SEGMENT REPORTING - Net Real Estate and Secured Note Payable Balances (Details) - USD ($) $ in Thousands		Mar. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Net Real Estate		$ 1,837,000	$ 1,834,862
Secured Notes Payable	[1]	499,063	584,002
American Assets Trust, L.P.
Segment Reporting Information [Line Items]
Net Real Estate		1,837,000	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		4,180	5,002
Total Retail
Segment Reporting Information [Line Items]
Net Real Estate		639,793	638,893
Secured Notes Payable	[1]	59,905	60,065
Total Office
Segment Reporting Information [Line Items]
Net Real Estate		800,358	796,773
Secured Notes Payable	[1]	207,404	292,183
Total Multifamily
Segment Reporting Information [Line Items]
Net Real Estate		207,725	208,730
Secured Notes Payable	[1]	101,444	101,444
Total Mixed-Use
Segment Reporting Information [Line Items]
Net Real Estate		189,124	190,466
Secured Notes Payable	[1]	$ 130,310	$ 130,310

[1] Excludes unamortized fair market value adjustments and debt issuance costs of $4.2 million and $5.0 million as of March 31, 2016 and December 31, 2015, respectively.