Commitments and Contingencies - Schedule of Contract Services with FDB under Fujifilm MSA Minimum Amounts Set Forth (Detail) $ in Thousands	Jun. 30, 2022 USD ($)
Commitments and Contingencies Disclosure [Abstract]
2022	$ 12,530
2023	19,420
2024	14,085
2025	13,308
2026	9,605
2027	3,388
Total	$ 72,336

Recorded unconditional service obligation.

No definition available.

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

Recorded unconditional service obligation due in second year.

No definition available.

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

Recorded unconditional service obligations due after fifth year.

No definition available.

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

Recorded unconditional service obligations due in fifth year.

No definition available.

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

Recorded unconditional service obligations due in fourth year.

No definition available.

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

Recorded unconditional service obligations due within one year.

No definition available.

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

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

No definition available.

Name:	us-gaap_CommitmentsAndContingenciesDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration