EQUITY Computation of Basic and Diluted EPS (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Equity [Abstract]
Income from continuing operations	$ 6,258	$ 3,966	$ 15,687	$ 9,127
Less: Net income attributable to restricted shares	(132)	(133)	(397)	(396)
Less: Income from continuing operations attributable to unitholders in the Operating Partnership	(1,903)	(1,234)	(4,752)	(2,813)
Income from continuing operations attributable to American Assets Trust, Inc. common stockholders-basic	4,223	2,599	10,538	5,918
Plus: Results from discontinued operations attributable to American Assets Trust, Inc. common stockholders	0	218	0	444
Income from continuing operations attributable to American Assets Trust, Inc. common stockholders-basic	4,223	2,817	10,538	6,362
Income from continuing operations attributable to common stockholders-diluted	6,126	3,833	15,290	8,731
Plus: Results from discontinued operations attributable to unitholders in the Operating Partnership	0	101	0	209
Net income attributable to common stockholders-diluted	$ 6,126	$ 4,152	$ 15,290	$ 9,384
Weighted average common shares outstanding-basic	39,816,753	38,673,617	39,439,488	38,663,352
Effect of dilutive securities-conversion of Operating Partnership units	17,960,914	18,380,808	17,984,471	18,391,073
Weighted average common shares outstanding - diluted	57,777,667	57,054,425	57,423,959	57,054,425
Continuing operations	$ 0.11	$ 0.07	$ 0.27	$ 0.16
Discontinued operations	$ 0.00	$ 0.01	$ 0.00	$ 0.01
Basic net income attributable to common stockholders per share	$ 0.11	$ 0.08	$ 0.27	$ 0.17
Continuing operations	$ 0.11	$ 0.07	$ 0.27	$ 0.16
Discontinued operations	$ 0.00	$ 0.01	$ 0.00	$ 0.01
Diluted net income attributable to common stockholders per share	$ 0.11	$ 0.08	$ 0.27	$ 0.17