DEBT (Details)	Oct. 31, 2014 USD ($)	Jan. 09, 2014 USD ($) Extension_Option	Sep. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)
Debt Instrument [Line Items]
Unsecured line of credit			$ 25,000,000	$ 0
Unsecured line of credit | Future Year Period Two
Debt Instrument [Line Items]
Minimum fixed charge coverage ratio on revolving credit facility (in percent)		1.5
Minimum unsecured interest coverage ratio		175.00%
Unsecured line of credit | Amended and Restated Credit Facility
Debt Instrument [Line Items]
Maximum leverage ratio of revolving credit facility (in percent)		60.00%
Maximum unsecured leverage ratio		60.00%
Minimum tangible net worth		$ 721,160,000
Percent of net proceeds of any additional equity issuances in relation to net proceeds as of Offering		75.00%
Maximum recourse indebtedness to total asset value		15.00%
Percentage limit on annual distributions in relation to funds from operations		95.00%
Unsecured line of credit | Amended and Restated Credit Facility | Future Year Period One
Debt Instrument [Line Items]
Maximum secured leverage ratio on revolving credit facility (in percent)		45.00%
Unsecured line of credit | Amended and Restated Credit Facility | Future Year Period Two
Debt Instrument [Line Items]
Maximum secured leverage ratio on revolving credit facility (in percent)		40.00%
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%
Unsecured term loan | Amended and Restated Credit Facility | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Description of variable rate basis		LIBOR
American Assets Trust, L.P.
Debt Instrument [Line Items]
Unsecured line of credit			25,000,000	$ 0
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
Unsecured line of credit		$ 100,000,000
American Assets Trust, L.P. | Amended and Restated Credit Facility | Minimum | Revolving Credit Facility | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate		0.35%
American Assets Trust, L.P. | Amended and Restated Credit Facility | Maximum | Revolving Credit Facility | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate		0.95%
American Assets Trust, L.P. | Unsecured senior guaranteed notes | Note Purchase Agreement
Debt Instrument [Line Items]
Face amount of debt	$ 350,000,000
Partial debt repayment, minimum percentage of principal (in percent)	5.00%
Full debt repayment percentage of principal plus a Make-Whole Amount (in percent)	100.00%
American Assets Trust, L.P. | Senior Notes, Series A | Note Purchase Agreement
Debt Instrument [Line Items]
Face amount of debt	$ 150,000,000
Stated Interest Rate	4.04%
American Assets Trust, L.P. | Senior Notes, Series B | Note Purchase Agreement
Debt Instrument [Line Items]
Face amount of debt	$ 100,000,000
Stated Interest Rate	4.45%
American Assets Trust, L.P. | Senior Notes, Series C | Note Purchase Agreement
Debt Instrument [Line Items]
Face amount of debt	$ 100,000,000
Stated Interest Rate	4.50%
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 | 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 | Revolving Credit Facility | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Description of variable rate basis		LIBOR
American Assets Trust, L.P. | Unsecured line of credit | Amended and Restated Credit Facility | Minimum | Revolving Credit Facility | London Interbank Offered Rate (LIBOR)
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 | Revolving Credit Facility | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate		1.95%
American Assets Trust, L.P. | Unsecured term loan | Amended and Restated Credit Facility
Debt Instrument [Line Items]
Revolving credit facility borrowing limit, maximum borrowing capacity		$ 100,000,000
Unsecured line of credit			$ 25,000,000
Debt extension options | Extension_Option		3
Extension term		12 months
American Assets Trust, L.P. | Unsecured term loan | 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 loan | 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 loan | 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 loan | Amended and Restated Credit Facility | Maximum | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate		0.90%
American Assets Trust, L.P. | Interest Rate Swap | Cash Flow Hedging
Debt Instrument [Line Items]
Interest rate on derivative		3.08%