Equity of American Assets Trust, Inc. (Details)					12 Months Ended
	May. 27, 2015 USD ($) Agent	Mar. 09, 2015 USD ($) $ / shares shares	Sep. 12, 2014 USD ($) $ / shares shares	May. 06, 2013 USD ($) Agent	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) shares	Dec. 31, 2013 USD ($) shares
Equity [Line Items]
Preferred stock, shares authorized | shares					10,000,000
Preferred stock, par-value (in dollars per share) | $ / shares					$ 0.01
Equity incentive award plan, common stock authorized for issuance | shares					4,054,411
Equity incentive award plan, common stock available for future issuance | shares					3,093,627
Noncash compensation expense					$ 2,900,000	$ 3,700,000	$ 2,800,000
Unrecognized compensation expense					$ 2,800,000
Weighted average unvested shares outstanding | shares					184,545	430,584	630,130
American Assets Trust, L.P.
Equity [Line Items]
Antidilutive securities excluded from computation of EPS (in shares) | shares					184,545	430,584	630,130
Restricted Stock
Equity [Line Items]
Unrecognized compensation expense, weighted-average recognition period (in years)					18 months 25 days
At The Market Equity Program
Equity [Line Items]
Aggregate offering price of common share	$ 250,000,000.0			$ 150,000,000.0
Common shares issued (in shares) | shares					1,612,451
Weighted average price per share (in dollars per share) | $ / shares					$ 40.77
Gross proceeds from issuance of common stock					$ 65,700,000
Remaining capacity available for issuance					216,600,000
At The Market Equity Program | Commissions
Equity [Line Items]
Payments of stock issuance costs					(700,000)
At The Market Equity Program | Other Offering Costs
Equity [Line Items]
Payments of stock issuance costs					$ (400,000)
Private Placement | Explorer Insurance Company | Board of Directors Chairman
Equity [Line Items]
Common shares issued (in shares) | shares		200,000
Gross proceeds from issuance of common stock		$ 8,100,000
Share price (in dollars per share) | $ / shares		$ 40.54
Private Placement | ICW Plaza | Board of Directors Chairman
Equity [Line Items]
Common shares issued (in shares) | shares			400,000
Gross proceeds from issuance of common stock			$ 13,500,000
Share price (in dollars per share) | $ / shares			$ 33.76
$150.0 Million ATM | At The Market Equity Program
Equity [Line Items]
Number of sales agents | Agent				4
$250.0 Million ATM | At The Market Equity Program
Equity [Line Items]
Number of sales agents | Agent	5