Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2021	Dec. 31, 2020
Common stock, par value (in USD per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	490,000,000	490,000,000
Common stock, shares outstanding (shares)	60,472,065	60,476,292
Common stock, shares issued (in shares)	60,472,065	60,476,292
American Assets Trust, L.P.
Limited partners' capital, units outstanding (in shares)	16,181,537	16,181,537
Limited partners' capital, units issued (in shares)	16,181,537	16,181,537
General partners' capital, units issued (in shares)	60,472,065	60,476,292
General partners' capital, units outstanding (in shares)	60,472,065	60,476,292