v3.8.0.1
Document and Entity Information - USD ($)
$ in Billions
12 Months Ended
Dec. 31, 2017
Feb. 09, 2018
Jun. 30, 2017
Document Document And Entity Information [Abstract]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Dec. 31, 2017    
Document Fiscal Year Focus 2017    
Document Fiscal Period Focus FY    
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   38,540,539  
Entity Well-known Seasoned Issuer Yes    
Entity Current Reporting Status Yes    
Entity Voluntary Filers No    
Entity Public Float     $ 2.1