SEGMENT REPORTING - Net Real Estate and Secured Note Payable Balances (Details) - USD ($) $ in Thousands		Mar. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Net Real Estate		$ 2,521,569	$ 2,523,475
Secured Notes Payable	[1]	111,000	162,003
Debt issuance costs, net of accumulated amortization of $916 and $814, respectively		1,154	1,256
American Assets Trust, L.P.
Segment Reporting Information [Line Items]
Net Real Estate		2,521,569	2,523,475
Secured notes payable, net | American Assets Trust, L.P.
Segment Reporting Information [Line Items]
Debt issuance costs, net of accumulated amortization of $916 and $814, respectively		108	124
Retail
Segment Reporting Information [Line Items]
Net Real Estate		620,598	624,912
Secured Notes Payable	[1]	0	34,235
Office
Segment Reporting Information [Line Items]
Net Real Estate		1,323,207	1,317,854
Secured Notes Payable	[1]	111,000	127,768
Multifamily
Segment Reporting Information [Line Items]
Net Real Estate		398,459	401,152
Mixed-use
Segment Reporting Information [Line Items]
Net Real Estate		$ 179,305	$ 179,557

[1] Excludes debt issuance costs of $0.1 million and $0.1 million for each of the periods ended March 31, 2020 and December 31, 2019, respectively.