DEBT - Narrative (Details)						9 Months Ended
	Jan. 05, 2023 USD ($) extension	Jan. 05, 2022 USD ($) extension	Jan. 26, 2021 USD ($)	Jan. 09, 2019 extension	Jan. 09, 2018 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Jan. 04, 2023 USD ($)	Jan. 14, 2022 interest_rate_swap_agreement
Debt Instrument [Line Items]
Repayment of unsecured term loan						$ 150,000,000	$ 0
Repayments of line of credit						36,000,000	0
Unsecured line of credit, net
Debt Instrument [Line Items]
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 unsecured leverage ratio		175.00%
Maximum unsecured leverage ratio		60.00%
Maximum recourse indebtedness of total asset value		15.00%
Third Amended and Restated Credit Facility | Unsecured line of credit, net
Debt Instrument [Line Items]
Percentage annual distributions cannot exceed funds from operations		95.00%
American Assets Trust, L.P.
Debt Instrument [Line Items]
Repayment of unsecured term loan						150,000,000	0
Repayments of line of credit						$ 36,000,000	$ 0
American Assets Trust, L.P. | Unsecured term loans, net | Base Rate
Debt Instrument [Line Items]
Minimum base rate	0.00%
American Assets Trust, L.P. | Unsecured term loans, net | Federal Funds Rate
Debt Instrument [Line Items]
Basis spread on variable rate	0.50%
American Assets Trust, L.P. | Unsecured term loans, net | Secured Overnight Financing Rate
Debt Instrument [Line Items]
Basis spread on variable rate	1.00%
American Assets Trust, L.P. | Unsecured term loans, net | Minimum | Secured Overnight Financing Rate
Debt Instrument [Line Items]
Basis spread on variable rate	1.20%
American Assets Trust, L.P. | Unsecured term loans, net | Maximum | Secured Overnight Financing Rate
Debt Instrument [Line Items]
Basis spread on variable rate	1.90%
American Assets Trust, L.P. | Unsecured line of credit, net | Minimum | Secured Overnight Financing Rate | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate		1.05%
American Assets Trust, L.P. | Unsecured line of credit, net | Maximum | Secured Overnight Financing Rate | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate		1.50%
American Assets Trust, L.P. | 3.375% Senior Unsecured Notes
Debt Instrument [Line Items]
Stated Interest Rate			3.375%
Note offering percent			0.98935
Weighted average yield of investment			3.502%
Proceeds from debt, net of issuance costs			$ 489,700,000
American Assets Trust, L.P. | 3.375% Senior Unsecured Notes | Unsecured term loans, net
Debt Instrument [Line Items]
Face amount of debt			500,000,000
Stated Interest Rate						3.375%
American Assets Trust, L.P. | Senior Guaranteed Notes, Series A | Unsecured term loans, net
Debt Instrument [Line Items]
Repayment of unsecured term loan			150,000,000
Make whole payment			3,900,000
American Assets Trust, L.P. | Second Amended and Restated Credit Facility
Debt Instrument [Line Items]
Revolving credit facility borrowing limit, maximum borrowing capacity					$ 450,000,000
Additional borrowing capacity					250,000,000
American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Unsecured term loans, net
Debt Instrument [Line Items]
Revolving credit facility borrowing limit, maximum borrowing capacity					$ 100,000,000
American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Unsecured term loans, net | London Interbank Offered Rate
Debt Instrument [Line Items]
Basis spread on variable rate					1.00%
American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Unsecured term loans, net | Federal Funds Rate
Debt Instrument [Line Items]
Basis spread on variable rate		0.50%			0.50%
American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Unsecured term loans, net | Secured Overnight Financing Rate
Debt Instrument [Line Items]
Basis spread on variable rate		1.00%
American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Unsecured term loans, net | Minimum | London Interbank Offered Rate
Debt Instrument [Line Items]
Basis spread on variable rate					1.30%
American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Unsecured term loans, net | Minimum | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate					0.30%
American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Unsecured term loans, net | Maximum | London Interbank Offered Rate
Debt Instrument [Line Items]
Basis spread on variable rate					1.90%
American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Unsecured term loans, net | Maximum | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate					0.90%
American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Unsecured line of credit, net
Debt Instrument [Line Items]
Repayments of line of credit			$ 100,000,000
American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Unsecured line of credit, net | Revolving Credit Facility
Debt Instrument [Line Items]
Revolving credit facility borrowing limit, maximum borrowing capacity					$ 350,000,000
American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Unsecured line of credit, net | Minimum | London Interbank Offered Rate | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate					1.05%
American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Unsecured line of credit, net | Minimum | Base Rate | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate					0.10%
American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Unsecured line of credit, net | Maximum | London Interbank Offered Rate | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate					1.50%
American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Unsecured line of credit, net | Maximum | Base Rate | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate					0.50%
American Assets Trust, L.P. | Term Loan B
Debt Instrument [Line Items]
Term of debt instrument					7 years
American Assets Trust, L.P. | Term Loan B | Minimum | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate					0.70%
American Assets Trust, L.P. | Term Loan B | Maximum | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate					1.35%
American Assets Trust, L.P. | Term Loan B | Unsecured term loans, net | First Year
Debt Instrument [Line Items]
Derivative fixed interest rate	5.47%
American Assets Trust, L.P. | Term Loan B | Unsecured term loans, net | Second Year
Debt Instrument [Line Items]
Derivative fixed interest rate	5.57%
American Assets Trust, L.P. | Term Loan B | Unsecured term loans, net | Base Rate
Debt Instrument [Line Items]
Minimum base rate					0.00%
American Assets Trust, L.P. | Term Loan B | Unsecured term loans, net | Federal Funds Rate
Debt Instrument [Line Items]
Basis spread on variable rate					0.50%
American Assets Trust, L.P. | Term Loan B | Unsecured term loans, net | Eurodollar
Debt Instrument [Line Items]
Basis spread on variable rate					1.00%
American Assets Trust, L.P. | Term Loan B | Unsecured term loans, net | Minimum | London Interbank Offered Rate
Debt Instrument [Line Items]
Basis spread on variable rate					1.20%
American Assets Trust, L.P. | Term Loan B | Unsecured term loans, net | Maximum | London Interbank Offered Rate
Debt Instrument [Line Items]
Basis spread on variable rate					1.70%
American Assets Trust, L.P. | Term Loan B & Term Loan C
Debt Instrument [Line Items]
Debt extension options | extension	1
Extension term	12 months
American Assets Trust, L.P. | Term Loan B & Term Loan C | Unsecured term loans, net
Debt Instrument [Line Items]
Face amount of debt	$ 225,000,000				$ 150,000,000			$ 150,000,000
Debt extension options | extension	1
Extension term	12 months
American Assets Trust, L.P. | Term Loan B & Term Loan C | Unsecured term loans, net | Minimum | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate	0.20%
American Assets Trust, L.P. | Term Loan B & Term Loan C | Unsecured term loans, net | Maximum | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate	0.90%
American Assets Trust, L.P. | First Amendment To Second Amended And Restated Credit Facility | Minimum | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate				0.20%
American Assets Trust, L.P. | First Amendment To Second Amended And Restated Credit Facility | Maximum | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate				0.70%
American Assets Trust, L.P. | First Amendment To Second Amended And Restated Credit Facility | Unsecured term loans, net
Debt Instrument [Line Items]
Debt extension options | extension				3
Extension term				1 year
American Assets Trust, L.P. | First Amendment To Second Amended And Restated Credit Facility | Unsecured term loans, net | Federal Funds Rate
Debt Instrument [Line Items]
Basis spread on variable rate				0.50%
American Assets Trust, L.P. | First Amendment To Second Amended And Restated Credit Facility | Unsecured term loans, net | Eurodollar
Debt Instrument [Line Items]
Basis spread on variable rate				1.00%
American Assets Trust, L.P. | First Amendment To Second Amended And Restated Credit Facility | Unsecured term loans, net | Minimum | London Interbank Offered Rate
Debt Instrument [Line Items]
Basis spread on variable rate				1.20%
American Assets Trust, L.P. | First Amendment To Second Amended And Restated Credit Facility | Unsecured term loans, net | Maximum | London Interbank Offered Rate
Debt Instrument [Line Items]
Basis spread on variable rate				1.70%
American Assets Trust, L.P. | Third Amended and Restated Credit Facility
Debt Instrument [Line Items]
Revolving credit facility borrowing limit, maximum borrowing capacity		$ 500,000,000
Additional borrowing capacity		$ 400,000,000
American Assets Trust, L.P. | Third Amended and Restated Credit Facility | Interest Rate Swap
Debt Instrument [Line Items]
Derivative fixed interest rate									2.70%
Number of interest rate swap agreements | interest_rate_swap_agreement									2
American Assets Trust, L.P. | Third Amended and Restated Credit Facility | Unsecured term loans, net
Debt Instrument [Line Items]
Debt extension options | extension		2
Extension term		6 months
Revolving credit facility borrowing limit, maximum borrowing capacity		$ 100,000,000
American Assets Trust, L.P. | Third Amended and Restated Credit Facility | Unsecured term loans, net | Base Rate
Debt Instrument [Line Items]
Minimum base rate		1.00%
American Assets Trust, L.P. | Third Amended and Restated Credit Facility | Unsecured term loans, net | Minimum | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate		0.20%
American Assets Trust, L.P. | Third Amended and Restated Credit Facility | Unsecured term loans, net | Minimum | Secured Overnight Financing Rate
Debt Instrument [Line Items]
Basis spread on variable rate		1.20%
American Assets Trust, L.P. | Third Amended and Restated Credit Facility | Unsecured term loans, net | Maximum | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate		0.70%
American Assets Trust, L.P. | Third Amended and Restated Credit Facility | Unsecured term loans, net | Maximum | Secured Overnight Financing Rate
Debt Instrument [Line Items]
Basis spread on variable rate		1.70%
American Assets Trust, L.P. | Third Amended and Restated Credit Facility | Unsecured line of credit, net
Debt Instrument [Line Items]
Debt issuance costs, net, revolving credit facility						$ 1,500,000
Weighted average interest rate, revolving credit facility						6.12%
American Assets Trust, L.P. | Third Amended and Restated Credit Facility | Unsecured line of credit, net | Revolving Credit Facility
Debt Instrument [Line Items]
Revolving credit facility borrowing limit, maximum borrowing capacity		$ 400,000,000
American Assets Trust, L.P. | Third Amended and Restated Credit Facility | Unsecured line of credit, net | Minimum | Base Rate | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate		0.10%
American Assets Trust, L.P. | Third Amended and Restated Credit Facility | Unsecured line of credit, net | Maximum | Base Rate | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate		0.50%