Quarterly report pursuant to Section 13 or 15(d)

Commitments and Contingencies - Additional Information (Detail)

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Commitments and Contingencies - Additional Information (Detail)
 3 Months Ended
Feb. 15, 2018
USD ($)
Mar. 31, 2018
USD ($)
Mar. 31, 2017
USD ($)
Dec. 31, 2017
USD ($)
Feb. 28, 2017
ft²
Loss Contingencies [Line Items]          
Accrued termination charges   $ 0   $ 0  
Letter of credit issued   1,400,000   1,400,000  
Rental expenses   400,000 $ 300,000    
Letter of credit issued, classified as long-term restricted cash   1,200,000   1,200,000  
Ground lease expense   88,000 $ 37,000    
Liabilities related to indemnification agreements   0   $ 0  
Building          
Loss Contingencies [Line Items]          
Construction in progress   10,300,000      
Additional construction in progress   35,400,000      
Capitalized interest costs during the construction period   300,000      
Letter of Credit          
Loss Contingencies [Line Items]          
Letter of credit issued, classified as long-term restricted cash   $ 1,200,000      
Minimum          
Loss Contingencies [Line Items]          
Lease agreement term   2 years      
Maximum          
Loss Contingencies [Line Items]          
Lease agreement term   3 years      
South San Francisco California Lease          
Loss Contingencies [Line Items]          
Lease expiration date   Apr. 30, 2021      
Letter of credit renewal term   12 months      
South San Francisco California Lease | Letter of Credit          
Loss Contingencies [Line Items]          
Letter of credit issued   $ 200,000      
Westlake Village California Lease          
Loss Contingencies [Line Items]          
Lease expiration date   Apr. 30, 2019      
Thousand Oaks California Lease          
Loss Contingencies [Line Items]          
Lease agreement area of office, lab and cellular therapy manufacturing space | ft²         90,580
Build To Suit Lease Arrangement          
Loss Contingencies [Line Items]          
Lease initial term 15 years        
Lease commencement date   Feb. 15, 2018      
Contractual obligations $ 16,400,000        
Lease extension term, option one 10 years        
Lease extension term, option two 9 years