v3.19.3.a.u2
Cover Page - USD ($)
12 Months Ended
Dec. 31, 2019
Feb. 14, 2020
Jun. 30, 2019
Document Information [Line Items]      
Amendment Flag false    
Current Fiscal Year End Date --12-31    
Document Fiscal Year Focus 2019    
Document Fiscal Period Focus FY    
Trading Symbol AAT    
Entity Central Index Key 0001500217    
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2019    
Document Transition Report false    
Entity Registrant Name AMERICAN ASSETS TRUST, INC.    
Entity File Number 001-35030    
Entity Incorporation, State or Country Code MD    
Entity Tax Identification Number 27-3338708    
Entity Address, Address Line One 11455 El Camino Real    
Entity Address, Address Line Two Suite 200    
Entity Address, City or Town San Diego    
Entity Address, State or Province CA    
Entity Address, Postal Zip Code 92130    
City Area Code 858    
Local Phone Number 350-2600    
Title of 12(b) Security Common Stock, $.01 par value per share    
Security Exchange Name NYSE    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Large Accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Shell Company false    
Entity Public Float     $ 2,491,000,000
Entity Common Stock, Shares Outstanding   60,068,228  
American Assets Trust, L.P.      
Document Information [Line Items]      
Amendment Flag false    
Entity Central Index Key 0001509570    
Document Type 10-K    
Entity Registrant Name AMERICAN ASSETS TRUST, L.P.    
Entity File Number 33-202342-01    
Entity Incorporation, State or Country Code MD    
Entity Tax Identification Number 27-3338894    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Non-accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Shell Company false    
Entity Public Float     $ 0
Entity Common Stock, Shares Outstanding   0