| Cover | May 19, 2021 |
| Cover [Abstract] | |
| Document Period End Date | May 19, 2021 |
| Entity Registrant Name | bluebird bio, Inc. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-35966 |
| Entity Tax Identification Number | 13-3680878 |
| Entity Address, Address Line One | 60 Binney Street |
| Entity Address, City or Town | Cambridge |
| Entity Address, State or Province | MA |
| Entity Address, Postal Zip Code | 02142 |
| City Area Code | 339 |
| Local Phone Number | 499-9300 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $0.01 par value per share |
| Trading Symbol | BLUE |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001293971 |
| Amendment Flag | false |
| Document Type | 8-K |
