Cover - USD ($)
3 Months Ended 12 Months Ended
Dec. 31, 2019
Dec. 31, 2019
Feb. 13, 2020
Jun. 30, 2019
Cover page.        
Document Type   10-K    
Document Annual Report   true    
Document Period End Date   Dec. 31, 2019    
Document Transition Report   false    
Entity File Number   001-35966    
Entity Registrant Name   bluebird bio, Inc.    
Entity Incorporation, State or Country Code   DE    
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    
Title of 12(b) Security   Common Stock, $0.01 par value per share    
Trading Symbol   BLUE    
Security Exchange Name   NASDAQ    
Entity Well-known Seasoned Issuer   Yes    
Entity Voluntary Filers No      
Entity Current Reporting Status   Yes    
Entity Interactive Data Current   Yes    
Entity Filer Category   Large Accelerated Filer    
Entity Small Business   false    
Entity Emerging Growth Company   false    
Entity Shell Company   false    
Entity Public Float       $ 7,025,034,290
Entity Common Stock, Shares Outstanding     55,611,565  
Documents Incorporated by Reference   Portions of the registrant’s definitive Proxy Statement relating to its 2020 Annual Meeting of Stockholders are incorporated by reference into Part III of this Annual Report on Form 10-K where indicated. Such Proxy Statement will be filed with the U.S. Securities and Exchange Commission within 120 days after the end of the fiscal year to which this report relates.    
Amendment Flag   false    
Document Fiscal Year Focus   2019    
Document Fiscal Period Focus   FY    
Entity Central Index Key   0001293971    
Current Fiscal Year End Date   --12-31