Annual report pursuant to Section 13 and 15(d)

Document and Entity Information

Document and Entity Information - USD ($)
12 Months Ended
Dec. 31, 2020
Feb. 18, 2021
Jun. 30, 2020
Cover [Abstract]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Dec. 31, 2020    
Document Fiscal Year Focus 2020    
Document Fiscal Period Focus FY    
Trading Symbol ATRA    
Entity Registrant Name ATARA BIOTHERAPEUTICS, INC.    
Entity Central Index Key 0001604464    
Current Fiscal Year End Date --12-31    
Entity Well-known Seasoned Issuer Yes    
Entity Current Reporting Status Yes    
Entity Voluntary Filers No    
Entity Filer Category Large Accelerated Filer    
Entity Common Stock, Shares Outstanding   83,614,853  
Entity Public Float     $ 906,895,284
Entity Shell Company false    
Entity Small Business false    
Entity Emerging Growth Company false    
Entity File Number 001-36548    
Entity Tax Identification Number 46-0920988    
Entity Address, Address Line One 611 Gateway Blvd.    
Entity Address, Address Line Two Suite 900    
Entity Address, City or Town South San Francisco    
Entity Address, State or Province CA    
Entity Address, Postal Zip Code 94080    
City Area Code 650    
Local Phone Number 278-8930    
Entity Incorporation, State or Country Code DE    
Title of 12(b) Security Common Stock, par value $0.0001 per share    
Security Exchange Name NASDAQ    
Entity Interactive Data Current Yes    
Document Annual Report true    
Document Transition Report false    
ICFR Auditor Attestation Flag true    
Documents Incorporated by Reference Portions of the Registrant’s definitive proxy statement relating to its 2021 Annual Meeting of Stockholders are incorporated by reference into Part III of this Report 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.