DEBT - Narrative (Details)				6 Months Ended
		Jan. 09, 2019 Extension_Option	Jan. 09, 2018 USD ($) Extension_Option	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Debt Instrument [Line Items]
Unsecured line of credit, net				$ 98,948,000	$ 0
Unsecured term loans, net | Term Loan B | Federal Funds Rate
Debt Instrument [Line Items]
Basis spread on federal funds rate			0.50%
Unsecured term loans, net | Term Loan B | Eurodollar
Debt Instrument [Line Items]
Basis spread on Eurodollar rate			1.00%
Unsecured term loans, net | Term Loan C | Federal Funds Rate
Debt Instrument [Line Items]
Basis spread on federal funds rate			0.50%
Unsecured term loans, net | Term Loan C | Eurodollar
Debt Instrument [Line Items]
Basis spread on Eurodollar rate			1.00%
Unsecured term loans, net | Term Loan A | Federal Funds Rate
Debt Instrument [Line Items]
Basis spread on federal funds rate		0.50%
Unsecured term loans, net | Term Loan A | Eurodollar
Debt Instrument [Line Items]
Basis spread on Eurodollar rate		1.00%
Unsecured term loans, net | Second Amended and Restated Credit Facility | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Description of variable rate basis			LIBOR
Unsecured line of credit, net
Debt Instrument [Line Items]
Minimum fixed charge coverage ratio covenant threshold			1.50
Minimum unsecured leverage ratio			175.00%
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%
Unsecured line of credit, net | Second Amended and Restated Credit Facility | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate			1.00%
Unsecured line of credit, net | Second Amended and Restated Credit Facility | Base Rate
Debt Instrument [Line Items]
Basis spread on federal funds rate			0.50%
American Assets Trust, L.P.
Debt Instrument [Line Items]
Unsecured line of credit, net				98,948,000	0
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 C
Debt Instrument [Line Items]
Term of debt instrument			7 years
American Assets Trust, L.P. | Term Loan C | Minimum | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate			0.70%
American Assets Trust, L.P. | Term Loan C | Maximum | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate			1.35%
American Assets Trust, L.P. | Term Loan A | Minimum | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate		0.20%
American Assets Trust, L.P. | Term Loan A | Maximum | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate		0.70%
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. | Unsecured term loans, net
Debt Instrument [Line Items]
Long-term Debt, Principal Balance				1,200,000,000	1,200,000,000
American Assets Trust, L.P. | Unsecured term loans, net | Senior Guaranteed Notes, Series G
Debt Instrument [Line Items]
Long-term Debt, Principal Balance				$ 150,000,000	150,000,000
Stated Interest Rate	[1]			3.91%
Stated Maturity Date				Jul. 30, 2030
American Assets Trust, L.P. | Unsecured term loans, net | Term Loan B
Debt Instrument [Line Items]
Long-term Debt, Principal Balance				$ 100,000,000	100,000,000
Stated Maturity Date				Mar. 01, 2023
American Assets Trust, L.P. | Unsecured term loans, net | Term Loan B | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Description of variable rate basis			LIBOR
American Assets Trust, L.P. | Unsecured term loans, net | Term Loan B | Base Rate
Debt Instrument [Line Items]
Minimum base rate			0.00%
Prime rate			prime rate
Federal funds rate			federal funds rate
Eurodollar rate			Eurodollar
American Assets Trust, L.P. | Unsecured term loans, net | Term Loan B | Minimum | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate			1.20%
American Assets Trust, L.P. | Unsecured term loans, net | Term Loan B | Maximum | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate			1.70%
American Assets Trust, L.P. | Unsecured term loans, net | Term Loan C
Debt Instrument [Line Items]
Long-term Debt, Principal Balance				$ 50,000,000	50,000,000
Stated Maturity Date				Mar. 01, 2023
American Assets Trust, L.P. | Unsecured term loans, net | Term Loan C | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Description of variable rate basis			LIBOR
American Assets Trust, L.P. | Unsecured term loans, net | Term Loan C | Base Rate
Debt Instrument [Line Items]
Minimum base rate			0.00%
Prime rate			prime rate
Federal funds rate			federal funds rate
Eurodollar rate			Eurodollar
American Assets Trust, L.P. | Unsecured term loans, net | Term Loan C | Minimum | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate			1.20%
American Assets Trust, L.P. | Unsecured term loans, net | Term Loan C | Maximum | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate			1.70%
American Assets Trust, L.P. | Unsecured term loans, net | Term Loan A
Debt Instrument [Line Items]
Long-term Debt, Principal Balance				$ 100,000,000	$ 100,000,000
Stated Maturity Date				Jan. 09, 2021
Debt extension options | Extension_Option		3
Extension term		1 year
American Assets Trust, L.P. | Unsecured term loans, net | Term Loan A | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Description of variable rate basis		LIBOR
American Assets Trust, L.P. | Unsecured term loans, net | Term Loan A | Base Rate
Debt Instrument [Line Items]
Prime rate		prime rate
Federal funds rate		federal funds rate
Eurodollar rate		Eurodollar
American Assets Trust, L.P. | Unsecured term loans, net | Term Loan A | Minimum | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate		1.20%
American Assets Trust, L.P. | Unsecured term loans, net | Term Loan A | Maximum | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate		1.70%
American Assets Trust, L.P. | Unsecured term loans, net | Term Loan B & Term Loan C
Debt Instrument [Line Items]
Face amount of debt			$ 150,000,000
American Assets Trust, L.P. | Unsecured term loans, net | Second Amended and Restated Credit Facility
Debt Instrument [Line Items]
Revolving credit facility borrowing limit, maximum borrowing capacity			$ 100,000,000
American Assets Trust, L.P. | Unsecured term loans, net | Second Amended and Restated Credit Facility | Minimum | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate			1.30%
American Assets Trust, L.P. | Unsecured term loans, net | Second Amended and Restated Credit Facility | Minimum | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate			0.30%
American Assets Trust, L.P. | Unsecured term loans, net | Second Amended and Restated Credit Facility | Maximum | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate			1.90%
American Assets Trust, L.P. | Unsecured term loans, net | Second Amended and Restated Credit Facility | Maximum | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate			0.90%
American Assets Trust, L.P. | Unsecured line of credit, net | Second Amended and Restated Credit Facility
Debt Instrument [Line Items]
Unsecured line of credit, net				$ 100,000,000
Debt issuance costs, net, revolving credit facility				$ (1,100,000)
Weighted average interest rate, revolving credit facility				1.58%
American Assets Trust, L.P. | Unsecured line of credit, net | Second Amended and Restated Credit Facility | Revolving Credit Facility
Debt Instrument [Line Items]
Revolving credit facility borrowing limit, maximum borrowing capacity			$ 350,000,000
Debt extension options | Extension_Option			2
Extension term			6 months
American Assets Trust, L.P. | Unsecured line of credit, net | Second Amended and Restated Credit Facility | London Interbank Offered Rate (LIBOR) | Revolving Credit Facility
Debt Instrument [Line Items]
Description of variable rate basis			LIBOR
American Assets Trust, L.P. | Unsecured line of credit, net | Second Amended and Restated Credit Facility | Base Rate
Debt Instrument [Line Items]
Prime rate			prime rate
Federal funds rate			federal funds rate
American Assets Trust, L.P. | Unsecured line of credit, net | Second Amended and Restated Credit Facility | 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 | Second Amended and Restated Credit Facility | Minimum | Base Rate | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate			0.10%
American Assets Trust, L.P. | Unsecured line of credit, net | Second Amended and Restated Credit Facility | 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. | Unsecured line of credit, net | Second Amended and Restated Credit Facility | Maximum | Base Rate | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate			0.50%

[1] The Operating Partnership entered into a treasury lock contract on June 20, 2019, which was settled on July 17, 2019 at a gain of approximately $0.5 million. The treasury lock contract was deemed to be a highly effective cash flow hedge, accordingly, the effective interest rate is approximately 3.88% per annum.