Equity of American Assets Trust, Inc. Computation of Basic and Diluted EPS (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
NUMERATOR
Income from continuing operations									$ 31,145	$ 22,594	$ 13,949
Less: Net income attributable to restricted shares	(115)	(95)	(94)	(70)	(139)	(132)	(133)	(132)	(374)	(536)	(529)
Less: Income from continuing operations attributable to unitholders in the Operating Partnership									(9,015)	(6,838)	(4,239)
Income (loss) from continuing operations attributable to American Assets Trust, Inc. common stockholders-basic									21,756	15,220	9,181
Plus: Results from discontinued operations attributable to American Assets Trust, Inc. common stockholders									0	0	25,757
NET INCOME ATTRIBUTABLE TO AMERICAN ASSETS TRUST, INC. STOCKHOLDERS	7,024	6,417	3,713	4,602	4,682	4,223	3,077	3,238	21,756	15,220	34,938
Income from continuing operations attributable to American Assets Trust, Inc. common stockholders—basic									21,756	15,220	9,181
Plus: Income from continuing operations attributable to unitholders in the Operating Partnership									9,015	6,838	4,239
Income (loss) from continuing operations attributable to common stockholders-diluted									30,771	22,058	13,420
Plus: Results from discontinued operations attributable to American Assets Trust, Inc. common stockholders									0	0	25,757
Plus: Results from discontinued operations attributable to unitholders in the Operating Partnership									0	0	11,895
Net income attributable to common stockholders-diluted									$ 30,771	$ 22,058	$ 51,072
DENOMINATOR
Weighted average shares of common stock outstanding-basic (in shares)									42,041,126	39,539,457	38,736,113
Effect of dilutive securities-conversion of Operating Partnership units									17,906,348	17,976,353	18,317,796
Weighted average common shares outstanding - diluted									59,947,474	57,515,810	57,053,909
Earnings (loss) per common share-basic
Continuing operations (in dollars per share)									$ 0.52	$ 0.38	$ 0.24
Discontinued operations (in dollars per share)									$ 0.00	$ 0.00	$ 0.66
Basic net income attributable to common stockholders per share (in dollars per share)									$ 0.52	$ 0.38	$ 0.90
Earnings (loss) per common share-diluted
Continuing operations (in dollars per share)									$ 0.51	$ 0.38	$ 0.24
Discontinued operations (in dollars per share)									$ 0.00	$ 0.00	$ 0.66
Diluted net income attributable to common stockholders per share (in dollars per share)									$ 0.51	$ 0.38	$ 0.90