DEBT - Summary of Total Secured Notes Payable Outstanding (Details) - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Debt issuance costs, net		$ 0	$ (1,256)
Debt issuance costs, accumulated amortization		0	814
American Assets Trust, L.P. | Secured notes payable, net
Debt Instrument [Line Items]
Long-term Debt, Principal Balance		111,000	162,003
Debt issuance costs, net		(87)	(124)
Total Debt Outstanding		$ 110,913	161,879
Period of amortization schedule (in years)		30 years
Debt issuance costs, accumulated amortization		$ 334	449
American Assets Trust, L.P. | Secured notes payable, net | Torrey Reserve
Debt Instrument [Line Items]
Long-term Debt, Principal Balance	[1],[2]	$ 0	6,498
Stated Interest Rate	[1],[2]	6.36%
Stated Maturity Date	[1],[2]	Jun. 01, 2020
American Assets Trust, L.P. | Secured notes payable, net | Solana Beach Corporate Centre One To Two
Debt Instrument [Line Items]
Long-term Debt, Principal Balance	[1],[2]	$ 0	10,270
Stated Interest Rate	[1],[2]	5.91%
Stated Maturity Date	[1],[2]	Jun. 01, 2020
American Assets Trust, L.P. | Secured notes payable, net | Solana Beach Towne Centre
Debt Instrument [Line Items]
Long-term Debt, Principal Balance	[1],[2]	$ 0	34,235
Stated Interest Rate	[1],[2]	5.91%
Stated Maturity Date	[1],[2]	Jun. 01, 2020
American Assets Trust, L.P. | Secured notes payable, net | City Center Bellevue
Debt Instrument [Line Items]
Long-term Debt, Principal Balance	[3]	$ 111,000	$ 111,000
Stated Interest Rate	[3]	3.98%
Stated Maturity Date	[3]	Nov. 01, 2022

[1] Loan repaid in full, without premium or penalty, on March 2, 2020.

[2] Principal payments based on a 30-year amortization schedule.

[3] Interest only.