Quarterly report pursuant to Section 13 or 15(d)

Document and Entity Information

Document and Entity Information - shares
6 Months Ended
Jun. 30, 2019
Jul. 29, 2019
Document and Entity Information [Abstract]    
Entity Central Index Key 0001621227  
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Jun. 30, 2019  
Document Transition Report false  
Entity File Number 001-37368  
Entity Incorporation, State or Country Code X0  
Entity Address, Address Line One 60 Jubilee Avenue, Milton Park  
Entity Address, City or Town Abingdon, Oxfordshire  
Entity Address, Country GB  
Entity Address, Postal Zip Code OX14 4RX  
City Area Code 44  
Local Phone Number 1235 430000  
Entity Interactive Data Current Yes  
Entity Filer Category Large Accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Shell Company false  
Title of 12(b) Security American Depositary Shares, each representing 6 Ordinary Shares, par value £0.001 per share  
Trading Symbol ADAP  
Security Exchange Name NASDAQ  
Amendment Flag false  
Current Fiscal Year End Date --12-31  
Entity Current Reporting Status Yes  
Entity Common Stock, Shares Outstanding   630,762,860
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q2