Out-license Agreements - Schedule of Deferred Revenue Activity (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023
License Collaboration And Manufacturing Agreements [Line Items]
Deferred revenue - long-term, December 31, 2024	$ 0	$ 37,562
Commercialization Revenue
License Collaboration And Manufacturing Agreements [Line Items]
Deferred revenue, December 31, 2023	115,395
Additions	105,235
Recognized into commercialization revenue	(125,538)
Deferred revenue December 31, 2024	95,092
Less: deferred revenue - current portion	(95,092)
Deferred revenue - long-term, December 31, 2024	$ 0

License, collaboration and manufacturing agreements.

No definition available.

Name:	atra_LicenseCollaborationAndManufacturingAgreementsLineItems
Namespace Prefix:	atra_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479837/606-10-45-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 8
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-8

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479837/606-10-45-2

+ Details

Name:	us-gaap_ContractWithCustomerLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable, classified as current.

+ References

+ Details

Name:	us-gaap_ContractWithCustomerLiabilityCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable, classified as noncurrent.

+ References

+ Details

Name:	us-gaap_ContractWithCustomerLiabilityNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of increase in deferred income not accounted for under Topic 606.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2B
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479432/944-30-50-2B

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 40
-Name Accounting Standards Codification
-Section 65
-Paragraph 2
-Subparagraph (g)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480016/944-40-65-2

+ Details

Name:	us-gaap_DeferredIncomeAddition
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of revenue recognized previously reported as deferred income not accounted for under Topic 606.

+ References

+ Details

Name:	us-gaap_DeferredIncomeRevenueRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	srt_ProductOrServiceAxis=atra_CommercializationRevenueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: