Quarterly report pursuant to Section 13 or 15(d)

Leases - Additional Information (Detail)

v3.19.1
Leases - Additional Information (Detail)
$ in Millions
3 Months Ended 12 Months Ended
Feb. 15, 2017
USD ($)
ft²
Mar. 31, 2019
USD ($)
Mar. 31, 2018
USD ($)
Dec. 31, 2018
USD ($)
Lessee Lease Description [Line Items]        
Rent expenses under operating leases     $ 0.4  
South San Francisco California Lease        
Lessee Lease Description [Line Items]        
Lease expiration date   Apr. 30, 2021    
Letter of credit renewal term   12 months    
South San Francisco California Lease | Letter of Credit        
Lessee Lease Description [Line Items]        
Letter of credit maintained   $ 0.2    
Thousand Oaks California lease        
Lessee Lease Description [Line Items]        
Lease expiration date   Feb. 28, 2026    
Lease agreement area of office, lab and cellular therapy manufacturing space | ft² 90,580      
Lease commencement date Feb. 15, 2018      
Lease initial term 15 years      
Contractual obligations $ 16.4      
Lease extension term, option one 10 years      
Lease extension term, option two 9 years      
Thousand Oaks California lease | Letter of Credit        
Lessee Lease Description [Line Items]        
Letter of credit issued, classified as long-term restricted cash $ 1.2      
Build To Suit Lease Arrangement | Building        
Lessee Lease Description [Line Items]        
Construction in progress       $ 10.3
Capitalized interest costs during the construction period       $ 0.3