Equity of American Assets Trust, Inc. (Details)					1 Months Ended	12 Months Ended
	May 27, 2015 USD ($) Agent	Mar. 09, 2015 USD ($) $ / shares shares	Sep. 12, 2014 USD ($) $ / shares shares	May 06, 2013 USD ($) Agent	Jan. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) shares	Dec. 31, 2014 USD ($) shares
Equity [Line Items]
Preferred stock, shares authorized (in shares) | shares						10,000,000
Preferred stock, par-value (in dollars per share) | $ / shares						$ 0.01
Preferred stock, shares issued (in shares) | shares						0
Preferred stock, shares outstanding (in shares) | shares						0
Equity incentive award plan, common stock authorized for issuance (in shares) | shares						4,054,411
Equity incentive award plan, common stock available for future issuance (in shares) | shares						2,945,517
Noncash compensation expense | $						$ 2,400,000	$ 2,900,000	$ 3,700,000
Unrecognized compensation expense | $						$ 3,700,000
Weighted average unvested shares outstanding (in shares) | shares						176,408	184,545	430,584
American Assets Trust, L.P.
Equity [Line Items]
Antidilutive securities excluded from computation of EPS (in shares) | shares						176,408	184,545	430,584
Restricted Stock
Equity [Line Items]
Unrecognized compensation expense, weighted-average recognition period (in years)						1 year 8 months
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						219,480
Weighted average price per share (in dollars per share) | $ / shares						$ 45.50
Gross proceeds from issuance of common stock | $						$ 10,000,000
Remaining capacity available for issuance | $						206,600,000
At The Market Equity Program | Commissions
Equity [Line Items]
Payments of stock issuance costs | $						(100,000)
At The Market Equity Program | Other Offering Costs
Equity [Line Items]
Payments of stock issuance costs | $						$ (200,000)
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 | Insurance Company of the West, Inc. | 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
Subsequent Event | At The Market Equity Program
Equity [Line Items]
Common shares issued (in shares) | shares					700,000
Weighted average price per share (in dollars per share) | $ / shares					$ 43.46
Gross proceeds from issuance of common stock | $					$ 30,400,000
Subsequent Event | At The Market Equity Program | Commissions
Equity [Line Items]
Payments of stock issuance costs | $					$ (300,000)