EQUITY OF AMERICAN ASSETS TRUST, INC. - Computation of Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Equity [Abstract]
Net income (loss)	$ 15,243	$ (691)
Less: Net (income) loss attributable to restricted shares	(93)	72
Less: (Income) loss from operations attributable to unitholders in the Operating Partnership	(4,055)	166
Net income (loss) attributable to common stockholders—basic	11,095	(453)
Income (loss) from operations attributable to American Assets Trust, Inc. common stockholders—basic	11,095	(453)
Plus: Income from operations attributable to unitholders in the Operating Partnership-diluted	4,055	0
Net income attributable to common stockholders-diluted	$ 15,150	$ (453)
Weighted average common shares outstanding-basic (in shares)	47,004,465	46,935,820
Effect of dilutive securities-conversion of Operating Partnership units (in shares)	17,177,608	0
Weighted average common shares outstanding - diluted (in shares)	64,182,073	46,935,820
Earnings per common share, basic (in USD per share)	$ 0.24	$ (0.01)
Earnings per common share, diluted (in USD per share)	$ 0.24	$ (0.01)