Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2020	May 29, 2020
Document And Entity Information
Entity Registrant Name	REPLIMUNE GROUP, INC.
Entity Central Index Key	0001737953
Document Type	10-K
Document Period End Date	Mar. 31, 2020
Amendment Flag	false
Current Fiscal Year End Date	--03-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Public Float	$ 178.0
Entity Small Business	true
Entity Shell Company	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Common Stock, Shares Outstanding		36,784,130
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY