DEBT - Narrative (Details)					3 Months Ended
	Jan. 05, 2022 USD ($) extension	Jan. 26, 2021 USD ($)	Jan. 09, 2019 extension	Jan. 09, 2018 USD ($)	Mar. 31, 2022 USD ($)	Mar. 31, 2021 USD ($)	Jan. 14, 2022	Mar. 01, 2018
Debt Instrument [Line Items]
Repayments of unsecured debt					$ 0	$ 155,375,000
Loss on early extinguishment of debt					0	(4,271,000)
Repayments of line of credit					0	100,000,000
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%
Maximum unsecured leverage ratio	60.00%
Maximum recourse indebtedness of total asset value	15.00%
Minimum fixed charge coverage ratio covenant threshold	1.50
Minimum unsecured leverage ratio	175.00%
American Assets Trust, L.P.
Debt Instrument [Line Items]
Repayments of unsecured debt					0	155,375,000
Loss on early extinguishment of debt					0	(4,271,000)
Repayments of line of credit					$ 0	$ 100,000,000
American Assets Trust, L.P. | Minimum | London Interbank Offered Rate (LIBOR) | Revolving Credit Facility | Unsecured line of credit, net
Debt Instrument [Line Items]
Basis spread on variable rate	1.05%
American Assets Trust, L.P. | Maximum | London Interbank Offered Rate (LIBOR) | Revolving Credit Facility | Unsecured line of credit, net
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 (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					3.38%
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 line of credit, net
Debt Instrument [Line Items]
Repayments of line of credit		$ 100,000,000
Debt issuance costs, net, revolving credit facility					$ (2,400,000)
American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Revolving Credit Facility | Unsecured line of credit, net
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 | London Interbank Offered Rate (LIBOR) | Unsecured term loans, net
Debt Instrument [Line Items]
Basis spread on variable rate				1.00%
American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Federal Funds Rate | Unsecured term loans, net
Debt Instrument [Line Items]
Basis spread on variable rate	0.50%			0.50%
American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate | Unsecured term loans, net
Debt Instrument [Line Items]
Basis spread on variable rate	1.00%
American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Minimum | London Interbank Offered Rate (LIBOR) | Unsecured term loans, net
Debt Instrument [Line Items]
Basis spread on variable rate				1.30%
American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Minimum | London Interbank Offered Rate (LIBOR) | Revolving Credit Facility | Unsecured line of credit, net
Debt Instrument [Line Items]
Basis spread on variable rate				1.05%
American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Minimum | Base Rate | Unsecured term loans, net
Debt Instrument [Line Items]
Basis spread on variable rate				0.30%
American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Minimum | Base Rate | Revolving Credit Facility | Unsecured line of credit, net
Debt Instrument [Line Items]
Basis spread on variable rate				0.10%
American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Maximum | London Interbank Offered Rate (LIBOR) | Unsecured term loans, net
Debt Instrument [Line Items]
Basis spread on variable rate				1.90%
American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Maximum | London Interbank Offered Rate (LIBOR) | Revolving Credit Facility | Unsecured line of credit, net
Debt Instrument [Line Items]
Basis spread on variable rate				1.50%
American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Maximum | Base Rate | Unsecured term loans, net
Debt Instrument [Line Items]
Basis spread on variable rate				0.90%
American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Maximum | Base Rate | Revolving Credit Facility | Unsecured line of credit, net
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 | Base Rate | Unsecured term loans, net
Debt Instrument [Line Items]
Minimum base rate				0.00%
American Assets Trust, L.P. | Term Loan B | Federal Funds Rate | Unsecured term loans, net
Debt Instrument [Line Items]
Basis spread on variable rate				0.50%
American Assets Trust, L.P. | Term Loan B | Eurodollar | Unsecured term loans, net
Debt Instrument [Line Items]
Basis spread on variable rate				1.00%
American Assets Trust, L.P. | Term Loan B | Minimum | London Interbank Offered Rate (LIBOR) | Unsecured term loans, net
Debt Instrument [Line Items]
Basis spread on variable rate				1.20%
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 | London Interbank Offered Rate (LIBOR) | Unsecured term loans, net
Debt Instrument [Line Items]
Basis spread on variable rate				1.70%
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%			2.65%
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 | 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 | Federal Funds Rate | Unsecured term loans, net
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 | Eurodollar | Unsecured term loans, net
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 | Minimum | London Interbank Offered Rate (LIBOR) | Unsecured term loans, net
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 | 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 | London Interbank Offered Rate (LIBOR) | Unsecured term loans, net
Debt Instrument [Line Items]
Basis spread on variable rate			1.70%
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. | 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 | 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 line of credit, net
Debt Instrument [Line Items]
Weighted average interest rate, revolving credit facility					1.24%
American Assets Trust, L.P. | Third Amended and Restated Credit Facility | Revolving Credit Facility | Unsecured line of credit, net
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 | Base Rate | Unsecured term loans, net
Debt Instrument [Line Items]
Minimum base rate	1.00%
American Assets Trust, L.P. | Third Amended and Restated Credit Facility | Minimum | Base Rate | Unsecured term loans, net
Debt Instrument [Line Items]
Basis spread on variable rate	0.20%
American Assets Trust, L.P. | Third Amended and Restated Credit Facility | Minimum | Base Rate | Revolving Credit Facility | Unsecured line of credit, net
Debt Instrument [Line Items]
Basis spread on variable rate	0.10%
American Assets Trust, L.P. | Third Amended and Restated Credit Facility | Minimum | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate | Unsecured term loans, net
Debt Instrument [Line Items]
Basis spread on variable rate	1.20%
American Assets Trust, L.P. | Third Amended and Restated Credit Facility | Maximum | Base Rate | Unsecured term loans, net
Debt Instrument [Line Items]
Basis spread on variable rate	0.70%
American Assets Trust, L.P. | Third Amended and Restated Credit Facility | Maximum | Base Rate | Revolving Credit Facility | Unsecured line of credit, net
Debt Instrument [Line Items]
Basis spread on variable rate	0.50%
American Assets Trust, L.P. | Third Amended and Restated Credit Facility | Maximum | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate | Unsecured term loans, net
Debt Instrument [Line Items]
Basis spread on variable rate	1.70%
American Assets Trust, L.P. | Third Amended and Restated Credit Facility | Interest Rate Swap
Debt Instrument [Line Items]
Derivative fixed interest rate (in percent)							2.70%