DEBT (Details)				3 Months Ended
	Jan. 09, 2018 USD ($) Extension_Option	Mar. 01, 2016	Jan. 09, 2014	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Unsecured line of credit, net				$ 33,031,000	$ 0
Weighted average interest rate, revolving credit facility				3.40%
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 | 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	1.5
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 | 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				$ 33,031,000	$ 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. | Second Amended and Restated Credit Facility
Debt Instrument [Line Items]
Revolving credit facility borrowing limit, maximum borrowing capacity	$ 450,000,000
Additional borrowing capacity	$ 350,000,000
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 | 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 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 | 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%
American Assets Trust, L.P. | Unsecured line of credit, net | Amended and Restated Credit Facility
Debt Instrument [Line Items]
Unsecured line of credit, net				35,000,000
Debt issuance costs, net, revolving credit facility				$ (2,000,000)