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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Equity [Abstract]
Net income	$ 16,519	$ 14,271	$ 43,703	$ 17,993
Less: Net income attributable to restricted shares	(92)	(71)	(277)	(215)
Less: Income from operations attributable to unitholders in the Operating Partnership	(3,565)	(3,806)	(10,553)	(4,765)
Net income attributable to common stockholders—basic	12,862	10,394	32,873	13,013
Income from operations attributable to American Assets Trust, Inc. common stockholders—basic	12,862	10,394	32,873	13,013
Plus: Income from operations attributable to unitholders in the Operating Partnership-diluted	3,565	3,806	10,553	4,765
Net income attributable to common stockholders-diluted	$ 16,427	$ 14,200	$ 43,426	$ 17,778
Weighted average common shares outstanding-basic (in shares)	59,441,887	46,959,752	52,239,668	46,945,095
Effect of dilutive securities-conversion of Operating Partnership units (in shares)	16,390,548	17,177,608	16,771,104	17,188,489
Weighted average common shares outstanding - diluted (in shares)	75,832,435	64,137,360	69,010,772	64,133,584
Earnings per common share, basic (in USD per share)	$ 0.22	$ 0.22	$ 0.63	$ 0.28
Earnings per common share, diluted (in USD per share)	$ 0.22	$ 0.22	$ 0.63	$ 0.28