Description of the business	9 Months Ended
Description of the business	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of the business	Description of the business bluebird bio, Inc. (the “Company” or “bluebird”) was incorporated in Delaware on April 16, 1992, and is headquartered in Cambridge, Massachusetts. The Company is a biotechnology company committed to researching, developing and commercializing, following marketing approval, potentially transformative gene therapies for severe genetic disease. Since its inception, the Company has devoted substantially all of its resources to its research and development efforts relating to its product candidates, including activities to manufacture product candidates, conduct clinical studies of its product candidates, perform preclinical research to identify new product candidates and provide selling, general and administrative support for these operations, including commercial activities in Europe as well as commercial-readiness activities in the United States. In November 2021, the Company completed the separation of its severe genetic disease and oncology programs into two separate, independent publicly traded companies, bluebird bio, Inc. and 2seventy bio, Inc., a Delaware corporation and wholly-owned subsidiary of the Company prior to the separation. bluebird bio, Inc. intends to retain its severe genetic disease programs, with a focus on the U.S. market. The Company’s programs in severe genetic diseases include programs for transfusion-dependent β-thalassemia, or TDT, sickle cell disease, or SCD, and cerebral adrenoleukodystrophy, or CALD. The Company also expects to make focused investments in research and development efforts on optimizing our existing programs as well as on pipeline programs in severe genetic diseases. 2seventy bio, Inc. is expected to focus on the Company's former oncology programs, including the anti-BCMA CAR T programs for multiple myeloma under the Company’s collaboration arrangement with Bristol-Myers Squibb ("BMS"). Please refer to Note 10, Collaborative arrangements and strategic partnerships, for further discussion of the Company’s collaboration with BMS. The results for the period ended September 30, 2021 reflect the combined results of the Company and 2seventy bio prior to the effectiveness of the separation, and the forward-looking statements contained within pertain to the Company's severe genetic disease operations, unless otherwise noted. In accordance with Accounting Standards Codification (“ASC”) 205-40, Going Concern, the Company evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about its ability to continue as a going concern within one year after the date that the consolidated financial statements are issued. The Company has incurred losses since inception and to date has financed its operations primarily through the sale of equity securities and, to a lesser extent, through collaboration agreements and grants from governmental agencies and charitable foundations. As of September 30, 2021, the Company had an accumulated deficit of $3.56 billion. During the nine months ended September 30, 2021, the Company incurred a loss of $664.3 million and used $495.9 million of cash in operations. The Company expects to continue to generate operating losses and negative operating cash flows for the next few years and will need additional funding to support its planned operating activities through profitability. The transition to profitability is dependent upon the successful development, approval, and commercialization of beti-cel, eli-cel, and LentiGlobin for SCD, and the achievement of a level of revenues adequate to support its cost structure. As of September 30, 2021, the Company had cash, cash equivalents and marketable securities of $970.7 million. Upon separation, the Company funded 2seventy bio with approximately $441.5 million, which has reduced the amount of cash available to the Company as of the date of separation. The Company expects its cash, cash equivalents and marketable securities, subsequent to the amount funded to 2seventy bio, will be sufficient to fund current planned operations for at least the next twelve months from the date of issuance of these financial statements. The Company anticipates reduced 2022 spending, including projected savings through the move of the Company's headquarters to Assembly Row in Somerville, Massachusetts, and the orderly wind down of European operations. This, together with other anticipated cash inflows, which include both the potential sale of priority review vouchers that would be issued with anticipated U.S. regulatory approvals of BLAs for beti-cel and eli-cel, and the pursuit of additional cash resources through public or private equity or debt financings, are expected to further strengthen the Company's financial condition. Management's expectations with respect to its ability to fund current planned operations are based on estimates that are subject to risks and uncertainties. If actual results are different from management's estimates, the Company may need to seek additional cash resources through strategic or financing opportunities sooner than would otherwise be expected. However, there is no guarantee that any of these strategic or financing opportunities will be executed or executed on favorable terms, and some could be dilutive to existing stockholders. If the Company is unable to obtain additional cash resources on a timely basis, it may be forced to significantly curtail, delay, or discontinue one or more of its planned research or development programs or be unable to expand its operations or commercialize products following marketing approval.