v3.5.0.2
Document and Entity Information - shares
9 Months Ended
Sep. 30, 2016
Oct. 21, 2016
Document Document And Entity Information [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Sep. 30, 2016  
Document Fiscal Year Focus 2016  
Document Fiscal Period Focus Q3  
Trading Symbol PRTA  
Entity Registrant Name Prothena Corp plc  
Entity Central Index Key 0001559053  
Current Fiscal Year End Date --12-31  
Entity Filer Category Large Accelerated Filer  
Entity Ordinary Shares Outstanding   34,488,428