Equity of American Assets Trust, Inc. (Details)			3 Months Ended			12 Months Ended
	Sep. 12, 2014 USD ($) $ / shares shares	May. 06, 2013 USD ($) Agent	Mar. 31, 2014 shares	Mar. 31, 2013 shares	Mar. 31, 2012 shares	Dec. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2013 USD ($) shares	Dec. 31, 2012 USD ($) shares
Equity [Line Items]
Noncontrolling common units						17,905,257
Noncontrolling Interest, Ownership Percentage by Parent						70.70%
Percentage of ownership interests classified as noncontrolling						29.30%
Preferred stock, shares authorized						10,000,000
Preferred stock, par-value | $ / shares						$ 0.01
Equity incentive award plan, common stock authorized for issuance						4,054,411
Equity incentive award plan, common stock available for future issuance						3,560,872
Noncash compensation expense recognized | $						$ 3,700,000	$ 2,800,000	$ 2,900,000
Unrecognized compensation expense | $						$ 5,100,000
Weighted average unvested shares outstanding						430,584	630,130	629,493
Restricted Stock
Equity [Line Items]
Unrecognized compensation expense, weighted-average recognition period (in years)						11 months 19 days
At The Market Equity Program
Equity [Line Items]
Number of Sales Agents | Agent		4
Aggregate Offering Price Of Common Share | $		$ 150,000,000.0
Common shares issued (in shares)						2,710,067
Weighted average price per share | $ / shares						$ 33.84
Proceeds from Issuance of Common Stock, Gross | $						$ 91,700,000
Remaining capacity available for issuance | $						32,300,000
Commissions | At The Market Equity Program
Equity [Line Items]
Payments of Stock Issuance Costs | $						(900,000)
Other Offering Costs | At The Market Equity Program
Equity [Line Items]
Payments of Stock Issuance Costs | $						$ (100,000)
ICW Plaza | Board of Directors Chairman | Private Placement
Equity [Line Items]
Common shares issued (in shares)	400,000
Share Price | $ / shares	$ 33.76
Proceeds from Issuance of Common Stock, Gross | $	$ 13,500,000
American Assets Trust, L.P.
Equity [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount			430,584	630,130	629,493