EQUITY OF AMERICAN ASSETS TRUST, INC. - Narrative (Details)			3 Months Ended		9 Months Ended
	Mar. 02, 2018 Agent	May 27, 2015 USD ($) Agent	Sep. 30, 2020 USD ($) shares	Sep. 30, 2019 USD ($) shares	Sep. 30, 2020 USD ($) shares	Sep. 30, 2019 USD ($) shares
Equity [Line Items]
Noncash compensation expense			$ 1,300,000	$ 1,100,000	$ 3,800,000	$ 3,400,000
Unrecognized compensation expense			3,600,000		3,600,000
At The Market Equity Program
Equity [Line Items]
Number of sales agents | Agent	1	5
Aggregate offering price of common share		$ 250,000,000.0
Remaining capacity to issue			$ 132,600,000		$ 132,600,000
Operating Partnership Units
Equity [Line Items]
Antidilutive securities excluded from computation of EPS (in shares) | shares			346,434	329,652	345,613	331,245
American Assets Trust, L.P. | Operating Partnership Units
Equity [Line Items]
Weighted average unvested shares outstanding (in shares) | shares			346,434	329,652	345,613	331,245
Antidilutive securities excluded from computation of EPS (in shares) | shares			346,434	329,652	345,613	331,245