EQUITY OF AMERICAN ASSETS TRUST, INC. - Computation of Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Equity [Abstract]
Net income	$ 15,484	$ 15,243
Less: Net income attributable to restricted shares	(104)	(93)
Less: Income from operations attributable to unitholders in the Operating Partnership	(3,312)	(4,055)
Net income attributable to common stockholders—basic	12,068	11,095
Income from operations attributable to American Assets Trust, Inc. common stockholders—basic	12,068	11,095
Plus: Income from operations attributable to unitholders in the Operating Partnership-diluted	3,312	4,055
Net income attributable to common stockholders-diluted	$ 15,380	$ 15,150
Weighted average common shares outstanding-basic (in shares)	59,723,072	47,004,465
Effect of dilutive securities-conversion of Operating Partnership units (in shares)	16,390,548	17,177,608
Weighted average common shares outstanding - diluted (in shares)	76,113,620	64,182,073
Earnings per common share, basic (in USD per share)	$ 0.20	$ 0.24
Earnings per common share, diluted (in USD per share)	$ 0.20	$ 0.24