EQUITY OF AMERICAN ASSETS TRUST, INC. - Computation of Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Equity [Abstract]
Net income from operations	$ 4,413	$ 7,588	$ 3,722	$ 17,896
Less: Net income attributable to restricted shares	(216)	(61)	(144)	(121)
Less: Income from operations attributable to unitholders in the Operating Partnership	(1,125)	(2,008)	(959)	(4,869)
Net income attributable to common stockholders—basic	3,072	5,519	2,619	12,906
Income from operations attributable to American Assets Trust, Inc. common stockholders—basic	3,072	5,519	2,619	12,906
Plus: Income from operations attributable to unitholders in the Operating Partnership	1,125	2,008	959	4,869
Plus: Income from operations attributable to unitholders in the Operating Partnership-diluted	(1,125)	(2,008)	(959)	(4,869)
Net income attributable to common stockholders-diluted	$ 4,197	$ 7,527	$ 3,578	$ 17,775
Weighted average common shares outstanding-basic (in shares)	46,939,449	46,871,377	46,937,645	46,524,510
Effect of dilutive securities-conversion of Operating Partnership units (in shares)	17,193,071	17,217,704	17,194,020	17,551,409
Weighted average common shares outstanding - diluted (in shares)	64,132,520	64,089,081	64,131,665	64,075,919
Earnings per common share, basic (in USD per share)	$ 0.07	$ 0.12	$ 0.06	$ 0.28
Earnings per common share, diluted (in USD per share)	$ 0.07	$ 0.12	$ 0.06	$ 0.28