EQUITY OF AMERICAN ASSETS TRUST, INC. (Details)				3 Months Ended		6 Months Ended
	Jun. 14, 2019 USD ($) shares	Mar. 02, 2018 Agent	May 27, 2015 USD ($) Agent	Jun. 30, 2019 USD ($) $ / shares shares	Jun. 30, 2018 USD ($) shares	Jun. 30, 2019 USD ($) $ / shares shares	Jun. 30, 2018 USD ($) shares
Equity [Line Items]
Proceeds from issuance of common stock | $	$ 472,600,000					$ 503,014,000
Common stock, shares issued (in shares) | shares	10,925,000
Option Indexed to Issuer's Equity, Indexed Shares | shares	1,425,000
Noncash compensation expense | $				$ 1,100,000	$ 700,000	2,200,000	$ 1,500,000
Unrecognized compensation expense | $				$ 4,400,000		$ 4,400,000
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
Common shares issued (shares) | shares				519,382		681,913
Weighted average price per share | $ / shares				$ 45.57		$ 45.56
Proceeds from issuance of common stock | $				$ 23,355,000		$ 30,388,000
Remaining capacity to issue | $				$ 145,100,000		$ 145,100,000
Operating Partnership Units
Equity [Line Items]
Antidilutive securities excluded from computation of EPS (in shares) | shares				330,847	266,260	332,054	267,367
American Assets Trust, L.P. | Operating Partnership Units
Equity [Line Items]
Weighted average unvested shares outstanding (in shares) | shares				330,847	266,260	332,054	267,367
Antidilutive securities excluded from computation of EPS (in shares) | shares				330,847	266,260	332,054	267,367