DEBT (Details)	Jul. 19, 2017 USD ($)	May 23, 2017 USD ($)	Mar. 01, 2017 USD ($)	Mar. 01, 2016	Jan. 09, 2014 USD ($) Extension_Option	Sep. 30, 2017 USD ($) Extension_Option		Dec. 31, 2016 USD ($)
Debt Instrument [Line Items]
Unsecured line of credit						$ 0		$ 20,000,000
Unsecured term loans, net | Term Loan A | Base Rate
Debt Instrument [Line Items]
Basis spread on federal funds rate				0.50%
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 | Amended and Restated Credit Facility | Base Rate
Debt Instrument [Line Items]
Basis spread on federal funds rate					0.50%
Basis spread on Eurodollar rate					1.00%
American Assets Trust, L.P.
Debt Instrument [Line Items]
Unsecured line of credit						$ 0		$ 20,000,000
American Assets Trust, L.P. | Term Loan A
Debt Instrument [Line Items]
Debt extension options | Extension_Option						1
American Assets Trust, L.P. | Amended and Restated Credit Facility
Debt Instrument [Line Items]
Revolving credit facility borrowing limit, maximum borrowing capacity					$ 350,000,000
Additional borrowing capacity					$ 250,000,000
American Assets Trust, L.P. | Amended and Restated Credit Facility | Minimum | Base Rate | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate					0.35%
American Assets Trust, L.P. | Amended and Restated Credit Facility | Maximum | Base Rate | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate					0.95%
American Assets Trust, L.P. | Unsecured term loans, net | Senior Guaranteed Notes, Series D
Debt Instrument [Line Items]
Face amount of debt			$ 250,000,000
Stated Interest Rate			4.29%			4.29%	[1]
Debt Instrument, Partial Repayment, Minimum Percentage of Principal			5.00%
Debt Instrument, Prepayment, Percentage of Principal Plus a Stated Amount			100.00%
American Assets Trust, L.P. | Unsecured term loans, net | Senior Guaranteed Notes, Series E
Debt Instrument [Line Items]
Face amount of debt		$ 100,000,000
Stated Interest Rate		4.24%				4.24%	[2]
Debt Instrument, Partial Repayment, Minimum Percentage of Principal		5.00%
Debt Instrument, Prepayment, Percentage of Principal Plus a Stated Amount		100.00%
American Assets Trust, L.P. | Unsecured term loans, net | Senior Guaranteed Notes, Series F
Debt Instrument [Line Items]
Face amount of debt	$ 100,000,000
Stated Interest Rate	3.78%					3.78%	[3]
Debt Instrument, Partial Repayment, Minimum Percentage of Principal	5.00%
Debt Instrument, Prepayment, Percentage of Principal Plus a Stated Amount	100.00%
American Assets Trust, L.P. | Unsecured term loans, net | Amended and Restated Credit Facility
Debt Instrument [Line Items]
Revolving credit facility borrowing limit, maximum borrowing capacity					$ 100,000,000
Debt extension options | Extension_Option					3
Extension term					12 months
American Assets Trust, L.P. | Unsecured term loans, net | 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 | 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 | 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 | 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 | Amended and Restated Credit Facility
Debt Instrument [Line Items]
Unsecured line of credit						$ 0
American Assets Trust, L.P. | Unsecured line of credit | Amended and Restated Credit Facility | Revolving Credit Facility
Debt Instrument [Line Items]
Revolving credit facility borrowing limit, maximum borrowing capacity					$ 250,000,000
Debt extension options | Extension_Option					2
Extension term					6 months
American Assets Trust, L.P. | Unsecured line of credit | 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 | Amended and Restated Credit Facility | Base Rate
Debt Instrument [Line Items]
Description of variable rate basis					base rate
Prime rate					prime rate
Federal funds rate					federal funds rate
Eurodollar rate					Eurodollar
American Assets Trust, L.P. | Unsecured line of credit | Amended and Restated Credit Facility | Minimum | London Interbank Offered Rate (LIBOR) | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate					1.35%
American Assets Trust, L.P. | Unsecured line of credit | Amended and Restated Credit Facility | Maximum | London Interbank Offered Rate (LIBOR) | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate					1.95%

[1] The Operating Partnership entered into forward-starting interest rate swap contracts on March 29, 2016 and April 7, 2016, which were settled on January 18, 2017 at a gain of approximately $10.4 million. The forward-starting interest swap rate contracts were deemed to be a highly effective cash flow hedge, accordingly, the effective interest rate is approximately 3.87% per annum.

[2] The Operating Partnership entered into a treasury lock contract on April 25, 2017, which was settled on May 11, 2017 at a gain of approximately $0.7 million. The treasury lock contract was deemed to be a highly effective cash flow hedge, accordingly, the effective interest rate is approximately 4.18% per annum.

[3] The Operating Partnership entered into a treasury lock contract on May 31, 2017, which was settled on June 23, 2017 at a loss 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 3.85% per annum.