Commitments and Contingencies - Additional Information (Detail)
 1 Months Ended 3 Months Ended 12 Months Ended
Jan. 31, 2019
USD ($)
RenewalTerm
Sep. 30, 2018
Mar. 31, 2017
USD ($)
ft²
Feb. 29, 2016
Mar. 31, 2021
Dec. 31, 2021
USD ($)
RenewalTerm
Dec. 31, 2020
USD ($)
Dec. 31, 2019
USD ($)
Sep. 30, 2021
May 31, 2019
USD ($)
Sep. 30, 2017
USD ($)
Feb. 28, 2016
USD ($)
Commitments and Contingencies Disclosure [Line Items]                        
Operating lease cash security deposit           $ 1,305,000 $ 1,218,000          
Operating lease right-of-use assets           22,920,000 21,344,000          
Lease liability           26,419,000            
Research and Development Expense           97,490,000 88,643,000 $ 82,896,000        
Contract Research Organization [Member]                        
Commitments and Contingencies Disclosure [Line Items]                        
Maximum milestone payments                   $ 34,800,000 $ 36,400,000  
Research and Development Expense           0 0 $ 1,000,000.0        
Emeryville California [Member]                        
Commitments and Contingencies Disclosure [Line Items]                        
Operating leasing term 120 months                      
Operating lease cash security deposit           600,000 600,000          
Operating leasing renewal option to extend lease 5 years                      
Operating leases number of renewal terms | RenewalTerm 2                      
Tenant improvement allowance $ 4,000,000.0                      
Operating lease right-of-use assets           8,700,000 9,300,000          
Lease liability           13,900,000 14,800,000          
Pleasanton [Member]                        
Commitments and Contingencies Disclosure [Line Items]                        
Operating leasing term                   64 months    
Operating leasing renewal option to extend lease     5 years                  
Tenant improvement allowance     $ 1,200,000             $ 100,000    
Operating lease right-of-use assets           200,000 300,000          
Lease liability           300,000 400,000          
Net rentable area | ft²     42,620                  
Lease expiration date     Nov. 30, 2024                  
Letters of credit outstanding, amount     $ 1,000,000.0                  
Withdrawal from irrevocable letters of credit           0            
Cambridge Massachusetts [Member]                        
Commitments and Contingencies Disclosure [Line Items]                        
Operating leasing term   24 months     17 months             67 months
Operating lease cash security deposit           $ 700,000 $ 600,000          
Tenant improvement allowance                       $ 2,100,000
Operating lease termination date   2023-01   2025-04                
Storage space commenced         Apr. 01, 2021              
Boston Lease [Member]                        
Commitments and Contingencies Disclosure [Line Items]                        
Operating leasing term                 120 months      
Operating leasing renewal option to extend lease           5 years            
Operating leases number of renewal terms | RenewalTerm           2            
Tenant improvement allowance           $ 19,100,000            
Lease liability           79,100,000            
Letters of credit outstanding, amount           4,600,000            
Withdrawal from irrevocable letters of credit           $ 0            
Operations expected commenced date           2022-11            
Restricted cash deposit used as collateral for letter of credit           $ 4,700,000            
Lease expiration term           2033-01