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DEBT - Narrative (Details) |  |  |  |  |  |  |  |  |  |  | 9 Months Ended |  |  |  |  |
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Feb. 03, 2025 USD ($) | Dec. 02, 2024 USD ($) | Sep. 17, 2024 USD ($) | Sep. 10, 2024 USD ($) | Jul. 19, 2024 USD ($) | Jul. 18, 2024 USD ($) | Jan. 05, 2023 USD ($) extension | Jan. 05, 2022 USD ($) extension | Jan. 26, 2021 USD ($) | Oct. 31, 2014 USD ($) | Sep. 30, 2025 USD ($) | Sep. 30, 2024 USD ($) | Sep. 09, 2024 USD ($) | Jul. 30, 2019 USD ($) | Jul. 19, 2017 USD ($) | May 23, 2017 USD ($) | Mar. 01, 2017 USD ($)
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Repayments of Unsecured Debt |  |  |  |  |  |  |  |  |  |  | $ 225,000,000 | $ 0 |  |  |  |  |
Repayment of unsecured line of credit |  |  |  |  |  |  |  |  |  |  | 0 | 100,000,000 |  |  |  |  |
Borrowings |  |  |  |  |  |  |  |  |  |  | 0 | 100,000,000 |  |  |  |  |
American Assets Trust, L.P. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Repayments of Unsecured Debt |  |  |  |  |  |  |  |  |  |  | 225,000,000 | 0 |  |  |  |  |
Repayment of unsecured line of credit |  |  |  |  |  |  |  |  |  |  | 0 | 100,000,000 |  |  |  |  |
Borrowings |  |  |  |  |  |  |  |  |  |  | $ 0 | $ 100,000,000 |  |  |  |  |
American Assets Trust, L.P. | Treasury Lock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Notional Amount |  |  |  | $ 150,000,000 |  |  |  |  |  |  |  |  | $ 150,000,000 |  |  |  |
Loss on derivatives |  |  |  | $ 1,300,000 |  |  |  |  |  |  |  |  |  |  |  |  |
3.375% Senior Notes | American Assets Trust, L.P. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stated Interest Rate |  |  |  |  |  |  |  |  | 3.375% |  |  |  |  |  |  |  |
3.375% Senior Notes | Unsecured term loans, net | American Assets Trust, L.P. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stated Interest Rate |  |  |  |  |  |  |  |  | 3.375% |  | 3.375% |  |  |  |  |  |
Face amount of debt |  |  |  |  |  |  |  |  | $ 500,000,000 |  |  |  |  |  |  |  |
Note offering percent |  |  |  |  |  |  |  |  | 0.98935 |  |  |  |  |  |  |  |
Effective interest rate |  |  |  |  |  |  |  |  | 3.502% |  |  |  |  |  |  |  |
Proceeds from debt, net of issuance costs |  |  |  |  |  |  |  |  | $ 489,700,000 |  |  |  |  |  |  |  |
Maximum aggregate debt ratio |  |  |  |  |  |  |  |  |  |  | 60.00% |  |  |  |  |  |
Minimum debt service ratio |  |  |  |  |  |  |  |  |  |  | 1.5 |  |  |  |  |  |
Maximum secured debt ratio |  |  |  |  |  |  |  |  |  |  | 40.00% |  |  |  |  |  |
Minimum maintenance of total unencumbered assets |  |  |  |  |  |  |  |  |  |  | 150.00% |  |  |  |  |  |
Senior Guaranteed Notes, Series A | Unsecured term loans, net | American Assets Trust, L.P. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Repayments of Unsecured Debt |  |  |  |  |  |  |  |  | 150,000,000 |  |  |  |  |  |  |  |
Make-whole payment |  |  |  |  |  |  |  |  | 3,900,000 |  |  |  |  |  |  |  |
Second Amended and Restated Credit Facility | Unsecured term loans, net | American Assets Trust, L.P. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Repayment of unsecured line of credit |  |  |  |  |  |  |  |  | $ 100,000,000 |  |  |  |  |  |  |  |
6.150% Senior Notes | American Assets Trust, L.P. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stated Interest Rate |  |  | 6.15% |  |  |  |  |  |  |  |  |  |  |  |  |  |
6.150% Senior Notes | American Assets Trust, L.P. | Treasury Lock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Effective interest rate |  |  |  |  |  |  |  |  |  |  | 6.209% |  |  |  |  |  |
6.150% Senior Notes | Unsecured term loans, net | American Assets Trust, L.P. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stated Interest Rate |  |  | 6.15% |  |  |  |  |  |  |  | 6.15% |  |  |  |  |  |
Face amount of debt |  |  | $ 525,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Note offering percent |  |  | 0.99671 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Effective interest rate |  |  | 6.194% |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from debt, net of issuance costs |  |  | $ 518,200,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Note Purchase Agreement | Senior Guaranteed Notes | American Assets Trust, L.P. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Face amount of debt |  |  |  |  |  |  |  |  |  | $ 350,000,000 |  |  |  |  |  |  |
Partial debt repayment, minimum percentage of principal |  |  |  |  |  |  |  |  |  | 5.00% |  |  |  |  |  |  |
Full debt repayment percentage of principal plus a make-whole amount |  |  |  |  |  |  |  |  |  | 100.00% |  |  |  |  |  |  |
Note Purchase Agreement | Senior Guaranteed Notes, Series A | American Assets Trust, L.P. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stated Interest Rate |  |  |  |  |  |  |  |  |  | 4.04% |  |  |  |  |  |  |
Face amount of debt |  |  |  |  |  |  |  |  |  | $ 150,000,000 |  |  |  |  |  |  |
Note Purchase Agreement | Series B Notes | American Assets Trust, L.P. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stated Interest Rate |  |  |  |  |  |  |  |  |  | 4.45% |  |  |  |  |  |  |
Face amount of debt |  |  |  |  |  |  |  |  |  | $ 100,000,000 |  |  |  |  |  |  |
Note Purchase Agreement | Senior Guaranteed Notes, Series C | American Assets Trust, L.P. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stated Interest Rate |  |  |  |  |  |  |  |  |  | 4.50% |  |  |  |  |  |  |
Face amount of debt |  |  |  |  |  |  |  |  |  | $ 100,000,000 |  |  |  |  |  |  |
Senior Guaranteed Notes, Series D | American Assets Trust, L.P. | Treasury Lock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Effective interest rate |  |  |  |  |  |  |  |  |  |  | 3.87% |  |  |  |  |  |
Senior Guaranteed Notes, Series D | Unsecured term loans, net | American Assets Trust, L.P. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stated Interest Rate |  |  |  |  |  |  |  |  |  |  | 4.29% |  |  |  |  |  | 4.29%
Face amount of debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 250,000,000
Senior Guaranteed Notes, Series E | American Assets Trust, L.P. | Treasury Lock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Effective interest rate |  |  |  |  |  |  |  |  |  |  | 4.18% |  |  |  |  |  |
Senior Guaranteed Notes, Series E | Unsecured term loans, net | American Assets Trust, L.P. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stated Interest Rate |  |  |  |  |  |  |  |  |  |  | 4.24% |  |  |  |  | 4.24% |
Face amount of debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 100,000,000 |
Senior Guaranteed Notes, Series F | Unsecured term loans, net | American Assets Trust, L.P. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stated Interest Rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3.78% |  |
Face amount of debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 100,000,000 |  |
Repayments of Unsecured Debt |  |  |  |  | $ 100,000,000 |  |  |  |  |  |  |  |  |  |  |  |
Borrowings |  |  |  |  |  | $ 100,000,000 |  |  |  |  |  |  |  |  |  |  |
Senior Guaranteed Notes, Series G | American Assets Trust, L.P. | Treasury Lock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Effective interest rate |  |  |  |  |  |  |  |  |  |  | 3.88% |  |  |  |  |  |
Senior Guaranteed Notes, Series G | Unsecured term loans, net | American Assets Trust, L.P. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stated Interest Rate |  |  |  |  |  |  |  |  |  |  | 3.91% |  |  | 3.91% |  |  |
Face amount of debt |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 150,000,000 |  |  |
Third Amended and Restated Credit Facility | American Assets Trust, L.P. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revolving credit facility borrowing limit, maximum borrowing capacity |  |  |  |  |  |  |  | $ 500,000,000 |  |  |  |  |  |  |  |  |
Third Amended and Restated Credit Facility | American Assets Trust, L.P. | Base Rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  |  |  |  | 1.00% |  |  |  |  |  |  |  |  |
Third Amended and Restated Credit Facility | Unsecured term loans, net | American Assets Trust, L.P. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revolving credit facility borrowing limit, maximum borrowing capacity |  |  |  |  |  |  |  | $ 100,000,000 |  |  |  |  |  |  |  |  |
Number of extensions available | extension |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |  |  |
Extension term |  |  |  |  |  |  |  | 6 months |  |  |  |  |  |  |  |  |
Third Amended and Restated Credit Facility | Unsecured term loans, net | American Assets Trust, L.P. | SOFR |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  |  |  |  | 1.00% |  |  |  |  |  |  |  |  |
Third Amended and Restated Credit Facility | Unsecured term loans, net | American Assets Trust, L.P. | Federal Funds Rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  |  |  |  | 0.50% |  |  |  |  |  |  |  |  |
Third Amended and Restated Credit Facility | Unsecured term loans, net | American Assets Trust, L.P. | Minimum | SOFR |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  |  |  |  | 1.20% |  |  |  |  |  |  |  |  |
Third Amended and Restated Credit Facility | Unsecured term loans, net | American Assets Trust, L.P. | Minimum | Base Rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  |  |  |  | 0.20% |  |  |  |  |  |  |  |  |
Third Amended and Restated Credit Facility | Unsecured term loans, net | American Assets Trust, L.P. | Maximum | SOFR |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  |  |  |  | 1.70% |  |  |  |  |  |  |  |  |
Third Amended and Restated Credit Facility | Unsecured term loans, net | American Assets Trust, L.P. | Maximum | Base Rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  |  |  |  | 0.70% |  |  |  |  |  |  |  |  |
Third Amended and Restated Credit Facility | Unsecured line of credit, net | American Assets Trust, L.P. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt issuance costs, net, revolving credit facility |  |  |  |  |  |  |  |  |  |  | $ 200,000 |  |  |  |  |  |
Weighted average interest rate |  |  |  |  |  |  |  |  |  |  | 5.53% |  |  |  |  |  |
Maximum leverage ratio of revolving credit facility |  |  |  |  |  |  |  | 60.00% |  |  |  |  |  |  |  |  |
Maximum secured leverage ratio on revolving credit facility |  |  |  |  |  |  |  | 40.00% |  |  |  |  |  |  |  |  |
Minimum fixed charge coverage ratio covenant threshold |  |  |  |  |  |  |  | 1.50 |  |  |  |  |  |  |  |  |
Minimum interest coverage ratio covenant threshold |  |  |  |  |  |  |  | 1.75 |  |  |  |  |  |  |  |  |
Maximum unsecured leverage ratio (in percentage) |  |  |  |  |  |  |  | 60.00% |  |  |  |  |  |  |  |  |
Maximum recourse indebtedness of total asset value |  |  |  |  |  |  |  | 15.00% |  |  |  |  |  |  |  |  |
Percentage annual distributions cannot exceed funds from operations |  |  |  |  |  |  |  | 95.00% |  |  |  |  |  |  |  |  |
Third Amended and Restated Credit Facility | Unsecured line of credit, net | American Assets Trust, L.P. | Revolving Credit Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revolving credit facility borrowing limit, maximum borrowing capacity |  |  |  |  |  |  |  | $ 400,000,000 |  |  |  |  |  |  |  |  |
Third Amended and Restated Credit Facility | Unsecured line of credit, net | American Assets Trust, L.P. | Revolving Credit Facility | Minimum | SOFR |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  |  |  |  | 1.05% |  |  |  |  |  |  |  |  |
Third Amended and Restated Credit Facility | Unsecured line of credit, net | American Assets Trust, L.P. | Revolving Credit Facility | Minimum | Base Rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  |  |  |  | 0.10% |  |  |  |  |  |  |  |  |
Third Amended and Restated Credit Facility | Unsecured line of credit, net | American Assets Trust, L.P. | Revolving Credit Facility | Maximum | SOFR |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  |  |  |  | 1.50% |  |  |  |  |  |  |  |  |
Third Amended and Restated Credit Facility | Unsecured line of credit, net | American Assets Trust, L.P. | Revolving Credit Facility | Maximum | Base Rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  |  |  |  | 0.50% |  |  |  |  |  |  |  |  |
Term Loan A | American Assets Trust, L.P. | Interest Rate Swap |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fixed interest rate on derivative |  |  |  |  |  |  |  |  |  |  | 2.70% |  |  |  |  |  |
Term Loan B | Unsecured term loans, net | American Assets Trust, L.P. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Face amount of debt |  |  |  |  |  |  | $ 150,000,000 |  |  |  |  |  |  |  |  |  |
Term Loan C | Unsecured term loans, net | American Assets Trust, L.P. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Face amount of debt |  |  |  |  |  |  | $ 75,000,000 |  |  |  |  |  |  |  |  |  |
Term Loan B & Term Loan C | Unsecured term loans, net | American Assets Trust, L.P. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of extensions available | extension |  |  |  |  |  |  | 1 |  |  |  |  |  |  |  |  |  |
Extension term |  |  |  |  |  |  | 12 months |  |  |  |  |  |  |  |  |  |
Series B Notes | Unsecured term loans, net | American Assets Trust, L.P. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Repayments of Unsecured Debt |  | $ 100,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Senior Guaranteed Notes, Series C | Unsecured term loans, net | American Assets Trust, L.P. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stated Interest Rate |  |  |  |  |  |  |  |  |  |  | 4.50% |  |  |  |  |  |
Repayments of Unsecured Debt | $ 100,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revolver Loan | Unsecured term loans, net | American Assets Trust, L.P. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Repayments of Unsecured Debt |  |  | $ 100,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |

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