DEBT - Summary of Total Unsecured Notes Payable Outstanding (Details) - American Assets Trust, L.P. $ in Thousands								3 Months Ended
		Mar. 01, 2017	Jan. 18, 2017 USD ($)	Apr. 07, 2016	Mar. 29, 2016	Sep. 19, 2014 USD ($)	Aug. 19, 2014	Mar. 31, 2017 USD ($) Extension_Option		Dec. 31, 2016 USD ($)
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			$ 10,400			$ 1,600
Unsecured term loans, net
Debt Instrument [Line Items]
Long-term Debt, Principal Balance								$ 850,000		$ 600,000
Debt issuance costs, net								(5,248)		(3,650)
Total Debt Outstanding								844,752		596,350
Debt issuance costs, accumulated amortization								$ 4,675		4,317
Term Loan A
Debt Instrument [Line Items]
Debt extension options | Extension_Option								1
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 | Forward Contracts
Debt Instrument [Line Items]
Effective rate of debt instrument (in percent)								3.88%
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 | 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		100,000
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		50,000
Senior Guaranteed Notes, Series D
Debt Instrument [Line Items]
Stated Maturity Date		Mar. 01, 2027
Senior Guaranteed Notes, Series D | Forward Contracts
Debt Instrument [Line Items]
Effective rate of debt instrument (in percent)								3.87%
Senior Guaranteed Notes, Series D | Unsecured term loans, net
Debt Instrument [Line Items]
Stated Interest Rate		4.29%						4.29%	[3]
Stated Maturity Date								Mar. 01, 2027
Long-term Debt, Principal Balance								$ 250,000		$ 0

[1] The Operating Partnership has an option to extend the term loan up to one time, with such extension for a 12-month period. The foregoing extension option is 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 in accordance with GAAP is approximately 3.88% per annum.

[3] The Operating Partnership entered into forward-starting interest rate swap contracts on March 29, 2016 and April 7, 2016, which were settled on January 18, 2017 at a gain of approximately $10.4 million. The forward-starting interest swap rate contracts were deemed to be a highly effective cash flow hedge, accordingly, the effective interest rate in accordance with GAAP is approximately 3.87% per annum.