DEBT - Summary of Total Unsecured Notes Payable Outstanding (Details) $ in Thousands				6 Months Ended
		Sep. 19, 2014 USD ($)	Aug. 19, 2014	Jun. 30, 2015 USD ($) Extension_Option	Dec. 31, 2014 USD ($)
Debt Instrument [Line Items]
Unsecured notes payable				$ 450,000	$ 250,000
American Assets Trust, L.P.
Debt Instrument [Line Items]
Unsecured notes payable				450,000	250,000
American Assets Trust, L.P. | Term Loan
Debt Instrument [Line Items]
Unsecured notes payable				$ 100,000	100,000
Stated Maturity Date	[1]			Jan. 09, 2019
Debt extension options | Extension_Option				3
American Assets Trust, L.P. | Senior Guaranteed Notes, Series A
Debt Instrument [Line Items]
Unsecured notes payable				$ 150,000	150,000
Stated Interest Rate	[2]			4.04%
Stated Maturity Date				Oct. 31, 2021
American Assets Trust, L.P. | Senior Guaranteed Notes, Series B
Debt Instrument [Line Items]
Unsecured notes payable				$ 100,000	0
Stated Interest Rate				4.45%
Stated Maturity Date				Feb. 02, 2025
American Assets Trust, L.P. | Senior Guaranteed Notes, Series C
Debt Instrument [Line Items]
Unsecured notes payable				$ 100,000	$ 0
Stated Interest Rate				4.50%
Stated Maturity Date				Apr. 01, 2025
Interest Rate Swap | American Assets Trust, L.P.
Debt Instrument [Line Items]
Derivative fixed interest rate (in percent)				3.08%
Forward Contracts | American Assets Trust, L.P.
Debt Instrument [Line Items]
Derivative contract term			7 years
Gain on derivative settlement		$ 1,600
Effective rate of debt instrument (in percent)				3.88%

[1] The Operating Partnership has an option to extend the term loan up to three times, with each such extension for a 12-month period. The foregoing extension options are exercisable by us subject to the satisfaction of certain conditions.

[2] The Operating Partnership entered into a one-month forward-starting seven-year swap contract on August 19, 2014, which was settled on September 19, 2014 at a gain of approximately $1.6 million. The forward-starting seven-year swap contract was deemed to be a highly effective cash flow hedge, accordingly, the effective interest rate is approximately 3.88% per annum.