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, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Equity [Abstract]
Dividend Period	Fourth Quarter 2014	Third Quarter 2014	Second Quarter 2014	First Quarter 2014	Fourth Quarter 2013	Third Quarter 2013	Second Quarter 2013	First Quarter 2013	Fourth Quarter 2012	Third Quarter 2012	Second Quarter 2012	First Quarter 2012
Amount per Share/Unit	$ 0.2325	$ 0.22	$ 0.22	$ 0.22	$ 0.22	$ 0.21	$ 0.21	$ 0.2100	$ 0.21	$ 0.21	$ 0.21	$ 0.21	$ 0.89	$ 0.85	$ 0.84
Dividends Period Covered	October 1, 2014 to December 31, 2014	July 1, 2014 to September 30, 2014	April 1, 2014 to June 30, 2014	January 1, 2014 to March 31, 2014	October 1, 2013 to December 31, 2013	July 1, 2013 to September 30, 2013	April 1, 2013 to June 30, 2013	January 1, 2013 to March 31, 2013	October 1, 2012 to December 31, 2012	July 1, 2012 to September 30, 2012	April 1, 2012 to June 30, 2012	January 1, 2012 to March 31, 2012
Dividend Paid Date	Dec. 26, 2014	Sep. 26, 2014	Jun. 27, 2014	Mar. 28, 2014	Dec. 27, 2013	Sep. 27, 2013	Jun. 28, 2013	Mar. 29, 2013	Dec. 28, 2012	Sep. 28, 2012	Jun. 29, 2012	Mar. 30, 2012