EQUITY OF AMERICAN ASSETS TRUST, INC. - Computation of Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Equity [Abstract]
Net income	$ 11,487	$ 9,826	$ 13,220	$ 25,310
Less: Net income attributable to restricted shares	(135)	(69)	(272)	(173)
Less: Income from operations attributable to unitholders in the Operating Partnership	(2,411)	(2,101)	(2,750)	(5,413)
Net income attributable to American Assets Trust, Inc. stockholders	8,941	7,656	10,198	19,724
Income from operations attributable to American Assets Trust, Inc. common stockholders—basic	8,941	7,656	10,198	19,724
Plus: Income from operations attributable to unitholders in the Operating Partnership-diluted	2,411	2,101	2,750	5,413
Net income attributable to common stockholders-diluted	$ 11,352	$ 9,757	$ 12,948	$ 25,137
Weighted average common shares outstanding-basic (in shares)	59,985,787	59,724,139	59,985,065	59,723,605
Effect of dilutive securities-conversion of Operating Partnership units (in shares)	16,181,537	16,390,548	16,181,537	16,390,548
Weighted average common shares outstanding - diluted (in shares)	76,167,324	76,114,687	76,166,602	76,114,153
Earnings per common share, basic (in USD per share)	$ 0.15	$ 0.13	$ 0.17	$ 0.33
Earnings per common share, diluted (in USD per share)	$ 0.15	$ 0.13	$ 0.17	$ 0.33
American Assets Trust, L.P.
Equity [Abstract]
Less: Net income attributable to restricted shares	$ (135)	$ (69)	$ (272)	$ (173)
Net income attributable to American Assets Trust, Inc. stockholders	$ 11,352	$ 9,757	$ 12,948	$ 25,137
Weighted average common shares outstanding-basic (in shares)	76,167,324	76,114,687	76,166,602	76,114,153
Weighted average common shares outstanding - diluted (in shares)	76,167,324	76,114,687	76,166,602	76,114,153
Earnings per common share, basic (in USD per share)	$ 0.15	$ 0.13	$ 0.17	$ 0.33
Earnings per common share, diluted (in USD per share)	$ 0.15	$ 0.13	$ 0.17	$ 0.33