Quarterly report pursuant to Section 13 or 15(d)

Research and Development Agreements - Additional Information (Detail)

v3.20.2
Research and Development Agreements - Additional Information (Detail) - USD ($)
 1 Months Ended 3 Months Ended 9 Months Ended 107 Months Ended
Nov. 30, 2019
Jul. 31, 2019
Sep. 30, 2018
Sep. 30, 2020
Mar. 31, 2020
Sep. 30, 2019
Sep. 30, 2020
Sep. 30, 2019
Nov. 30, 2019
Dec. 31, 2019
Research And Development Collaboration Agreements [Line Items]                    
Common stock, shares issued       49,963,732     49,963,732     45,589,157
Common stock, par value       $ 0.001     $ 0.001     $ 0.001
Revenue from grant       $ 4,298,000   $ 3,618,000 $ 15,348,000 $ 16,073,000    
Grant                    
Research And Development Collaboration Agreements [Line Items]                    
Revenue from grant       0   $ 431,000 3,210,000 $ 1,262,000    
CPRIT Agreement | Cancer Prevention and Research Institute of Texas                    
Research And Development Collaboration Agreements [Line Items]                    
Product development grant awarded     $ 15,200,000              
CPRIT Agreement | Cancer Prevention and Research Institute of Texas | ETB MT-3724                    
Research And Development Collaboration Agreements [Line Items]                    
Aggregate proceeds received from award granted                 $ 10,600,000  
Revenue from grant             16,400,000      
Grants Receivable       3,500,000     3,500,000      
Grant Agreements | Grants Revenue Receivable                    
Research And Development Collaboration Agreements [Line Items]                    
Reimbursement amounts submitted in excess of amounts received are recorded as receivables       3,500,000     3,500,000     $ 7,100,000
Takeda Development Agreement                    
Research And Development Collaboration Agreements [Line Items]                    
Total transaction price             29,800,000      
Upfront payment         $ 30,000,000.0          
Development milestone payment that is achievable             10,000,000.0      
Expected co-share payments payable       10,200,000     10,200,000      
Deferred revenue       2,700,000     2,700,000     6,100,000
Takeda Development Agreement | Clinical Development and Regulatory Milestones                    
Research And Development Collaboration Agreements [Line Items]                    
Milestone payments receivable if option is exercised   $ 307,500,000                
Takeda Development Agreement | Sales Milestone                    
Research And Development Collaboration Agreements [Line Items]                    
Milestone payments receivable if option is exercised   $ 325,000,000.0                
Takeda Multi Target Agreement | Takeda                    
Research And Development Collaboration Agreements [Line Items]                    
Deferred revenue       2,800,000     2,800,000     3,100,000
Cumulative payments received             5,000,000.0      
Aggregate milestone payments upon exercise of option to license ETBS       30,000,000.0     30,000,000.0      
Additional preclinical, clinical development and commercialization milestone payment       397,000,000.0     397,000,000.0      
Takeda Multi Target Agreement | Takeda | Maximum                    
Research And Development Collaboration Agreements [Line Items]                    
Contractual contingency fees             10,000,000.0      
Commercial milestone payment             150,000,000.0      
Vertex Collaboration Agreement                    
Research And Development Collaboration Agreements [Line Items]                    
Milestone payments receivable if option is exercised $ 180,000,000                  
Upfront payment 38,000,000                  
Deferred revenue       $ 20,300,000     $ 20,300,000     $ 27,500,000
Upfront payment, cash 23,000,000                  
Upfront payment, equity method investments $ 15,000,000               $ 15,000,000  
Common stock, shares issued 1,666,666               1,666,666  
Common stock, par value $ 0.001               $ 0.001  
Vertex Collaboration Agreement | Common Stock                    
Research And Development Collaboration Agreements [Line Items]                    
Purchase price per share $ 9.00               $ 9.00  
Fair value of allocated consideration $ 4,500,000                  
Vertex Collaboration Agreement | ETBs                    
Research And Development Collaboration Agreements [Line Items]                    
Aggregate milestone payments upon exercise of option to license ETBS 22,000,000               $ 22,000,000  
Vertex Collaboration Agreement | Sales Milestone                    
Research And Development Collaboration Agreements [Line Items]                    
Milestone payments receivable if option is exercised $ 70,000,000