise per share   $ 0.001   $ 0.001  
fair value of adjustment of warrants       $ 14,500  
Warrant Expiry date   Dec. 31, 2026   Dec. 31, 2026  
Securities Purchase Agreement [Member]          
Net Proceeds from Underwriting       $ 47,100  
Private Placement [Member]          
Number of securities into which the class of warrant converted 17,803,031 18,939,394   18,939,394  
Warrant exercise per share $ 3.01 $ 3.01   $ 3.01  
fair value of adjustment of warrants       $ 18,400  
Fair Value Assumptions Expected volatility Rate Maximum       71.00%  
Fair Value Assumptions Risk Free Interest Rate Maximum       2.99%  
Fair Value Assumptions Expected Term1       5 years  
Fair Value Assumptions Expected Dividend Rate       0.00%  
Placement agent fees and other expenses $ 1,100        
Private Placement [Member] | New Warrants [Member]          
Number of securities into which the class of warrant converted 17,803,031        
Warrant exercise per share $ 7.00        
Non-cash inducement warrant expense       $ 60,800