Cover Page - USD ($)	12 Months Ended
	Dec. 31, 2021	Feb. 11, 2022	Jun. 30, 2021
Document Information [Line Items]
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
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, 2021
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	3420 Carmel Mountain Road
Entity Address, Address Line Two	Suite 100
Entity Address, City or Town	San Diego
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	92121
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
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 1,971,000,000
Entity Common Stock, Shares Outstanding		60,523,831
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