Partners Capital of American Assets Trust, L.P. (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Common Stock
Capital Unit [Line Items]
Conversion of operating partnership units (in shares)	209,011	787,060	17,372
American Assets Trust, L.P.
Capital Unit [Line Items]
Ownership percent by parent	78.80%
American Assets Trust, L.P.
Capital Unit [Line Items]
Noncontrolling common units (in shares)	16,181,537
American Assets Trust, L.P. | Common Stock
Capital Unit [Line Items]
Conversion of operating partnership units (in shares)	209,011	787,060	17,372
Non-Affiliated Investors | American Assets Trust, L.P.
Capital Unit [Line Items]
Percentage of ownership interests classified as noncontrolling	21.30%