| Cover Page | Feb. 11, 2020 |
| Document Information [Line Items] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Feb. 11, 2020 |
| Entity Registrant Name | American Assets Trust, Inc. |
| Entity Central Index Key | 0001500217 |
| Entity Incorporation, State or Country Code | MD |
| Entity File Number | 001-35030 |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, par value $0.01 per share |
| Trading Symbol | AAT |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
