SEGMENT REPORTING - Net Real Estate and Secured Note Payable Balances (Details) - USD ($) $ in Thousands		Sep. 30, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Net Real Estate		$ 1,833,520	$ 1,834,862
Secured Notes Payable	[1]	470,490	584,002
American Assets Trust, L.P.
Segment Reporting Information [Line Items]
Net Real Estate		1,833,520	1,834,862
Secured notes payable, net | American Assets Trust, L.P.
Segment Reporting Information [Line Items]
Unamortized fair value adjustment and debt issuance costs		2,600	5,000
Total Retail
Segment Reporting Information [Line Items]
Net Real Estate		632,964	638,893
Secured Notes Payable	[1]	59,591	60,065
Total Office
Segment Reporting Information [Line Items]
Net Real Estate		809,730	796,773
Secured Notes Payable	[1]	206,845	292,183
Total Multifamily
Segment Reporting Information [Line Items]
Net Real Estate		204,316	208,730
Secured Notes Payable	[1]	73,744	101,444
Total Mixed-Use
Segment Reporting Information [Line Items]
Net Real Estate		186,510	190,466
Secured Notes Payable	[1]	$ 130,310	$ 130,310

[1] Excludes unamortized fair market value adjustments and debt issuance costs of $2.6 million and $5.0 million as of September 30, 2016 and December 31, 2015, respectively.