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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Equity [Abstract]
Net income	$ 6,490	$ 16,519	$ 31,800	$ 43,703
Less: Net income attributable to restricted shares	(87)	(92)	(260)	(277)
Less: Income from operations attributable to unitholders in the Operating Partnership	(1,365)	(3,565)	(6,778)	(10,553)
Net income attributable to common stockholders—basic	5,038	12,862	24,762	32,873
Income from operations attributable to American Assets Trust, Inc. common stockholders—basic	5,038	12,862	24,762	32,873
Plus: Income from operations attributable to unitholders in the Operating Partnership-diluted	1,365	3,565	6,778	10,553
Net income attributable to common stockholders-diluted	$ 6,403	$ 16,427	$ 31,540	$ 43,426
Weighted average common shares outstanding-basic (in shares)	59,825,174	59,441,887	59,757,709	52,239,668
Effect of dilutive securities-conversion of Operating Partnership units (in shares)	16,292,858	16,390,548	16,357,747	16,771,104
Weighted average common shares outstanding - diluted (in shares)	76,118,032	75,832,435	76,115,456	69,010,772
Earnings per common share, basic (in USD per share)	$ 0.08	$ 0.22	$ 0.41	$ 0.63
Earnings per common share, diluted (in USD per share)	$ 0.08	$ 0.22	$ 0.41	$ 0.63