Debt Summary of Total Secured Notes Payable Outstanding (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Debt issuance costs, net	$ 0	$ (1,256)
Notes payable, total	1,311,000
Debt issuance costs, accumulated amortization	0	814
Secured notes payable | American Assets Trust, L.P.
Debt Instrument [Line Items]
Long-term Debt, Principal Balance	111,000	162,003
Debt issuance costs, net	(77)	(124)
Notes payable, total	$ 110,923	161,879
Number of year amortization schedule	30 years
Secured notes payable | American Assets Trust, L.P. | Torrey Reserve-VCI, VCII, VCIII
Debt Instrument [Line Items]
Long-term Debt, Principal Balance	$ 0	6,498
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]
Long-term Debt, Principal Balance	$ 0	10,270
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]
Long-term Debt, Principal Balance	$ 0	34,235
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]
Long-term Debt, Principal Balance	$ 111,000	111,000
Stated Interest Rate	3.98%
Stated Maturity Date	Nov. 01, 2022
Unsecured debt
Debt Instrument [Line Items]
Debt issuance costs, accumulated amortization	$ 345	449
Unsecured debt | American Assets Trust, L.P.
Debt Instrument [Line Items]
Long-term Debt, Principal Balance	1,200,000	1,200,000
Debt issuance costs, net	(3,323)	(4,220)
Debt issuance costs, accumulated amortization	$ 8,856	$ 7,835