Partners Capital of American Assets Trust, L.P. (Details) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Capital Unit [Line Items]
Ownership percent by parent	73.20%
Common Stock
Capital Unit [Line Items]
Conversion of operating partnership units (in shares)	17,372	693,842	10,694
American Assets Trust, L.P.
Capital Unit [Line Items]
Noncontrolling common units (in shares)	17,177,608
Percentage of ownership interests classified as noncontrolling	26.80%
American Assets Trust, L.P. | Common Stock
Capital Unit [Line Items]
Conversion of operating partnership units (in shares)	17,372	693,842	10,694