Quarterly Financial Information (Unaudited) Selected Quarterly Information (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Quarterly Financial Information Disclosure [Abstract]
Total revenue	$ 64,645	$ 65,318	$ 62,914	$ 62,180	$ 63,120	$ 60,766	$ 56,131	$ 55,449	$ 255,057	$ 235,466	$ 202,785
Operating income (loss)	20,407	21,441	19,373	19,880	20,247	18,206	16,641	16,812	81,101	71,906	56,343
Income (loss) from continuing operations					4,822	3,968	2,396	2,763	22,594	13,949	13,671
Results from discontinued operations					36,999	317	228	108	0	37,652	5,653
Net income	6,907	6,258	4,564	4,865	41,821	4,285	2,624	2,871	22,594	51,601	19,324
Net income attributable to restricted shares	(139)	(132)	(133)	(132)	(133)	(133)	(131)	(132)	(536)	(529)	(482)
Net income attributable to unitholders in the Operating Partnership	(2,086)	(1,903)	(1,354)	(1,495)	(13,111)	(1,335)	(804)	(883)	(6,838)	(16,133)	(1,388)
Net income (loss) attributable to American Assets Trust, Inc. stockholders	$ 4,682	$ 4,223	$ 3,077	$ 3,238	$ 28,577	$ 2,817	$ 1,689	$ 1,856	$ 15,220	$ 34,939	$ 2,917
Net income from continuing operations attributable to common stockholders-basic and diluted	$ 0.11	$ 0.11	$ 0.08	$ 0.08	$ 0.08	$ 0.07	$ 0.04	$ 0.05
Net income from discontinued operations attributable to common stockholders-basic and diluted					$ 0.65	$ 0.01	$ 0.00	$ 0.00
Net income attributable to common stockholders-basic and diluted	$ 0.11	$ 0.11	$ 0.08	$ 0.08	$ 0.73	$ 0.08	$ 0.04	$ 0.05