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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Equity [Abstract]
Net income	$ 11,941	$ 4,413	$ 27,184	$ 3,722
Less: Net income attributable to restricted shares	(92)	(216)	(185)	(144)
Less: Income from operations attributable to unitholders in the Operating Partnership	(2,933)	(1,125)	(6,988)	(959)
Net income attributable to common stockholders—basic	8,916	3,072	20,011	2,619
Income from operations attributable to American Assets Trust, Inc. common stockholders—basic	8,916	3,072	20,011	2,619
Plus: Income from operations attributable to unitholders in the Operating Partnership-diluted	2,933	1,125	6,988	959
Net income attributable to common stockholders-diluted	$ 11,849	$ 4,197	$ 26,999	$ 3,578
Weighted average common shares outstanding-basic (in shares)	50,135,978	46,939,449	48,578,872	46,937,645
Effect of dilutive securities-conversion of Operating Partnership units (in shares)	16,753,806	17,193,071	16,964,537	17,194,020
Weighted average common shares outstanding - diluted (in shares)	66,889,784	64,132,520	65,543,409	64,131,665
Earnings per common share, basic (in USD per share)	$ 0.18	$ 0.07	$ 0.41	$ 0.06
Earnings per common share, diluted (in USD per share)	$ 0.18	$ 0.07	$ 0.41	$ 0.06