Annual report pursuant to Section 13 and 15(d)

Research and Development Agreements - Additional Information (Detail)

v3.8.0.1
Research and Development Agreements - Additional Information (Detail) - USD ($)
 1 Months Ended 3 Months Ended 12 Months Ended 74 Months Ended
Nov. 30, 2011
Sep. 30, 2017
Mar. 31, 2017
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2017
Oct. 31, 2016
Research And Development Collaboration Agreements [Line Items]              
Collaboration revenue       $ 2,408,000 $ 0    
Grant revenue       987,000 1,880,000    
Other Collaboration Agreements | ETBs              
Research And Development Collaboration Agreements [Line Items]              
Collaboration revenue     $ 500,000        
Collaboration revenue receivable       250,000   $ 250,000  
Takeda Pharmaceuticals Inc | Takeda Collaboration Agreement              
Research And Development Collaboration Agreements [Line Items]              
Upfront payment for technology access fees and cost reimbursement             $ 2,000,000
Collaboration revenue       1,900,000      
Takeda Pharmaceuticals Inc | Takeda Multi Target Agreement              
Research And Development Collaboration Agreements [Line Items]              
Collaboration revenue       0      
Upfront technology access fee       1,000,000      
Additional fee received upon designation of each of two targets       2,000,000   2,000,000  
Aggregate milestones receivable upon exercise of option to license ETBS       25,000,000   25,000,000  
Clinical development and commercialization milestone entitled to potentially receive       547,000,000   547,000,000  
Aggregate purchase price   $ 20,000,000          
Cancer Prevention and Research Institute of Texas | Grant Agreements | ETB MT-3724              
Research And Development Collaboration Agreements [Line Items]              
Product development grant awarded $ 10,600,000            
Cancer Prevention and Research Institute of Texas | Grant Agreements | Product Development Grant | ETB MT-3724              
Research And Development Collaboration Agreements [Line Items]              
Grant revenue       $ 1,000,000 $ 1,900,000 $ 9,500,000