Equity of American Assets Trust, Inc. (Details)			12 Months Ended
	Dec. 03, 2021 USD ($) Agent	Jun. 14, 2019 USD ($) shares	Dec. 31, 2021 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 USD ($) shares
Equity [Line Items]
Preferred stock, shares authorized (in shares)			10,000,000
Preferred stock, par-value (in dollars per share) | $ / shares			$ 0.01
Preferred stock, shares issued (in shares)			0
Equity incentive award plan, common stock authorized for issuance (in shares)			4,054,411
Equity incentive award plan, common stock available for future issuance (in shares)			2,402,848
Noncash compensation expense | $			$ 8,500,000	$ 6,300,000	$ 4,500,000
Unrecognized compensation expense | $			8,200,000
Proceeds from issuance of common stock, net | $		$ 472,600,000	$ 0	$ 0	$ 515,354,000
Common stock, shares issued		10,925,000	60,525,580	60,476,292
Option Indexed to Issuer's Equity, Indexed Shares		1,425,000
American Assets Trust, L.P.
Equity [Line Items]
Antidilutive securities excluded from computation of EPS (in shares)			485,202	357,048	330,197
Restricted Stock
Equity [Line Items]
Unrecognized compensation expense, weighted-average recognition period (in years)			1 year 7 months 6 days
At The Market Equity Program
Equity [Line Items]
Aggregate offering price of common share | $	$ 250,000,000
Common shares issued (in shares)			0
Remaining capacity available for issuance | $			$ 250,000,000
$250.0 Million ATM | At The Market Equity Program
Equity [Line Items]
Number of sales agents | Agent	5
Operating Partnership Units | American Assets Trust, L.P.
Equity [Line Items]
Weighted average unvested shares outstanding (in shares)			485,202	357,048	330,197