EQUITY OF AMERICAN ASSETS TRUST, INC. - ATM Equity Program (Details)			3 Months Ended	9 Months Ended
	May. 27, 2015 USD ($) Agent	May. 06, 2013 USD ($) Agent	Sep. 30, 2015 USD ($) $ / shares shares	Sep. 30, 2015 USD ($) $ / shares shares	Sep. 30, 2014 USD ($)
Equity [Line Items]
Proceeds, net				$ 72,836,000	$ 104,148,000
At The Market Equity Program
Equity [Line Items]
Number of shares of common stock issued through ATM programs | shares			466,525	1,612,451
Weighted average price per share | $ / shares			$ 40.85	$ 40.77
Proceeds, gross			$ 19,059,000	$ 65,740,000
Proceeds, net			18,828,000	64,728,000
Aggregate offering price of common share	$ 250,000,000.0	$ 150,000,000.0
Commissions | At The Market Equity Program
Equity [Line Items]
Payments of stock issuance costs			(191,000)	(657,000)
Other Offering Costs | At The Market Equity Program
Equity [Line Items]
Payments of stock issuance costs			$ (40,000)	$ (355,000)
$250.0 Million ATM | At The Market Equity Program
Equity [Line Items]
Number of sales agents | Agent	5
$150.0 Million ATM | At The Market Equity Program
Equity [Line Items]
Number of sales agents | Agent		4