Equity of American Assets Trust, Inc. Summary of Income Tax Status of Dividends Per Share Paid (Details) - $ / shares	3 Months Ended												12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity [Abstract]
Ordinary income (in USD per share)													$ 1.05	$ 1.05	$ 1.01
Capital gain (in USD per share)													0.00	0.00	0.00
Return of capital (in USD per share)													0.04	0.00	0.00
Total (in USD per share)	$ 0.28	$ 0.27	$ 0.27	$ 0.27	$ 0.27	$ 0.26	$ 0.26	$ 0.26	$ 0.26	$ 0.25	$ 0.25	$ 0.25	$ 1.09	$ 1.05	$ 1.01
Ordinary income													96.30%	100.00%	100.00%
Capital gain													0.00%	0.00%	0.00%
Return of capital													3.70%	0.00%	0.00%
Total													100.00%	100.00%	100.00%