Document And Entity Information (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Mar. 07, 2012	Jun. 30, 2011
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2011
Document Fiscal Period Focus	FY
Document Fiscal Year Focus	2011
Entity Registrant Name	American Assets Trust, Inc.
Entity Central Index Key	0001500217
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		39,284,593
Entity Well-known Seasoned Issuer	No
Entity Public Float			$ 526.1
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes