DEBT - Summary of Total Secured Notes Payable Outstanding (Details) - American Assets Trust, L.P. - Secured notes payable, net - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Long-term Debt, Principal Balance		$ 205,047	$ 279,889
Debt issuance costs, net		(229)	(339)
Total Debt Outstanding		$ 204,818	279,550
Period of amortization schedule (in years)		30 years
Debt issuance costs, accumulated amortization		$ 857	1,191
Loma Palisades
Debt Instrument [Line Items]
Long-term Debt, Principal Balance	[1],[2]	$ 0	73,744
Stated Interest Rate	[1],[2]	6.09%
Stated Maturity Date	[1],[2]	Jul. 01, 2018
One Beach Street
Debt Instrument [Line Items]
Long-term Debt, Principal Balance	[1]	$ 21,900	21,900
Stated Interest Rate	[1]	3.94%
Stated Maturity Date	[1]	Apr. 01, 2019
Torrey Reserve North Court
Debt Instrument [Line Items]
Long-term Debt, Principal Balance	[3]	$ 19,723	20,023
Stated Interest Rate	[3]	7.22%
Stated Maturity Date	[3]	Jun. 01, 2019
Torrey Reserve
Debt Instrument [Line Items]
Long-term Debt, Principal Balance	[3]	$ 6,669	6,764
Stated Interest Rate	[3]	6.36%
Stated Maturity Date	[3]	Jun. 01, 2020
Solana Beach Corporate Centre One To Two
Debt Instrument [Line Items]
Long-term Debt, Principal Balance	[3]	$ 10,559	10,721
Stated Interest Rate	[3]	5.91%
Stated Maturity Date	[3]	Jun. 01, 2020
Solana Beach Towne Centre
Debt Instrument [Line Items]
Long-term Debt, Principal Balance	[3]	$ 35,196	35,737
Stated Interest Rate	[3]	5.91%
Stated Maturity Date	[3]	Jun. 01, 2020
City Center Bellevue
Debt Instrument [Line Items]
Long-term Debt, Principal Balance	[1]	$ 111,000	$ 111,000
Stated Interest Rate	[1]	3.98%
Stated Maturity Date	[1]	Nov. 01, 2022

[1] Interest only.

[2] Loan repaid in full, without premium or penalty, on March 30, 2018.

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