SEGMENT REPORTING - Net Real Estate and Secured Note Payable Balances (Details) - USD ($) $ in Thousands		Jun. 30, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Net Real Estate		$ 2,033,994	$ 2,076,707
Secured Notes Payable	[1]	205,413	279,889
American Assets Trust, L.P.
Segment Reporting Information [Line Items]
Net Real Estate		2,033,994	2,076,707
Secured notes payable, net | American Assets Trust, L.P.
Segment Reporting Information [Line Items]
Debt issuance costs, net		300	300
Total Retail
Segment Reporting Information [Line Items]
Net Real Estate		630,860	658,654
Secured Notes Payable	[1]	35,375	35,737
Total Office
Segment Reporting Information [Line Items]
Net Real Estate		806,336	813,121
Secured Notes Payable	[1]	170,038	170,408
Total Multifamily
Segment Reporting Information [Line Items]
Net Real Estate		418,173	424,044
Secured Notes Payable	[1]	0	73,744
Total Mixed-Use
Segment Reporting Information [Line Items]
Net Real Estate		178,625	180,888
Secured Notes Payable	[1]	$ 0	$ 0

[1] Excludes debt issuance costs of $0.3 million for each of the periods ending June 30, 2018 and December 31, 2017, respectively.