DEBT - Summary of Total Secured Notes Payable Outstanding (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Debt issuance costs, net	$ (543)	$ 0
Debt issuance costs, accumulated amortization	1,527	0
American Assets Trust, L.P. | Secured notes payable, net
Debt Instrument [Line Items]
Long-term Debt, Principal Balance	111,000	111,000
Debt issuance costs, net	(45)	(77)
Total Debt Outstanding	110,955	110,923
Debt issuance costs, accumulated amortization	376	345
American Assets Trust, L.P. | City Center Bellevue | Secured notes payable, net
Debt Instrument [Line Items]
Long-term Debt, Principal Balance	$ 111,000	$ 111,000
Stated Interest Rate	3.98%
Stated Maturity Date	Nov. 01, 2022