Segment Reporting Net Real Estate and Secured Note Payable Balances for Each Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Net real estate	$ 2,492,734	$ 2,523,475
Secured Notes Payable	111,000	162,003
Capital Expenditures and Leasing Commissions	69,077	99,594
Debt issuance costs, net of accumulated amortization of $0 and $814, respectively	0	1,256
Total Retail
Segment Reporting Information [Line Items]
Net real estate	607,918	624,912
Secured Notes Payable	0	34,235
Capital Expenditures and Leasing Commissions	8,596	22,844
Total Office
Segment Reporting Information [Line Items]
Net real estate	1,317,107	1,317,854
Secured Notes Payable	111,000	127,768
Capital Expenditures and Leasing Commissions	52,882	64,549
Total Multifamily
Segment Reporting Information [Line Items]
Net real estate	389,804	401,152
Capital Expenditures and Leasing Commissions	3,897	3,711
Total Mixed-Use
Segment Reporting Information [Line Items]
Net real estate	177,905	179,557
Capital Expenditures and Leasing Commissions	3,702	8,490
American Assets Trust, L.P.
Segment Reporting Information [Line Items]
Net real estate	2,492,734	2,523,475
Secured notes payable | American Assets Trust, L.P.
Segment Reporting Information [Line Items]
Debt issuance costs, net of accumulated amortization of $0 and $814, respectively	$ 77	$ 124