SEGMENT REPORTING - Net Real Estate and Secured Note Payable Balances (Details) - USD ($) $ in Thousands		Jun. 30, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Net Real Estate		$ 2,486,060	$ 2,492,734
Secured Notes Payable	[1]	111,000	111,000
Debt issuance costs, net of accumulated amortization of $1,425 and $0, respectively		645	0
American Assets Trust, L.P.
Segment Reporting Information [Line Items]
Net Real Estate		2,486,060	2,492,734
Secured notes payable, net | American Assets Trust, L.P.
Segment Reporting Information [Line Items]
Debt issuance costs, net of accumulated amortization of $1,425 and $0, respectively		56	77
Office
Segment Reporting Information [Line Items]
Net Real Estate		1,326,624	1,317,107
Secured Notes Payable	[1]	111,000	111,000
Retail
Segment Reporting Information [Line Items]
Net Real Estate		599,244	607,918
Multifamily
Segment Reporting Information [Line Items]
Net Real Estate		384,733	389,804
Mixed-use
Segment Reporting Information [Line Items]
Net Real Estate		$ 175,459	$ 177,905

[1] Excludes debt issuance costs of $0.1 million and $0.1 million for each of the periods ended June 30, 2021 and December 31, 2020, respectively.