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, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
NUMERATOR
Income from continuing operations									$ 45,637	$ 53,915	$ 31,145
Less: Net income attributable to restricted shares	$ (61)	$ (42)	$ (43)	$ (43)	$ (53)	$ (32)	$ (40)	$ (43)	(189)	(168)	(374)
Less: Income from operations attributable to unitholders in the Operating Partnership									12,863	15,238	9,015
NET INCOME ATTRIBUTABLE TO AMERICAN ASSETS TRUST, INC. STOCKHOLDERS	$ 8,861	$ 8,474	$ 7,599	$ 7,651	$ 8,212	$ 13,562	$ 8,708	$ 8,027	32,585	38,509	21,756
Income from operations attributable to American Assets Trust, Inc. common stockholders—basic									32,585	38,509	21,756
Plus: Income from operations attributable to unitholders in the Operating Partnership									(12,863)	(15,238)	(9,015)
Net income attributable to common stockholders-diluted									$ 45,448	$ 53,747	$ 30,771
DENOMINATOR
Weighted average shares of common stock outstanding-basic (in shares)									45,332,471	44,439,112	42,041,126
Effect of dilutive securities-conversion of Operating Partnership units (in shares)									17,895,688	17,900,051	17,906,348
Weighted average common shares outstanding - diluted (in shares)									63,228,159	62,339,163	59,947,474
Earnings (loss) per common share-basic
Basic net income attributable to common stockholders per share (in dollars per share)									$ 0.72	$ 0.87	$ 0.52
Earnings (loss) per common share-diluted
Diluted net income attributable to common stockholders per share (in dollars per share)									$ 0.72	$ 0.86	$ 0.51