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, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Equity [Abstract]
Ordinary income (in USD per share)													$ 0.66	$ 1.09	$ 1.05
Capital gain (in USD per share)													0	0	0
Return of capital (in USD per share)													0.34	0.05	0.04
Total (in USD per share)	$ 0.25	$ 0.25	$ 0.20	$ 0.30	$ 0.30	$ 0.28	$ 0.28	$ 0.28	$ 0.28	$ 0.27	$ 0.27	$ 0.27	$ 1.00	$ 1.14	$ 1.09
Ordinary income													66.00%	95.60%	96.30%
Capital gain													0.00%	0.00%	0.00%
Return of capital													34.00%	4.40%	3.70%
Total													100.00%	100.00%	100.00%