Segment Reporting Net Real Estate and Secured Note Payable Balances for Each Segment (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Net Real Estate		$ 2,039,853	$ 2,076,707
Secured Notes Payable	[1]	182,765	279,889
Capital Expenditures and Leasing Commissions	[2]	64,347	52,423
Total Retail
Segment Reporting Information [Line Items]
Net Real Estate		628,734	658,654
Secured Notes Payable		35,008	35,737
Capital Expenditures and Leasing Commissions		14,219	10,412
Total Office
Segment Reporting Information [Line Items]
Net Real Estate		822,574	813,121
Secured Notes Payable		147,757	170,408
Capital Expenditures and Leasing Commissions		45,192	35,023
Total Multifamily
Segment Reporting Information [Line Items]
Net Real Estate		412,042	424,044
Secured Notes Payable		0	73,744
Capital Expenditures and Leasing Commissions		3,659	6,318
Total Mixed-Use
Segment Reporting Information [Line Items]
Net Real Estate		176,503	180,888
Secured Notes Payable		0	0
Capital Expenditures and Leasing Commissions		1,277	670
American Assets Trust, L.P.
Segment Reporting Information [Line Items]
Net Real Estate		2,039,853	2,076,707
Secured notes payable | American Assets Trust, L.P.
Segment Reporting Information [Line Items]
Debt Issuance Costs, Net		$ 193	$ 339

[1] Excludes unamortized debt issuance costs of $0.2 million and $0.3 million as of December 31, 2018 and 2017, respectively.

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