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Partners Capital of American Assets Trust, L.P. (Details)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Capital Unit [Line Items]      
Noncontrolling common units 17,905,257aat_SharesHeldByMinorityInterestInOperatingPartnerships    
Noncontrolling Interest, Ownership Percentage by Parent 70.70%us-gaap_MinorityInterestOwnershipPercentageByParent    
Percentage of ownership interests classified as noncontrolling 29.30%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners    
Common Stock      
Capital Unit [Line Items]      
Conversion of operating partnership units (in shares) 11,852us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_CommonStockMember		 106,326us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_CommonStockMember		 372,654us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_CommonStockMember