Document and Entity Information - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2020
Jan. 29, 2021
Jun. 30, 2020
Document and Entity Information      
Document Type 10-K    
Document Annual Report true    
Document Transition Report false    
Document Period End Date Dec. 31, 2020    
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 Accelerated Filer    
Entity Small Business true    
Entity Emerging Growth Company true    
Entity Ex Transition Period false    
Entity Shell Company false    
ICFR Auditor Attestation Flag true    
Entity Common Stock, Shares Outstanding   81,181,972  
Current Fiscal Year End Date --12-31    
Document Fiscal Year Focus 2020    
Document Fiscal Period Focus FY    
Entity Central Index Key 0001709401    
Amendment Flag false    
Entity Well-known Seasoned Issuer No    
Entity Public Float     $ 222.3
Entity Voluntary Filers No