Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2019	Dec. 31, 2018
Common Shares
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)	59,956,972	47,335,409
Common stock, shares issued (in shares)	59,956,972	47,335,409
American Assets Trust, L.P.
Limited partners' capital, units issued (in shares)	16,390,548	17,177,608
Limited partners' capital, units outstanding (in shares)	16,390,548	17,177,608
General partners' capital, units issued (in shares)	59,956,972	47,335,409
General partners' capital, units outstanding (in shares)	59,956,972	47,335,409