Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2018	Dec. 31, 2017
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 (in shares)	47,222,121	47,204,588
Common stock, shares issued (in shares)	47,222,121	47,204,588
American Assets Trust, L.P.
Limited partners' capital, units issued (in shares)	17,177,608	17,194,980
Limited partners' capital, units outstanding (in shares)	17,177,608	17,194,980
General partners' capital, units issued (in shares)	47,222,121	47,204,588
General partners' capital, units outstanding (in shares)	47,222,121	47,204,588