PARTNERS CAPITAL OF AMERICAN ASSETS TRUST, L.P. (Details)	3 Months Ended				9 Months Ended
	Sep. 30, 2019 shares	Jun. 30, 2019 shares	Sep. 30, 2018 shares	Jun. 30, 2018 shares	Sep. 30, 2019 shares	Sep. 30, 2018 shares
Operating Partnership Units
Capital Unit [Line Items]
Antidilutive securities excluded from computation of EPS (in shares)	329,652		262,605		331,245	265,762
American Assets Trust, L.P.
Capital Unit [Line Items]
Noncontrolling common units (in shares)	16,390,548				16,390,548
Percentage of ownership interests classified as noncontrolling	21.60%				21.60%
American Assets Trust, L.P. | Operating Partnership Units
Capital Unit [Line Items]
Weighted average unvested shares outstanding (in shares)	329,652		262,605		331,245	265,762
Antidilutive securities excluded from computation of EPS (in shares)	329,652		262,605		331,245	265,762
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)		787,060		17,372
Common Shares | American Assets Trust, L.P.
Capital Unit [Line Items]
Conversion of operating partnership units (in shares)	0				787,060