v3.19.2
Document and Entity Information - shares
6 Months Ended
Jun. 30, 2019
Jul. 19, 2019
Document Document And Entity Information [Abstract]    
Entity Current Reporting Status Yes  
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Jun. 30, 2019  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q2  
Entity Registrant Name Prothena Corp plc  
Entity Central Index Key 0001559053  
Current Fiscal Year End Date --12-31  
Entity Filer Category Accelerated Filer  
Entity Small Business true  
Entity Emerging Growth Company false  
Entity Shell Company false  
Entity Ordinary Shares Outstanding   39,896,561