Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Additional Information (Detail)

v3.8.0.1
Summary of Significant Accounting Policies - Additional Information (Detail)
 12 Months Ended
Aug. 01, 2017
shares
Dec. 31, 2017
USD ($)
Segment
Dec. 31, 2016
USD ($)
Organization And Summary Of Significant Accounting Policies [Line Items]      
Reverse stock split of common stock, description   11-for-1 reverse stock split  
Reverse stock split of common stock conversion ratio 11    
Number of issued and outstanding shares of common stock converted into one issued and outstanding share of common stock 11    
Number of issued and outstanding shares of common stock converted by every eleven shares of issued and outstanding common stock 1    
Impairment of long lived assets | $   $ 0 $ 0
Reportable segment | Segment   1  
Leasehold Improvements | Minimum      
Organization And Summary Of Significant Accounting Policies [Line Items]      
Property and equipment, estimated useful lives   5 years  
Leasehold Improvements | Maximum      
Organization And Summary Of Significant Accounting Policies [Line Items]      
Property and equipment, estimated useful lives   7 years  
Takeda Pharmaceuticals Inc      
Organization And Summary Of Significant Accounting Policies [Line Items]      
Accounts receivable | $   $ 0 $ 0
Revenue | Credit Risk      
Organization And Summary Of Significant Accounting Policies [Line Items]      
Percentage of total revenues   56.00%  
Threshold      
Organization And Summary Of Significant Accounting Policies [Line Items]      
Reverse stock split of common stock, description 11-for-1 reverse stock split    
Reverse stock split of common stock conversion ratio 11    
Exchange ratio of company common stock shares exchanged for each share owned by private molecular stockholders 7.7844    
Threshold equity holders ownership interest 34.40%    
Private Molecular equity holders ownership interest 65.60%