v3.26.1
Cover - USD ($)
$ in Millions
 12 Months Ended
Mar. 31, 2026
Jun. 25, 2026
Sep. 30, 2025
Cover [Abstract]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Mar. 31, 2026    
Current Fiscal Year End Date --03-31    
Document Transition Report false    
Entity File Number 001-38596    
Entity Registrant Name REPLIMUNE GROUP, INC.    
Entity Incorporation, State or Country Code DE    
Entity Tax Identification Number 82-2082553    
Entity Address, Address Line One 500 Unicorn Park Drive    
Entity Address, Address Line Two Suite 303    
Entity Address, City or Town Woburn    
Entity Address, State or Province MA    
Entity Address, Postal Zip Code 01801    
City Area Code 781    
Local Phone Number 222-9600    
Title of 12(b) Security Common Stock, par value $0.001 per share    
Trading Symbol REPL    
Security Exchange Name NASDAQ    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Non-accelerated Filer    
Entity Small Business true    
Entity Emerging Growth Company false    
Auditor Attestation Flag false    
Document Financial Statement Error Correction [Flag] false    
Entity Shell Company false    
Entity Public Float     $ 234.5
Entity Common Stock, Shares Outstanding   83,945,161  
Documents Incorporated by Reference
The registrant intends to file a definitive proxy statement pursuant to Regulation 14A within 120 days of the end of the fiscal year ended March 31, 2026. Portions of such definitive proxy statement are incorporated by reference into Part III of this Annual Report on Form 10-K.
    
Entity Central Index Key 0001737953    
Amendment Flag false    
Document Fiscal Year Focus 2026    
Document Fiscal Period Focus FY