Cover Page - USD ($)
 12 Months Ended
Dec. 31, 2021
Mar. 04, 2022
Jun. 30, 2021
Cover [Abstract]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2021    
Current Fiscal Year End Date --12-31    
Document Transition Report false    
Entity File Number 001-37798    
Entity Registrant Name Selecta Biosciences, Inc    
Entity Incorporation, State or Country Code DE    
Entity Tax Identification Number 26-1622110    
Entity Address, Address Line One 65 Grove Street,    
Entity Address, City or Town Watertown,    
Entity Address, State or Province MA    
Entity Address, Postal Zip Code 02472    
City Area Code 617    
Local Phone Number 923-1400    
Title of 12(b) Security Common Stock, $0.0001 par value per share    
Trading Symbol SELB    
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 Smaller Reporting Company true    
Entity Emerging Growth Company false    
ICFR Auditor Attestation Flag false    
Entity Shell Company false    
Entity Public Float     $ 366,839,496
Entity Common Stock, Shares Outstanding   124,288,850  
Documents Incorporated by Reference Portions of the registrant’s definitive Proxy Statement relating to its 2022 Annual Meeting of Stockholders to be filed with the Securities and Exchange Commission are incorporated by reference into Part III of this Annual Report on Form 10-K.    
Amendment Flag false    
Document Fiscal Year Focus 2021    
Document Fiscal Period Focus FY    
Entity Central Index Key 0001453687