DEBT (Details) (USD $)	0 Months Ended
	Jan. 09, 2014	Oct. 31, 2014	Mar. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Unsecured line of credit			$ 20,000,000	$ 0
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 of 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 | Base Rate
Debt Instrument [Line Items]
Debt Instrument, Spread on Variable Rate Basis, Two	0.50%
Debt Instrument, Spread on Variable Rate Basis, Three	1.00%
Unsecured term loan | Amended and Restated Credit Facility | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Debt Instrument, Description of Variable Rate Basis	LIBOR
Future Year Period Two | Unsecured line of credit
Debt Instrument [Line Items]
Minimum fixed charge coverage ratio on revolving credit facility (in percent)	1.5
Minimum Unsecured Interest Coverage Ratio	175.00%
Future Year Period Two | Unsecured line of credit | Amended and Restated Credit Facility
Debt Instrument [Line Items]
Maximum secured leverage ratio on revolving credit facility (in percent)	40.00%
Future Year Period One | Unsecured line of credit | Amended and Restated Credit Facility
Debt Instrument [Line Items]
Maximum secured leverage ratio on revolving credit facility (in percent)	45.00%
American Assets Trust, L.P.
Debt Instrument [Line Items]
Unsecured line of credit			20,000,000	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
Line of Credit Facility, Allowable Additional Borrowing Capacity	250,000,000
Unsecured line of credit	100,000,000
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		4.00%
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		4.00%
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		5.00%
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	2
Debt Instrument, 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]
Debt Instrument, 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]
Debt Instrument, Description of Variable Rate Basis	base rate
Debt Instrument, Variable Rate Basis, One	prime rate
Debt Instrument, Variable Rate Basis, Two	federal funds rate
Debt Instrument, Variable Rate Basis, Three	Eurodollar
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
Debt extension options	3
Debt Instrument, Extension Term	12 months
Unsecured line of credit			$ 20,000,000
American Assets Trust, L.P. | Minimum | Amended and Restated Credit Facility | Base Rate | Revolving Credit Facility
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	0.35%
American Assets Trust, L.P. | Minimum | Unsecured line of credit | Amended and Restated Credit Facility | London Interbank Offered Rate (LIBOR) | Revolving Credit Facility
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.35%
American Assets Trust, L.P. | Minimum | Unsecured term loan | Amended and Restated Credit Facility | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.30%
American Assets Trust, L.P. | Minimum | Unsecured term loan | Amended and Restated Credit Facility | Base Rate
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	0.30%
American Assets Trust, L.P. | Maximum | Amended and Restated Credit Facility | Base Rate | Revolving Credit Facility
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	0.95%
American Assets Trust, L.P. | Maximum | Unsecured line of credit | Amended and Restated Credit Facility | London Interbank Offered Rate (LIBOR) | Revolving Credit Facility
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.95%
American Assets Trust, L.P. | Maximum | Unsecured term loan | Amended and Restated Credit Facility | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.90%
American Assets Trust, L.P. | Maximum | Unsecured term loan | Amended and Restated Credit Facility | Base Rate
Debt Instrument [Line Items]
Debt Instrument, 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%