EQUITY OF AMERICAN ASSETS TRUST, INC. - Computation of Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Equity [Abstract]
Net income from operations	$ 12,505	$ 11,858	$ 30,401	$ 33,229
Less: Net income attributable to restricted shares	(60)	(42)	(181)	(128)
Less: Income from operations attributable to unitholders in the Operating Partnership	(3,351)	(3,342)	(8,220)	(9,377)
Net income attributable to common stockholders—basic	9,094	8,474	22,000	23,724
Income from operations attributable to American Assets Trust, Inc. common stockholders—basic	9,094	8,474	22,000	23,724
Plus: Income from operations attributable to unitholders in the Operating Partnership	3,351	3,342	8,220	9,377
Net income attributable to common stockholders-diluted	$ 12,445	$ 11,816	$ 30,220	$ 33,101
Weighted average common shares outstanding-basic (in shares)	46,898,086	45,377,719	46,650,403	45,282,643
Effect of dilutive securities-conversion of Operating Partnership units (in shares)	17,194,980	17,894,983	17,431,294	17,897,994
Weighted average common shares outstanding - diluted (in shares)	64,093,066	63,272,702	64,081,697	63,180,637
Earnings per common share, basic (in USD per share)	$ 0.19	$ 0.19	$ 0.47	$ 0.52
Earnings per common share, diluted (in USD per share)	$ 0.19	$ 0.19	$ 0.47	$ 0.52