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, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
NUMERATOR
Net income from operations									$ 36,593	$ 35,588	$ 60,188
Less: Net income attributable to restricted shares	$ (147)	$ (145)	$ (135)	$ (137)	$ (123)	$ (87)	$ (69)	$ (104)	(564)	(383)	(381)
Less: Income attributable to unitholders in the Operating Partnership									7,653	7,545	14,089
NET INCOME ATTRIBUTABLE TO AMERICAN ASSETS TRUST, INC. STOCKHOLDERS									28,376	27,660	45,718
Income attributable to American Assets Trust, Inc. common stockholders—basic									28,376	27,660	45,718
Plus: Income attributable to unitholders in the Operating Partnership									(7,653)	(7,545)	(14,089)
Net income attributable to common stockholders-diluted									$ 36,029	$ 35,205	$ 59,807
DENOMINATOR
Weighted average shares of common stock outstanding-basic (in shares)									59,990,740	59,806,309	54,110,949
Effect of dilutive securities-conversion of Operating Partnership units (in shares)									16,181,537	16,313,454	16,675,183
Weighted average common shares outstanding - diluted (in shares)									76,172,277	76,119,763	70,786,132
Earnings (loss) per common share-basic
Basic net income attributable to common stockholders per share (in dollars per share)									$ 0.47	$ 0.46	$ 0.84
Earnings (loss) per common share-diluted
Diluted net income attributable to common stockholders per share (in dollars per share)									$ 0.47	$ 0.46	$ 0.84