Commitment and Contingencies - Schedule of Contract Services with FDB under Fujifilm MSA Minimum Amount Set Forth (Details) $ in Thousands	Dec. 31, 2024 USD ($)
Commitments and Contingencies Disclosure [Abstract]
2025	$ 13,308
2026	9,605
2027	3,388
Total	$ 26,301

Recorded unconditional service obligations due within third year.

No definition available.

Name:	atra_RecordedUnconditionalServiceObligationsDueWithinThirdYear
Namespace Prefix:	atra_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant