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ORGANIZATION, BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIIES - Additional Information (Detail)
 12 Months Ended
Dec. 31, 2021
USD ($)
segment
$ / shares
shares
Dec. 31, 2020
USD ($)
$ / shares
shares
Dec. 31, 2019
USD ($)
$ / shares
shares
Organization and Summary of Significant Accounting Policies [Line Items]      
Revenues $ 110,701,000 $ 118,192,000 $ 102,428,000
Net loss $ (178,297,000) $ (121,122,000) $ (95,419,000)
Earnings per share, basic (in dollars per share) | $ / shares $ (1.23) $ (0.90) $ (0.85)
Goodwill and intangible asset impairment $ 0    
Impairment of long-lived assets held-for-use 0    
Letter of credit $ 1,500,000    
Stock options and RSUs outstanding (in shares) | shares 15,159,908 14,237,871 10,750,550
Number of operating segments | segment 1    
Pfizer SB-525      
Organization and Summary of Significant Accounting Policies [Line Items]      
Revenues $ 0    
Pfizer SB-525 | Change in collaboration agreement scope | Collaborative arrangement      
Organization and Summary of Significant Accounting Policies [Line Items]      
Revenues 1,600,000 $ 8,900,000 $ 5,700,000
Net loss $ 1,600,000 $ 8,900,000 $ 5,700,000
Earnings per share, basic (in dollars per share) | $ / shares $ 0.01 $ 0.06 $ 0.05
Minimum      
Organization and Summary of Significant Accounting Policies [Line Items]      
Estimated useful lives of related assets 3 years    
Maximum      
Organization and Summary of Significant Accounting Policies [Line Items]      
Estimated useful lives of related assets 5 years