Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Feb. 10, 2017	Jun. 30, 2016
Document Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2016
Document Fiscal Year Focus	2016
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		35,028,721
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Public Float			$ 1,200.9