Equity of American Assets Trust, Inc. Computation of Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
NUMERATOR
Income from continuing operations									$ 53,915	$ 31,145	$ 22,594
Less: Net income attributable to restricted shares	$ (53)	$ (32)	$ (40)	$ (43)	$ (115)	$ (95)	$ (94)	$ (70)	(168)	(374)	(536)
Less: Income from operations attributable to unitholders in the Operating Partnership									(15,238)	(9,015)	(6,838)
NET INCOME ATTRIBUTABLE TO AMERICAN ASSETS TRUST, INC. STOCKHOLDERS	$ 8,212	$ 13,562	$ 8,708	$ 8,027	$ 7,024	$ 6,417	$ 3,713	$ 4,602	38,509	21,756	15,220
Income from operations attributable to American Assets Trust, Inc. common stockholders—basic									38,509	21,756	15,220
Plus: Income from operations attributable to unitholders in the Operating Partnership									15,238	9,015	6,838
Net income attributable to common stockholders-diluted									$ 53,747	$ 30,771	$ 22,058
DENOMINATOR
Weighted average shares of common stock outstanding-basic (in shares)									44,439,112	42,041,126	39,539,457
Effect of dilutive securities-conversion of Operating Partnership units (in shares)									17,900,051	17,906,348	17,976,353
Weighted average common shares outstanding - diluted (in shares)									62,339,163	59,947,474	57,515,810
Earnings (loss) per common share-basic
Basic net income attributable to common stockholders per share (in dollars per share)									$ 0.87	$ 0.52	$ 0.38
Earnings (loss) per common share-diluted
Diluted net income attributable to common stockholders per share (in dollars per share)									$ 0.86	$ 0.51	$ 0.38