Equity Computation of Basic and Diluted EPS (Details) (USD $) In Thousands, except 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
NUMERATOR
Income from continuing operations					$ 4,822	$ 3,968	$ 2,396	$ 2,763	$ 22,594	$ 13,949	$ 13,671
Less: Net income attributable to restricted shares	(139)	(132)	(133)	(132)	(133)	(133)	(131)	(132)	(536)	(529)	(482)
Plus: Loss from continuing operations attributable to Predecessor's noncontrolling interests in consolidated real estate entities									0	0	2,455
Less: Income from continuing operations attributable to Predecessor's controlled owners' equity									0	0	(16,962)
Plus: (Income) loss from continuing operations attributable to unitholders in the Operating Partnership									(6,838)	(4,239)	425
Income (loss) from continuing operations attributable to American Assets Trust, Inc. common stockholders-basic									15,220	9,181	(893)
Plus: Results from discontinued operations attributable to American Assets Trust, Inc. common stockholders									0	25,758	3,810
NET INCOME 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
Income (loss) from continuing operations attributable to American Assets Trust, Inc. common stockholders—basic									15,220	9,181	(893)
Less: Income (loss) from continuing operations attributable to unitholders in the Operating Partnership									6,838	4,239	(425)
Income (loss) from continuing operations attributable to common stockholders-diluted									22,058	13,420	(1,318)
Plus: Results from discontinued operations attributable to American Assets Trust, Inc. common stockholders									0	25,758	3,810
Plus: Results from discontinued operations attributable to unitholders in the Operating Partnership									0	11,894	1,813
Net income attributable to common stockholders-diluted									$ 22,058	$ 51,072	$ 4,305
DENOMINATOR
Weighted average common shares outstanding-basic									39,539,457	38,736,113	36,748,806
Effect of dilutive securities-conversion of Operating Partnership units									17,976,353	18,317,796	17,471,001
Weighted average common shares outstanding - diluted									57,515,810	57,053,909	54,219,807
Earnings (loss) per common share-basic
Continuing operations									$ 0.38	$ 0.24	$ (0.02)
Discontinued operations									$ 0.00	$ 0.66	$ 0.10
Basic net income attributable to common stockholders per share									$ 0.38	$ 0.90	$ 0.08
Earnings (loss) per common share-diluted
Continuing operations									$ 0.38	$ 0.24	$ (0.02)
Discontinued operations									$ 0.00	$ 0.66	$ 0.10
Diluted net income attributable to common stockholders per share									$ 0.38	$ 0.90	$ 0.08