Equity of American Assets Trust, Inc. Dividends Declared and Paid on Shares of Common Stock and Noncontrolling Common Units (Details) - $ / shares	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, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Equity [Abstract]
Dividends period	Fourth Quarter 2015	Third Quarter 2015	Second Quarter 2015	First Quarter 2015	Fourth Quarter 2014	Third Quarter 2014	Second Quarter 2014	First Quarter 2014	Fourth Quarter 2013	Third Quarter 2013	Second Quarter 2013	First Quarter 2013
Amount per Share/Unit (in USD per unit)	$ 0.25	$ 0.2325	$ 0.2325	$ 0.2325	$ 0.2325	$ 0.22	$ 0.22	$ 0.22	$ 0.22	$ 0.21	$ 0.21	$ 0.2100	$ 0.95	$ 0.89	$ 0.85
Date dividend to be paid	Dec. 23, 2015	Sep. 25, 2015	Jun. 26, 2015	Mar. 27, 2015	Dec. 26, 2014	Sep. 26, 2014	Jun. 27, 2014	Mar. 28, 2014	Dec. 27, 2013	Sep. 27, 2013	Jun. 28, 2013	Mar. 29, 2013