SEGMENT REPORTING - Net Real Estate and Secured Note Payable Balances (Details) - USD ($) $ in Thousands		Mar. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Net Real Estate		$ 2,054,982	$ 2,076,707
Secured Notes Payable	[1]	205,773	279,889
American Assets Trust, L.P.
Segment Reporting Information [Line Items]
Net Real Estate		2,054,982	2,076,707
Secured notes payable, net | American Assets Trust, L.P.
Segment Reporting Information [Line Items]
Debt issuance costs, net		300	339
Total Retail
Segment Reporting Information [Line Items]
Net Real Estate		644,573	658,654
Secured Notes Payable	[1]	35,552	35,737
Total Office
Segment Reporting Information [Line Items]
Net Real Estate		809,621	813,121
Secured Notes Payable	[1]	170,221	170,408
Total Multifamily
Segment Reporting Information [Line Items]
Net Real Estate		421,101	424,044
Secured Notes Payable	[1]	0	73,744
Total Mixed-Use
Segment Reporting Information [Line Items]
Net Real Estate		179,687	180,888
Secured Notes Payable	[1]	$ 0	$ 0

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