Document and Entity Information - shares
9 Months Ended
Dec. 31, 2018
Feb. 12, 2019
Document And Entity Information    
Entity Registrant Name Replimune Group, Inc.  
Entity Central Index Key 0001737953  
Document Type 10-Q  
Document Period End Date Dec. 31, 2018  
Amendment Flag false  
Current Fiscal Year End Date --03-31  
Entity Current Reporting Status Yes  
Entity Filer Category Non-accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company true  
Entity Ex Transition Period true  
Entity Common Stock, Shares Outstanding   31,646,800
Document Fiscal Year Focus 2018  
Document Fiscal Period Focus Q3