DEBT - Summary of Total Unsecured Notes Payable Outstanding (Details) - American Assets Trust, L.P. $ in Thousands									9 Months Ended
		May 02, 2016	Apr. 07, 2016	Mar. 29, 2016	Mar. 01, 2016	Jan. 29, 2016	Sep. 19, 2014 USD ($)	Aug. 19, 2014	Sep. 30, 2016 USD ($) Extension_Option	Dec. 31, 2015 USD ($)
Interest Rate Swap
Debt Instrument [Line Items]
Derivative contract term			10 years	10 years
Forward Contracts
Debt Instrument [Line Items]
Derivative contract term								7 years
Gain on derivative settlement							$ 1,600
Effective rate of debt instrument (in percent)									3.88%
Unsecured term loans, net
Debt Instrument [Line Items]
Long-term Debt, Principal Balance									$ 600,000	$ 450,000
Debt issuance costs, net									(3,992)	(3,387)
Total Debt Outstanding									596,008	446,613
Debt issuance costs, accumulated amortization									$ 3,975	2,999
Term Loan A
Debt Instrument [Line Items]
Debt extension options | Extension_Option									2
Term Loan A | Interest Rate Swap
Debt Instrument [Line Items]
Derivative fixed interest rate (in percent)									3.08%
Term Loan A | Unsecured term loans, net
Debt Instrument [Line Items]
Stated Maturity Date	[1]								Jan. 09, 2019
Long-term Debt, Principal Balance									$ 100,000	100,000
Senior Guaranteed Notes, Series A | Unsecured term loans, net
Debt Instrument [Line Items]
Stated Interest Rate	[2]								4.04%
Stated Maturity Date									Oct. 31, 2021
Long-term Debt, Principal Balance									$ 150,000	150,000
Senior Guaranteed Notes, Series B | Unsecured term loans, net
Debt Instrument [Line Items]
Stated Interest Rate									4.45%
Stated Maturity Date									Feb. 02, 2025
Long-term Debt, Principal Balance									$ 100,000	100,000
Senior Guaranteed Notes, Series C | Unsecured term loans, net
Debt Instrument [Line Items]
Stated Interest Rate									4.50%
Stated Maturity Date									Apr. 01, 2025
Long-term Debt, Principal Balance									$ 100,000	100,000
Term Loan B
Debt Instrument [Line Items]
Stated Maturity Date					Mar. 01, 2023	Mar. 01, 2023
Term Loan B | Interest Rate Swap
Debt Instrument [Line Items]
Derivative fixed interest rate (in percent)									3.15%
Term Loan B | Unsecured term loans, net
Debt Instrument [Line Items]
Stated Maturity Date									Mar. 01, 2023
Long-term Debt, Principal Balance									$ 100,000	0
Term Loan C
Debt Instrument [Line Items]
Stated Maturity Date		Mar. 01, 2023
Term Loan C | Interest Rate Swap
Debt Instrument [Line Items]
Derivative fixed interest rate (in percent)									3.14%
Term Loan C | Unsecured term loans, net
Debt Instrument [Line Items]
Stated Maturity Date									Mar. 01, 2023
Long-term Debt, Principal Balance									$ 50,000	$ 0

[1] The Operating Partnership has an option to extend the term loan up to two 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.