| Cover Page - USD ($) | 12 Months Ended | | |
| Dec. 31, 2021 | Apr. 22, 2022 | Jun. 30, 2021 |
| Cover [Abstract] | | | |
| Document Type | 10-K/A | | |
| 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 | | 151,809,416 | |
| Amendment Flag | true | | |
| Document Fiscal Year Focus | 2021 | | |
| Document Fiscal Period Focus | FY | | |
| Entity Central Index Key | 0001453687 | | |
| Amendment Description | This Amendment No. 1 on Form 10-K/A, or the Form 10-K/A, is being filed by Selecta Biosciences, Inc., or Selecta, in order to disclose information required by Items 10, 11, 12, 13 and 14 of Part III of Form 10-K, which information was omitted from Selecta’s Form 10-K for the fiscal year ended December 31, 2021, or the Original Form 10-K, in reliance on Instruction G to Form 10-K. The Original Form 10-K was filed with the Securities and Exchange Commission, or SEC, on March 10, 2022. | | |
