Acquisition costs capitalized.

No definition available.

Name:	aat_AcquisitionCostCapitalized
Namespace Prefix:	aat_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Purchase Price Seller Credits, Contractual Tenant Improvements

+ References

No definition available.

+ Details

Name:	aat_PurchasePriceSellerCreditsContractualTenantImprovements
Namespace Prefix:	aat_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Purchase Price Seller Credits, Future Rent Abatement

+ References

No definition available.

+ Details

Name:	aat_PurchasePriceSellerCreditsFutureRentAbatement
Namespace Prefix:	aat_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (a)(3)
-URI https://asc.fasb.org/extlink&oid=66006027&loc=d3e16265-109275

+ Details

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

- Definition

Area of a real estate property.

+ References

No definition available.

+ Details

Name:	us-gaap_AreaOfRealEstateProperty
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:areaItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

The cash outflow for purchases of and capital improvements on property, plant and equipment (capital expenditures), software, and other intangible assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (c)
-URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3213-108585

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 50
-Section 30
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=126928898&loc=d3e9212-128498

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 50
-Section 30
-Paragraph 2
-URI https://asc.fasb.org/extlink&oid=126928898&loc=d3e9215-128498

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 50
-Section 25
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=127000608&loc=d3e9135-128495

+ Details

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

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=aat_EastgateOfficeParkMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_LeaseAgreementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=srt_OfficeBuildingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=aat_CorporateCampusEastIIIMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=aat_BelSpring520Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

REAL ESTATE - Narrative (Details) $ in Millions				12 Months Ended
REAL ESTATE - Narrative (Details) $ in Millions	Mar. 08, 2022 USD ($) ft²	Sep. 10, 2021 USD ($) ft²	Jul. 07, 2021 USD ($) ft²	Dec. 31, 2022
Eastgate Office Park
Real Estate [Line Items]
Area of real estate property \| ft²			280,000
Purchase price consideration			$ 125.0
Acquisition cost capitalized			$ 0.2
Eastgate Office Park \| Leases \| Office Building
Real Estate [Line Items]
Weighted average useful life (in years)				3 years
Corporate Campus East III
Real Estate [Line Items]
Area of real estate property \| ft²		161,000
Purchase price consideration		$ 84.0
Acquisition cost capitalized		0.1
Corporate Campus East III \| Office Building
Real Estate [Line Items]
Purchase price seller credits, future rent abatement		1.1
Purchase price seller credits, contractual tenant improvements		$ 2.1
Bel-Spring 520
Real Estate [Line Items]
Area of real estate property \| ft²	93,000
Purchase price consideration	$ 45.5
Acquisition cost capitalized	0.1
Bel-Spring 520 \| Office Building
Real Estate [Line Items]
Purchase price seller credits, future rent abatement	0.1
Purchase price seller credits, contractual tenant improvements	$ 0.6