Cash and cash equivalents maturity period.

No definition available.

Name:	atra_CashAndCashEquivalentsMaturityPeriod
Namespace Prefix:	atra_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Defined contribution plan contributions by employer.

+ References

No definition available.

+ Details

Name:	atra_DefinedContributionPlanContributionsByEmployer
Namespace Prefix:	atra_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Investment maturity period.

+ References

No definition available.

+ Details

Name:	atra_InvestmentMaturityPeriod
Namespace Prefix:	atra_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

License and collaboration revenue.

+ References

No definition available.

+ Details

Name:	atra_LicenseAndCollaborationRevenue
Namespace Prefix:	atra_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Payment Received Upon Achievement of Certain Milestones

+ References

No definition available.

+ Details

Name:	atra_PaymentReceivedUponAchievementOfCertainMilestones
Namespace Prefix:	atra_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Significant accounting policies.

+ References

No definition available.

+ Details

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

- Definition

Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

+ References

No definition available.

+ Details

Name:	us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage employer matches of the employee's percentage contribution matched.

+ References

No definition available.

+ Details

Name:	us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Description of defined contribution pension and other postretirement plans.

+ References

No definition available.

+ Details

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

- Definition

The aggregate amount of write-downs for impairments recognized during the period for long lived assets held for use (including those held for disposal by means other than sale).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=109226691&loc=d3e2921-110230

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 4
-URI https://asc.fasb.org/extlink&oid=126905981&loc=d3e2420-110228

+ Details

Name:	us-gaap_ImpairmentOfLongLivedAssetsHeldForUse
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 18
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8672-108599

+ Details

Name:	us-gaap_NumberOfOperatingSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

+ References

+ Details

Name:	us-gaap_NumberOfReportableSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

+ References

No definition available.

+ Details

Name:	us-gaap_PropertyPlantAndEquipmentUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(iii)
-URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=atra_BayerLicenseAgreementBayerTechTransferAgreementAndBayerManufacturingAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=atra_PierreFabreCommercializationAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Summary of Significant Accounting Policies - Additional Information (Detail) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2023 USD ($)	Dec. 31, 2022 USD ($) Segment	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Significant Accounting Policies [Line Items]
Number of reportable segments \| Segment		1
Number of operating segments \| Segment		1
License and collaboration revenue		$ 63,573	$ 20,340	$ 0
Cash and cash equivalents maturity period		90 days
Investment maturity period		90 days
Impairment of long-lived assets		$ 0
Expected dividend yield		0.00%	0.00%	0.00%
Defined contribution plan, plan name		401(k)
Defined contribution plan, matching contribution percentage		50.00%
Defined contribution plan, maximum percentage of an individual's eligible earnings		6.00%
Defined contribution plan contributions by employer		$ 2,300	$ 2,600	$ 2,100
Minimum
Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life		3 years
Maximum
Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life		5 years
Bayer Agreements
Significant Accounting Policies [Line Items]
License and collaboration revenue		$ 61,800
Pierre Fabre Commercialization Agreement
Significant Accounting Policies [Line Items]
License and collaboration revenue		$ 1,800
Pierre Fabre Commercialization Agreement \| Subsequent Event [Member]
Significant Accounting Policies [Line Items]
Payment received upon achievement of certain milestones	$ 40,000