DEBT - Narrative (Details)						3 Months Ended		9 Months Ended
	Sep. 16, 2022 USD ($)	Jan. 05, 2022 USD ($) extension	Jan. 26, 2021 USD ($)	Jan. 09, 2019 extension	Jan. 09, 2018 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Jan. 14, 2022 interest_rate_swap_agreement	Dec. 31, 2021 USD ($)	Mar. 01, 2018
Debt Instrument [Line Items]
Repayments of unsecured debt								$ 0	$ 155,375,000
Loss on early extinguishment of debt						$ 0	$ 0	0	(4,271,000)
Repayments of line of credit								0	100,000,000
Line of credit						33,895,000		33,895,000			$ 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]
Repayments of unsecured debt								0	155,375,000
Loss on early extinguishment of debt						0	$ 0	0	(4,271,000)
Repayments of line of credit								0	$ 100,000,000
Line of credit						$ 33,895,000		$ 33,895,000			$ 0
American Assets Trust, L.P. | Unsecured line of credit, net | Minimum | London Interbank Offered Rate (LIBOR) | 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 | London Interbank Offered Rate (LIBOR) | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate		1.50%
American Assets Trust, L.P. | 5.08% City Center Bellevue, October 2027 | Secured notes payable, net
Debt Instrument [Line Items]
Extinguishment of debt	$ 111,000,000
Stated interest rate						5.08%		5.08%
American Assets Trust, L.P. | 5.08% City Center Bellevue, October 2027 | Mortgages | Nonrecourse
Debt Instrument [Line Items]
Face amount of debt	$ 75,000,000
Term of debt instrument	5 years
Stated interest rate	5.08%
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 (as a percent)			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%		3.375%
American Assets Trust, L.P. | Senior Guaranteed Notes, Series A | Unsecured term loans, net
Debt Instrument [Line Items]
Repayments of unsecured debt			150,000,000
Loss on early extinguishment of debt			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 (LIBOR)
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 (SOFR) Overnight Index Swap 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 (LIBOR)
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 (LIBOR)
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 (LIBOR) | 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 (LIBOR) | 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 | Interest Rate Swap
Debt Instrument [Line Items]
Derivative fixed interest rate (in percent)						3.15%		3.15%				2.65%
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 (LIBOR)
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 (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate					1.70%
American Assets Trust, L.P. | Term Loan B & Term Loan C | Unsecured term loans, net
Debt Instrument [Line Items]
Face amount of debt					$ 150,000,000
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 (LIBOR)
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 (LIBOR)
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
American Assets Trust, L.P. | Third Amended and Restated Credit Facility | Interest Rate Swap
Debt Instrument [Line Items]
Number of interest rate swap agreements | interest_rate_swap_agreement										2
Derivative fixed interest rate (in percent)										2.70%
American Assets Trust, L.P. | Third Amended and Restated Credit Facility | Unsecured term loans, net
Debt Instrument [Line Items]
Revolving credit facility borrowing limit, maximum borrowing capacity		$ 100,000,000
Debt extension options | extension		2
Extension term		6 months
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 (SOFR) Overnight Index Swap 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 (SOFR) Overnight Index Swap 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]
Line of credit						$ 36,000,000		$ 36,000,000
Debt issuance costs, net, revolving credit facility						$ 2,100,000		$ 2,100,000
Weighted average interest rate, revolving credit facility								2.26%
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%