PARTNERS' CAPITAL OF AMERICAN ASSETS TRUST, L.P. (Details)	3 Months Ended
	Mar. 31, 2021 shares	Mar. 31, 2020 shares
Operating Partnership Units
Capital Unit [Line Items]
Antidilutive securities excluded from computation of EPS (in shares)	489,775	345,153
American Assets Trust, L.P.
Capital Unit [Line Items]
Percentage of ownership interests classified as noncontrolling	21.30%
American Assets Trust, L.P.
Capital Unit [Line Items]
Noncontrolling common units (in shares)	16,181,537
American Assets Trust, L.P. | Operating Partnership Units
Capital Unit [Line Items]
Weighted average unvested shares outstanding (in shares)	489,775	345,153
Antidilutive securities excluded from computation of EPS (in shares)	489,775	345,153
Limited Partner | American Assets Trust, L.P.
Capital Unit [Line Items]
Common unit conversion ratio	1
Common Shares | American Assets Trust, L.P.
Capital Unit [Line Items]
Conversion of operating partnership units (in shares)	0