Debt Summary of Total Unsecured Notes Payable Outstanding (Details) $ in Thousands			12 Months Ended
		Aug. 19, 2014	Dec. 31, 2014 USD ($) Extension_Option	Dec. 31, 2013 USD ($)	Mar. 29, 2012
Debt Instrument [Line Items]
Unsecured notes payable			$ 250,000	$ 0
American Assets Trust, L.P.
Debt Instrument [Line Items]
Unsecured notes payable			250,000	0
Stated Interest Rate					3.94%
American Assets Trust, L.P. | Term Loan
Debt Instrument [Line Items]
Unsecured notes payable			$ 100,000	0
Stated Maturity Date	[1]		Jan. 09, 2019
Number of extensions available | Extension_Option			3
American Assets Trust, L.P. | Senior Guaranteed Notes, Series A
Debt Instrument [Line Items]
Unsecured notes payable			$ 150,000	$ 0
Stated Interest Rate	[2]		4.04%
Stated Maturity Date			Oct. 31, 2021
Interest Rate Swap
Debt Instrument [Line Items]
Fixed interest rate on derivative		2.1305%
Term of derivative contract		7 years
Interest Rate Swap | American Assets Trust, L.P.
Debt Instrument [Line Items]
Fixed interest rate on derivative			3.08%
Forward Contracts | American Assets Trust, L.P.
Debt Instrument [Line Items]
Term of derivative contract			1 month
Gain on derivatives			$ 1,600
Effective interest rate (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 the Operating Partnership subject to the satisfaction of certain conditions.

[2] The company 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 (see Note 9). 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.