Selected Quarterly Information (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Quarterly Financial Information [Line Items]
Total revenue	$ 63,120	$ 60,766	$ 56,131	$ 55,449	$ 53,838	$ 54,370	$ 49,318	$ 45,259	$ 235,466	$ 202,785	$ 117,748
Operating income (loss)	20,247	18,206	16,641	16,812	14,182	14,427	12,969	14,765	71,906	56,343	42,422
Income (loss) from continuing operations	4,822	3,968	2,396	2,763	560	(59)	(172)	13,342	13,949	13,671	1,622
Results from discontinued operations	36,999	317	228	108	95	4,677	627	254	37,652	5,653	552
Net income	41,821	4,285	2,624	2,871	655	4,618	455	13,596	51,601	19,324	2,174
Net income attributable to restricted shares	(133)	(133)	(131)	(132)	(132)	(132)	(132)	(86)	(529)	(482)
Net loss attributable to Predecessor's noncontrolling interests in consolidated real estate entities								2,458		(2,458)	(2,205)
Net income attributable to Predecessor's controlled owners' equity								(16,995)		(16,995)	(4,379)
Net (income) loss attributable to unitholders in the Operating Partnership	(13,111)	(1,335)	(804)	(883)	(179)	(1,434)	(104)	329	16,133	1,388
Net income (loss) attributable to American Assets Trust, Inc. stockholders	$ 28,577	$ 2,817	$ 1,689	$ 1,856	$ 344	$ 3,052	$ 219	$ (698)	$ 34,939	$ 2,917
Net income from continuing operations attributable to common stockholders-basic and diluted	$ 0.08	$ 0.07	$ 0.04	$ 0.05	$ 0.01			$ (0.03)
Net income from discontinued operations attributable to common stockholders-basic and diluted	$ 0.65	$ 0.01				$ 0.08	$ 0.01	$ 0.01
Net income attributable to common stockholders-basic and diluted	$ 0.73	$ 0.08	$ 0.04	$ 0.05	$ 0.01	$ 0.08	$ 0.01	$ (0.02)