| Document and Entity Information | Feb. 27, 2020 |
| Document And Entity Information [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Feb. 27, 2020 |
| Entity Registrant Name | Atara Biotherapeutics, Inc. |
| Entity Central Index Key | 0001604464 |
| Entity Emerging Growth Company | false |
| Entity File Number | 001-36548 |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 46-0920988 |
| Entity Address, Address Line One | 611 Gateway Boulevard |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of Each Class | Common Stock, par value $0.0001 per share |
| Trading Symbol | ATRA |
| Name of Each Exchange on Which Registered | NASDAQ |
