PARTNERS' CAPITAL OF AMERICAN ASSETS TRUST, L.P. (Details)	3 Months Ended			9 Months Ended
	Sep. 30, 2020 shares	Sep. 30, 2019 shares	Jun. 30, 2019 shares	Sep. 30, 2020 shares	Sep. 30, 2019 shares
American Assets Trust, L.P.
Capital Unit [Line Items]
Percentage of ownership interests classified as noncontrolling	21.30%			21.30%
Operating Partnership Units
Capital Unit [Line Items]
Antidilutive securities excluded from computation of EPS (in shares)	346,434	329,652		345,613	331,245
American Assets Trust, L.P.
Capital Unit [Line Items]
Noncontrolling common units (in shares)	16,181,537			16,181,537
American Assets Trust, L.P. | Operating Partnership Units
Capital Unit [Line Items]
Weighted average unvested shares outstanding (in shares)	346,434	329,652		345,613	331,245
Antidilutive securities excluded from computation of EPS (in shares)	346,434	329,652		345,613	331,245
Limited Partner | American Assets Trust, L.P.
Capital Unit [Line Items]
Common unit conversion ratio				1
Common Shares
Capital Unit [Line Items]
Conversion of operating partnership units (in shares)	209,011		787,060
Common Shares | American Assets Trust, L.P.
Capital Unit [Line Items]
Conversion of operating partnership units (in shares)				209,011