| Document and Entity Information | Apr. 29, 2021 |
| Cover [Abstract] | |
| Entity Registrant Name | SELECTA BIOSCIENCES INC |
| Amendment Flag | false |
| Entity Central Index Key | 0001453687 |
| Document Type | 8-K |
| Document Period End Date | Apr. 29, 2021 |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-37798 |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock (Par Value $0.0001) |
| Trading Symbol | SELB |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | true |
