Debt (Details) (USD $)	0 Months Ended					1 Months Ended	0 Months Ended
	Jan. 09, 2014	Sep. 07, 2012	Mar. 29, 2012	Jan. 10, 2012	Mar. 07, 2011	Oct. 31, 2012	Oct. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Oct. 10, 2012	Jan. 19, 2011
Debt Instrument [Line Items]
Unsecured notes payable								$ 250,000,000	$ 0
Line of Credit
Debt Instrument [Line Items]
Maximum leverage ratio of revolving credit facility	60.00%
Percent of net proceeds of any additional equity issuances in relation to net proceeds as of Offering	75.00%
Percentage annual distributions cannot exceed funds from operations	95.00%
Maximum unsecured leverage ratio (in percents)	60.00%
Minimum tangible net worth	721,160,000.00
Maximum recourse indebtedness of total asset value (in percents)	15.00%
Base Rate | Line of Credit
Debt Instrument [Line Items]
Points added to federal funds rate (in percents)	0.50%
Points added to Eurodollar rate (in percents)	1.00%
Prior to December 31, 2015 | Line of Credit
Debt Instrument [Line Items]
Maximum secured leverage ratio on revolving credit facility	45.00%
After December 31, 2015 | Line of Credit
Debt Instrument [Line Items]
Minimum fixed charge coverage ratio on revolving credit facility	1.5
Maximum secured leverage ratio on revolving credit facility	40.00%
Minimum unsecured interest coverage ratio (in percents)	175.00%
American Assets Trust, L.P.
Debt Instrument [Line Items]
Non-recourse mortgage loan						10 years
Original principal amount of non-recourse mortgage loan										111,000,000.0
Maturity date of loan						Nov. 01, 2022
Interest rate						3.98%
Number of year non-recourse mortgage loan			7 years
Principal of non-recourse mortgage loan			21,900,000.0
Stated Interest Rate			3.94%
Revolving credit facility borrowing limit, maximum borrowing capacity	350,000,000										250,000,000.0
Years, maximum maturities of securities					30 years
Year, extension on term of revolving credit facility				1 year
Percent of secured indebtedness of the company's secured total asset value		55.00%
Line of credit facility material acquisition		greater than $100 million
Allowable additional borrowing capacity	250,000,000
Unsecured notes payable								250,000,000	0
American Assets Trust, L.P. | Subject to meeting specified requirements and obtaining additional commitments
Debt Instrument [Line Items]
Revolving credit facility borrowing limit, maximum borrowing capacity											400,000,000.0
American Assets Trust, L.P. | Revolving Credit Facility
Debt Instrument [Line Items]
Revolving credit facility borrowing limit, maximum borrowing capacity	250,000,000
American Assets Trust, L.P. | Revolving Credit Facility | Line of Credit
Debt Instrument [Line Items]
Extension term (in months)	6 months
Number of extensions available	2
American Assets Trust, L.P. | Term Loan
Debt Instrument [Line Items]
Revolving credit facility borrowing limit, maximum borrowing capacity	100,000,000
Unsecured notes payable	100,000,000
American Assets Trust, L.P. | LIBOR | Line of Credit
Debt Instrument [Line Items]
Variable rate basis	LIBOR
American Assets Trust, L.P. | Base Rate | Line of Credit
Debt Instrument [Line Items]
Variable rate basis	base rate
Prime rate	prime rate
Federal funds rate	federal funds
Eurodollar	Eurodollar
American Assets Trust, L.P. | Minimum | LIBOR | Revolving Credit Facility | Line of Credit
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)	1.35%
American Assets Trust, L.P. | Minimum | LIBOR | Term Loan | Line of Credit
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)	1.30%
American Assets Trust, L.P. | Minimum | Base Rate | Revolving Credit Facility | Line of Credit
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)	0.35%
American Assets Trust, L.P. | Minimum | Base Rate | Term Loan | Line of Credit
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)	0.30%
American Assets Trust, L.P. | Maximum | LIBOR | Revolving Credit Facility | Line of Credit
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)	1.95%
American Assets Trust, L.P. | Maximum | LIBOR | Term Loan | Line of Credit
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)	1.90%
American Assets Trust, L.P. | Maximum | Base Rate | Revolving Credit Facility | Line of Credit
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)	0.95%
American Assets Trust, L.P. | Maximum | Base Rate | Term Loan | Line of Credit
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)	0.90%
American Assets Trust, L.P. | Note Purchase Agreement | Senior Notes
Debt Instrument [Line Items]
Principal of non-recourse mortgage loan							350,000,000
Debt Instrument, Partial Repayment, Minimum Percentage of Principal							5.00%
Debt Instrument, Prepayment, Percentage of Principal Plus a Stated Amount							100.00%
American Assets Trust, L.P. | Note Purchase Agreement | Senior Notes, Series A
Debt Instrument [Line Items]
Principal of non-recourse mortgage loan							150,000,000
Stated Interest Rate							4.04%
Senior Notes								150,000,000
Effective interest rate (percent)							3.88%
American Assets Trust, L.P. | Note Purchase Agreement | Senior Notes, Series B
Debt Instrument [Line Items]
Principal of non-recourse mortgage loan							100,000,000
Stated Interest Rate							4.45%
American Assets Trust, L.P. | Note Purchase Agreement | Senior Notes, Series C
Debt Instrument [Line Items]
Principal of non-recourse mortgage loan							$ 100,000,000
Stated Interest Rate							4.50%