Equity (Details 2) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
NUMERATOR
Income from continuing operations	$ 4,498	$ 310	$ 9,993	$ 13,569
Less: Net income attributable to restricted shares	(133)	(132)	(396)	(350)
Plus: Loss from continuing operations attributable to Predecessor's noncontrolling interests in consolidated real estate entities				2,454
Less: Income from continuing operations attributable to Predecessor's controlled owners' equity				(17,009)
Less: (Income) loss from continuing operations attributable to unitholders in the Operating Partnership	(1,403)	(57)	(3,090)	427
Income (loss) from continuing operations attributable to American Assets Trust, Inc. common stockholders-basic	2,962	121	6,507	(909)
Plus: Results from discontinued operations attributable to American Assets Trust, Inc. common stockholders	(145)	2,931	(145)	3,482
NET INCOME ATTRIBUTABLE TO AMERICAN ASSETS TRUST. INC. STOCKHOLDERS	2,817	3,052	6,362	2,573
Income (loss) from continuing operations attributable to American Assets Trust, Inc. common stockholders-basic	2,962	121	6,507	(909)
Plus: Income (loss) from continuing operations attributable to unitholders in the Operating Partnership	1,403	57	3,090	(427)
Income (loss) from continuing operations attributable to common stockholders-diluted	4,365	178	9,597	(1,336)
Plus: Results from discontinued operations attributable to unitholders in the Operating Partnership	(68)	1,377	(68)	1,636
Net income attributable to common stockholders-diluted	$ 4,152	$ 4,486	$ 9,384	$ 3,782
DENOMINATOR
Weighted average common shares outstanding-basic	38,673,617	38,655,084	38,663,352	36,106,397
Effect of dilutive securities-conversion of Operating Partnership units	18,380,808	18,396,089	18,391,073	17,159,251
Weighted average common shares outstanding - diluted	57,054,425	57,051,173	57,054,425	53,265,648
EARNINGS (LOSS) PER COMMON SHARE - BASIC
Continuing operations	$ 0.08		$ 0.17	$ (0.03)
Discontinued operations		$ 0.08		$ 0.10
Earnings per share-basic, Total	$ 0.08	$ 0.08	$ 0.17	$ 0.07
EARNINGS (LOSS) PER COMMON SHARE - DILUTED
Continuing operations	$ 0.08		$ 0.17	$ (0.03)
Discontinued operations		$ 0.08		$ 0.10
Earnings per share-diluted, Total	$ 0.08	$ 0.08	$ 0.17	$ 0.07