Document and Entity Information - shares
 9 Months Ended
Sep. 30, 2021
Oct. 29, 2021
Document and Entity Information    
Document Type 10-Q  
Document Quarterly Report true  
Document Transition Report false  
Document Period End Date Sep. 30, 2021  
Entity File Number 001-38586  
Entity Registrant Name RUBIUS THERAPEUTICS, INC.  
Entity Incorporation, State or Country Code DE  
Entity Tax Identification Number 46-2688109  
Entity Address, Address Line One 399 Binney Street  
Entity Address, Address Line Two Suite 300  
Entity Address, City or Town Cambridge  
Entity Address, State or Province MA  
Entity Address, Postal Zip Code 02139  
City Area Code 617  
Local Phone Number 679-9600  
Title of 12(b) Security Common Stock, par value $0.001 per share  
Trading Symbol RUBY  
Security Exchange Name NASDAQ  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Non-accelerated Filer  
Entity Small Business true  
Entity Emerging Growth Company true  
Entity Ex Transition Period false  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding   89,865,777
Current Fiscal Year End Date --12-31  
Document Fiscal Year Focus 2021  
Document Fiscal Period Focus Q3  
Entity Central Index Key 0001709401  
Amendment Flag false