Segment Reporting Net Real Estate and Secured Note Payable Balances for Each Segment (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Net real estate		$ 2,523,475	$ 2,039,853
Secured Notes Payable	[1]	162,003	182,765
Capital Expenditures and Leasing Commissions	[2]	99,594	64,347
Debt issuance costs, net of accumulated amortization of $814 and $0, respectively		1,256	0
Total Retail
Segment Reporting Information [Line Items]
Net real estate		624,912	628,734
Secured Notes Payable		34,235	35,008
Capital Expenditures and Leasing Commissions		22,844	14,219
Total Office
Segment Reporting Information [Line Items]
Net real estate		1,317,854	822,574
Secured Notes Payable		127,768	147,757
Capital Expenditures and Leasing Commissions		64,549	45,192
Total Multifamily
Segment Reporting Information [Line Items]
Net real estate		401,152	412,042
Capital Expenditures and Leasing Commissions		3,711	3,659
Total Mixed-Use
Segment Reporting Information [Line Items]
Net real estate		179,557	176,503
Capital Expenditures and Leasing Commissions		8,490	1,277
American Assets Trust, L.P.
Segment Reporting Information [Line Items]
Net real estate		2,523,475	2,039,853
Secured notes payable | American Assets Trust, L.P.
Segment Reporting Information [Line Items]
Debt issuance costs, net of accumulated amortization of $814 and $0, respectively		$ 124	$ 193

[1] Excludes unamortized debt issuance costs of $0.1 million and $0.2 million as of December 31, 2019 and 2018, respectively.

[2] Capital expenditures represent cash paid for capital expenditures during the year and includes leasing commissions paid.