EQUITY OF AMERICAN ASSETS TRUST, INC. - Computation of Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Equity [Abstract]
Net (loss) income from operations	$ (691)	$ 10,308
Less: Net loss (income) attributable to restricted shares	72	(60)
Less: Loss (income) from operations attributable to unitholders in the Operating Partnership	166	(2,861)
Net (loss) income attributable to common stockholders—basic	(453)	7,387
(Loss) income from operations attributable to American Assets Trust, Inc. common stockholders—basic	(453)	7,387
Plus: Income from operations attributable to unitholders in the Operating Partnership	(166)	2,861
Plus: Income from operations attributable to unitholders in the Operating Partnership-diluted	0	(2,861)
(Loss) income from continuing operations attributable to common stockholders - diluted	(453)	10,248
Net income attributable to common stockholders-diluted	$ (453)	$ 10,248
Weighted average common shares outstanding-basic (in shares)	46,935,820	46,173,788
Effect of dilutive securities-conversion of Operating Partnership units (in shares)	0	17,888,822
Weighted average common shares outstanding - diluted (in shares)	46,935,820	64,062,610
Earnings per common share, basic (in USD per share)	$ (0.01)	$ 0.16
Earnings per common share, diluted (in USD per share)	$ (0.01)	$ 0.16