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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Equity [Abstract]
Net income from operations	$ 14,271	$ 12,505	$ 17,993	$ 30,401
Less: Net income attributable to restricted shares	(71)	(60)	(215)	(181)
Less: Income from operations attributable to unitholders in the Operating Partnership	(3,806)	(3,351)	(4,765)	(8,220)
Net income attributable to common stockholders—basic	10,394	9,094	13,013	22,000
Income from operations attributable to American Assets Trust, Inc. common stockholders—basic	10,394	9,094	13,013	22,000
Plus: Income from operations attributable to unitholders in the Operating Partnership-diluted	3,806	3,351	4,765	8,220
Net income attributable to common stockholders-diluted	$ 14,200	$ 12,445	$ 17,778	$ 30,220
Weighted average common shares outstanding-basic (in shares)	46,959,752	46,898,086	46,945,095	46,650,403
Effect of dilutive securities-conversion of Operating Partnership units (in shares)	17,177,608	17,194,980	17,188,489	17,431,294
Weighted average common shares outstanding - diluted (in shares)	64,137,360	64,093,066	64,133,584	64,081,697
Earnings per common share, basic (in USD per share)	$ 0.22	$ 0.19	$ 0.28	$ 0.47
Earnings per common share, diluted (in USD per share)	$ 0.22	$ 0.19	$ 0.28	$ 0.47