EQUITY OF AMERICAN ASSETS TRUST, INC. - Computation of Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Equity [Abstract]
Net income	$ 1,733	$ 15,484
Less: Net income attributable to restricted shares	(137)	(104)
Less: Income from operations attributable to unitholders in the Operating Partnership	(339)	(3,312)
Net income attributable to common stockholders—basic	1,257	12,068
Income from operations attributable to American Assets Trust, Inc. common stockholders—basic	1,257	12,068
Plus: Income from operations attributable to unitholders in the Operating Partnership-diluted	339	3,312
Net income attributable to common stockholders-diluted	$ 1,596	$ 15,380
Weighted average common shares outstanding-basic (in shares)	59,984,335	59,723,072
Effect of dilutive securities-conversion of Operating Partnership units (in shares)	16,181,537	16,390,548
Weighted average common shares outstanding - diluted (in shares)	76,165,872	76,113,620
Earnings per common share, basic (in USD per share)	$ 0.02	$ 0.20
Earnings per common share, diluted (in USD per share)	$ 0.02	$ 0.20