SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	9 Months Ended
Sep. 30, 2023
Accounting Policies [Abstract]
Consolidation	Our consolidated financial statements include the accounts of the company, our Operating Partnership and our subsidiaries. The equity interests of other investors in our Operating Partnership are reflected as noncontrolling interests. The company follows the Financial Accounting Standards Board (the "FASB") guidance for determining whether an entity is a variable interest entity (“VIE”) and requires the performance of a qualitative rather than a quantitative analysis to determine the primary beneficiary of a VIE. Under this guidance, an entity would be required to consolidate a VIE if it has (i) the power to direct the activities that most significantly impact the entity’s economic performance and (ii) the obligation to absorb losses of the VIE or the right to receive benefits from the VIE that could be significant to the VIE. American Assets Trust, Inc. has concluded that the Operating Partnership is a VIE, and because American Assets Trust, Inc. has both the power and the rights to control the Operating Partnership, American Assets Trust, Inc. is the primary beneficiary and is required to continue to consolidate the Operating Partnership. Substantially all of the assets and liabilities of the company are related to the operating partnership VIE. All intercompany transactions and balances are eliminated in consolidation.
Basis of Accounting	The accompanying consolidated financial statements of the company and the Operating Partnership have been prepared in accordance with the rules applicable to Form 10-Q and include all information and footnotes required for interim financial statement presentation, but do not include all disclosures required under accounting principles generally accepted in the United States (“GAAP”) for annual financial statements. In the opinion of management, all adjustments (consisting of normal recurring adjustments, except as otherwise noted) considered necessary for a fair presentation have been included. These financial statements should be read in conjunction with the audited consolidated financial statements and notes therein included in the company's and Operating Partnership's annual report on Form 10-K for the year ended December 31, 2022.
Use of Estimates	The preparation of financial statements in conformity with GAAP requires us to make estimates and assumptions that in certain circumstances affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities, and revenues and expenses. These estimates are prepared using our best judgment, after considering past, current and expected events and economic conditions. Actual results could differ from these estimates.
Segment Information	Segment InformationSegment information is prepared on the same basis that our chief operating decision maker reviews information for operational decision-making purposes. We operate in four business segments: the acquisition, redevelopment, ownership and management of office real estate, retail real estate, multifamily real estate and mixed-use real estate. The products for our office segment primarily include rental of office space and other tenant services, including tenant reimbursements, parking and storage space rental. The products for our retail segment primarily include rental of retail space and other tenant services, including tenant reimbursements, parking and storage space rental. The products for our multifamily segment include rental of apartments and other tenant services. The products of our mixed-use segment include rental of retail space and other tenant services, including tenant reimbursements, parking and storage space rental and operation of a 369-room all-suite hotel.
Revenue Recognition and Accounts Receivable and Rent Concessions – COVID-19	Revenue Recognition and Accounts Receivable Our leases with tenants are classified as operating leases. Substantially all such leases contain fixed rent escalations which occur at specified times during the term of the lease. Base rents are recognized on a straight-line basis from when the tenant controls the space through the term of the related lease, net of valuation adjustments, based on management's assessment of credit, collection and other business risks. We make estimates of the collectability of our current accounts receivable and straight-line rents receivable which require significant judgment by management. The collectability of receivables is affected by numerous different factors including current economic conditions, the impact of tenant bankruptcies, the status of collectability of current cash rents receivable, tenants' recent and historical financial and operating results, changes in our tenants' credit ratings, communications between our operating personnel and tenants, the extent of security deposits and letters of credit held with respect to tenants, and the ability of tenants to perform under the terms of their lease agreement. The provision for doubtful accounts at September 30, 2023 and December 31, 2022 was approximately $1.3 million and $2.1 million, respectively. Rent Concessions – COVID-19 Due to the impacts of COVID-19, from 2020 through 2022 we provided lease concessions to certain tenants, primarily within the retail segment, in the form of rent deferrals and abatements. We assess each lease concession and determine whether it represents a lease modification under Accounting Standards Codification Topic 842, Leases ("ASC 842").
Recent Accounting Pronouncements	Recent Accounting Pronouncements In March 2020, the FASB issued ASU No. 2020-04, Reference Rate Reform (Topic 848), which provides companies with optional practical expedients to ease the accounting burden for contract modifications associated with transitioning away from LIBOR and other interbank offered rates that have been or are expected to be discontinued as part of reference rate reform. For hedges, the guidance generally allows changes to the reference rate and other critical terms without having to de-designate the hedging relationship, and permits the shortcut method to continue to be applied. For contract modifications, changes in the reference rate or other critical terms will be treated as a continuation of the prior contract. This guidance is generally only available until December 31, 2024. We are still evaluating the impact of reference rate reform and whether we will apply any of these practical expedients.
Fair Value Measurement	A fair value measurement is based on the assumptions that market participants would use in pricing an asset or liability. The hierarchy for inputs used in measuring fair value is as follows: 1.Level 1 Inputs—quoted prices in active markets for identical assets or liabilities 2.Level 2 Inputs—observable inputs other than quoted prices in active markets for identical assets and liabilities 3.Level 3 Inputs—unobservable inputs The carrying values of cash and cash equivalents, restricted cash, accounts receivable, accounts payable and accrued liabilities are reasonable estimates of fair value, using Level 1 inputs, because of the short-term nature of these instruments. In certain cases, the inputs used to measure fair value may fall into different levels of the fair value hierarchy. In such cases, for disclosure purposes, the level within which the fair value measurement is categorized is based on the lowest level input that is significant to the fair value measurement. We measure the fair value of our deferred compensation liability, which is included in other liabilities and deferred credits on the consolidated balance sheet, on a recurring basis using Level 2 inputs. We measure the fair value of this liability based on prices provided by independent market participants that are based on observable inputs using market-based valuation techniques. The fair value of the interest rate swap agreements are based on the estimated amounts we would receive or pay to terminate the contract at the reporting date and are determined using interest rate pricing models and interest rate related observable inputs. The changes in the fair value of the derivatives that are designated as cash flow hedges are being recorded in accumulated other comprehensive income (loss) and will be subsequently reclassified into earnings during the period in which the hedged forecasted transaction affects earnings. We incorporate credit valuation adjustments to appropriately reflect both our own non-performance risk and the respective counterparty’s non-performance risk in the fair value measurements. In adjusting the fair value of our derivative contracts for the effect of non-performance risk, we considered the impact of netting and any applicable credit enhancements, such as collateral postings, thresholds, mutual puts, and guarantees. Although we have determined that the majority of the inputs used to value our derivatives fall within Level 2 of the fair value hierarchy, the credit valuation adjustments associated with our derivatives utilize Level 3 inputs, such as estimates of current credit spreads to evaluate the likelihood of default by itself and its counterparties. However, as of September 30, 2023 we have assessed the significance of the impact of the credit valuation adjustments on the overall valuation of our derivative position and have determined that the credit valuation adjustments are not significant to the overall valuation of our derivative. As a result, we have determined that our derivative valuation in its entirety is classified in Level 2 of the fair value hierarchy.
Derivatives	The effective portion of changes in the fair value of the derivatives that are designated as cash flow hedges are being recorded in accumulated other comprehensive income and will be subsequently reclassified into earnings during the period in which the hedged forecasted transaction affects earnings for as long as hedged cash flows remain probable. During the next twelve months, we estimate the cash flow hedges in place will reduce interest expense by approximately $0.4 million.The valuation of these instruments is determined using widely accepted valuation techniques including discounted cash flow analysis on the expected cash flows of the derivative. This analysis reflects the contractual terms of the derivative, including the period to maturity, and counterparty credit risk and uses observable market-based inputs, including interest rate curves, and implied volatilities. The fair value of the interest rate swap is determined using the market standard methodology of netting the discounted future fixed cash receipts (or payments) and the discounted expected variable cash payments (or receipts). The variable cash payments (or receipts) are based on an expectation of future interest rates (forward curves) derived from observable market interest rate curves.

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)

9 Months Ended

Sep. 30, 2023

Our consolidated financial statements include the accounts of the company, our Operating Partnership and our subsidiaries. The equity interests of other investors in our Operating Partnership are reflected as noncontrolling interests.

The company follows the Financial Accounting Standards Board (the "FASB") guidance for determining whether an entity is a variable interest entity (“VIE”) and requires the performance of a qualitative rather than a quantitative analysis to determine the primary beneficiary of a VIE. Under this guidance, an entity would be required to consolidate a VIE if it has (i) the power to direct the activities that most significantly impact the entity’s economic performance and (ii) the obligation to absorb losses of the VIE or the right to receive benefits from the VIE that could be significant to the VIE. American Assets Trust, Inc. has concluded that the Operating Partnership is a VIE, and because American Assets Trust, Inc. has both the power and the rights to control the Operating Partnership, American Assets Trust, Inc. is the primary beneficiary and is required to continue to consolidate the Operating Partnership. Substantially all of the assets and liabilities of the company are related to the operating partnership VIE.

All intercompany transactions and balances are eliminated in consolidation.

Basis of Accounting

The accompanying consolidated financial statements of the company and the Operating Partnership have been prepared in accordance with the rules applicable to Form 10-Q and include all information and footnotes required for interim financial statement presentation, but do not include all disclosures required under accounting principles generally accepted in the United States (“GAAP”) for annual financial statements. In the opinion of management, all adjustments (consisting of normal recurring adjustments, except as otherwise noted) considered necessary for a fair presentation have been included. These financial statements should be read in conjunction with the audited consolidated financial statements and notes therein included in the company's and Operating Partnership's annual report on Form 10-K for the year ended December 31, 2022.

Use of Estimates

The preparation of financial statements in conformity with GAAP requires us to make estimates and assumptions that in certain circumstances affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities, and revenues and expenses. These estimates are prepared using our best judgment, after considering past, current and expected events and economic conditions. Actual results could differ from these estimates.

Segment Information

Segment InformationSegment information is prepared on the same basis that our chief operating decision maker reviews information for operational decision-making purposes. We operate in four business segments: the acquisition, redevelopment, ownership and management of office real estate, retail real estate, multifamily real estate and mixed-use real estate. The products for our office segment primarily include rental of office space and other tenant services, including tenant reimbursements, parking and storage space rental. The products for our retail segment primarily include rental of retail space and other tenant services, including tenant reimbursements, parking and storage space rental. The products for our multifamily segment include rental of apartments and other tenant services. The products of our mixed-use segment include rental of retail space and other tenant services, including tenant reimbursements, parking and storage space rental and operation of a 369-room all-suite hotel.

Revenue Recognition and Accounts Receivable and Rent Concessions – COVID-19

Revenue Recognition and Accounts Receivable

Our leases with tenants are classified as operating leases. Substantially all such leases contain fixed rent escalations which occur at specified times during the term of the lease. Base rents are recognized on a straight-line basis from when the tenant controls the space through the term of the related lease, net of valuation adjustments, based on management's assessment of credit, collection and other business risks.

We make estimates of the collectability of our current accounts receivable and straight-line rents receivable which require significant judgment by management. The collectability of receivables is affected by numerous different factors including current economic conditions, the impact of tenant bankruptcies, the status of collectability of current cash rents receivable, tenants' recent and historical financial and operating results, changes in our tenants' credit ratings, communications between our operating personnel and tenants, the extent of security deposits and letters of credit held with respect to tenants, and the ability of tenants to perform under the terms of their lease agreement. The provision for doubtful accounts at September 30, 2023 and December 31, 2022 was approximately $1.3 million and $2.1 million, respectively.

Rent Concessions – COVID-19

Due to the impacts of COVID-19, from 2020 through 2022 we provided lease concessions to certain tenants, primarily within the retail segment, in the form of rent deferrals and abatements. We assess each lease concession and determine whether it represents a lease modification under Accounting Standards Codification Topic 842, Leases ("ASC 842").

Recent Accounting Pronouncements

In March 2020, the FASB issued ASU No. 2020-04, Reference Rate Reform (Topic 848), which provides companies with optional practical expedients to ease the accounting burden for contract modifications associated with transitioning away from LIBOR and other interbank offered rates that have been or are expected to be discontinued as part of reference rate reform. For hedges, the guidance generally allows changes to the reference rate and other critical terms without having to de-designate the hedging relationship, and permits the shortcut method to continue to be applied. For contract modifications, changes in the reference rate or other critical terms will be treated as a continuation of the prior contract. This guidance is generally only available until December 31, 2024. We are still evaluating the impact of reference rate reform and whether we will apply any of these practical expedients.

Fair Value Measurement

A fair value measurement is based on the assumptions that market participants would use in pricing an asset or liability. The hierarchy for inputs used in measuring fair value is as follows:

1.Level 1 Inputs—quoted prices in active markets for identical assets or liabilities

2.Level 2 Inputs—observable inputs other than quoted prices in active markets for identical assets and liabilities

3.Level 3 Inputs—unobservable inputs

The carrying values of cash and cash equivalents, restricted cash, accounts receivable, accounts payable and accrued liabilities are reasonable estimates of fair value, using Level 1 inputs, because of the short-term nature of these instruments. In certain cases, the inputs used to measure fair value may fall into different levels of the fair value hierarchy. In such cases, for disclosure purposes, the level within which the fair value measurement is categorized is based on the lowest level input that is significant to the fair value measurement.

We measure the fair value of our deferred compensation liability, which is included in other liabilities and deferred credits on the consolidated balance sheet, on a recurring basis using Level 2 inputs. We measure the fair value of this liability based on prices provided by independent market participants that are based on observable inputs using market-based valuation techniques.

The fair value of the interest rate swap agreements are based on the estimated amounts we would receive or pay to terminate the contract at the reporting date and are determined using interest rate pricing models and interest rate related observable inputs. The changes in the fair value of the derivatives that are designated as cash flow hedges are being recorded in accumulated other comprehensive income (loss) and will be subsequently reclassified into earnings during the period in which the hedged forecasted transaction affects earnings.

We incorporate credit valuation adjustments to appropriately reflect both our own non-performance risk and the respective counterparty’s non-performance risk in the fair value measurements. In adjusting the fair value of our derivative contracts for the effect of non-performance risk, we considered the impact of netting and any applicable credit enhancements, such as collateral postings, thresholds, mutual puts, and guarantees.

Although we have determined that the majority of the inputs used to value our derivatives fall within Level 2 of the fair value hierarchy, the credit valuation adjustments associated with our derivatives utilize Level 3 inputs, such as estimates of current credit spreads to evaluate the likelihood of default by itself and its counterparties. However, as of September 30, 2023 we have assessed the significance of the impact of the credit valuation adjustments on the overall valuation of our derivative position and have determined that the credit valuation adjustments are not significant to the overall valuation of our derivative. As a result, we have determined that our derivative valuation in its entirety is classified in Level 2 of the fair value hierarchy.

Derivatives

The effective portion of changes in the fair value of the derivatives that are designated as cash flow hedges are being recorded in accumulated other comprehensive income and will be subsequently reclassified into earnings during the period in which the hedged forecasted transaction affects earnings for as long as hedged cash flows remain probable. During the next twelve months, we estimate the cash flow hedges in place will reduce interest expense by approximately $0.4 million.The valuation of these instruments is determined using widely accepted valuation techniques including discounted cash flow analysis on the expected cash flows of the derivative. This analysis reflects the contractual terms of the derivative, including the period to maturity, and counterparty credit risk and uses observable market-based inputs, including interest rate curves, and implied volatilities. The fair value of the interest rate swap is determined using the market standard methodology of netting the discounted future fixed cash receipts (or payments) and the discounted expected variable cash payments (or receipts). The variable cash payments (or receipts) are based on an expectation of future interest rates (forward curves) derived from observable market interest rate curves.

- Definition

Disclosure of accounting policy for segment reporting.

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