Debt Summary of Total Secured Notes Payable Outstanding (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Notes payable, total	$ 1,232,765
Secured notes payable \| American Assets Trust, L.P.
Debt Instrument [Line Items]
Secured notes payable, Principal Balance	182,765	$ 279,889
Debt issuance costs, net	(193)	(339)
Notes payable, total	$ 182,572	279,550
Number of year amortization schedule	30 years
Debt issuance costs, accumulated amortization	$ 671	1,191
Secured notes payable \| American Assets Trust, L.P. \| Loma Palisades
Debt Instrument [Line Items]
Secured notes payable, Principal Balance	$ 0	73,744
Stated Interest Rate	6.09%
Stated Maturity Date	Jul. 01, 2018
Secured notes payable \| American Assets Trust, L.P. \| One Beach Street
Debt Instrument [Line Items]
Secured notes payable, Principal Balance	$ 0	21,900
Stated Interest Rate	3.94%
Stated Maturity Date	Apr. 01, 2019
Secured notes payable \| American Assets Trust, L.P. \| Torrey Reserve - North Court
Debt Instrument [Line Items]
Secured notes payable, Principal Balance	$ 19,620	20,023
Stated Interest Rate	7.22%
Stated Maturity Date	Jun. 01, 2019
Secured notes payable \| American Assets Trust, L.P. \| Torrey Reserve-VCI, VCII, VCIII
Debt Instrument [Line Items]
Secured notes payable, Principal Balance	$ 6,635	6,764
Stated Interest Rate	6.36%
Stated Maturity Date	Jun. 01, 2020
Secured notes payable \| American Assets Trust, L.P. \| Solana Beach Corporate Centre I-II
Debt Instrument [Line Items]
Secured notes payable, Principal Balance	$ 10,502	10,721
Stated Interest Rate	5.91%
Stated Maturity Date	Jun. 01, 2020
Secured notes payable \| American Assets Trust, L.P. \| Solana Beach Towne Centre
Debt Instrument [Line Items]
Secured notes payable, Principal Balance	$ 35,008	35,737
Stated Interest Rate	5.91%
Stated Maturity Date	Jun. 01, 2020
Secured notes payable \| American Assets Trust, L.P. \| City Center Bellevue
Debt Instrument [Line Items]
Secured notes payable, Principal Balance	$ 111,000	$ 111,000
Stated Interest Rate	3.98%
Stated Maturity Date	Nov. 01, 2022

Amount of accumulated amortization of debt issuance costs.

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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