Debt (Details)										12 Months Ended
		Jan. 09, 2018 USD ($) Extension_Option	Apr. 25, 2017	May 02, 2016 USD ($)	Mar. 23, 2016	Mar. 01, 2016 USD ($)	Jan. 29, 2016	Oct. 31, 2014 USD ($)	Jan. 09, 2014 USD ($) Extension_Option	Dec. 31, 2017 USD ($) Extension_Option		Jul. 19, 2017 USD ($)	May 23, 2017 USD ($)	Mar. 01, 2017 USD ($)	Dec. 31, 2016 USD ($)
Debt Instrument [Line Items]
Unsecured line of credit										$ 0					$ 20,000,000
Unsecured notes payable										1,045,470,000					596,350,000
Unsecured line of credit
Debt Instrument [Line Items]
Minimum fixed charge coverage ratio covenant threshold									1.5
Minimum interest coverage ratio covenant threshold									175.00%
Minimum tangible net worth									$ 721,160,000.00
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%
Unsecured line of credit | Federal Funds Rate
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)									0.50%
Unsecured line of credit | Eurodollar
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)									1.00%
Term Loan B | Unsecured debt | Federal Funds Rate
Debt Instrument [Line Items]
Basis spread on federal funds rate						0.50%
Term Loan B | Unsecured debt | Eurodollar
Debt Instrument [Line Items]
Basis spread on Eurodollar rate						1.00%
American Assets Trust, L.P.
Debt Instrument [Line Items]
Unsecured line of credit										0					20,000,000
Unsecured notes payable										1,045,470,000					596,350,000
American Assets Trust, L.P. | Unsecured line of credit | Base Rate
Debt Instrument [Line Items]
Variable rate basis									base rate
American Assets Trust, L.P. | Unsecured line of credit | Revolving Credit Facility
Debt Instrument [Line Items]
Number of extensions available | Extension_Option									2
Extension term (in months)									6 months
American Assets Trust, L.P. | Unsecured debt
Debt Instrument [Line Items]
Unsecured notes payable										$ 1,045,470,000					$ 596,350,000
American Assets Trust, L.P. | Term Loan A
Debt Instrument [Line Items]
Number of extensions available | Extension_Option										3
Extension term (in months)										12 months
Unsecured notes payable									$ 100,000,000
American Assets Trust, L.P. | Term Loan A | Unsecured debt
Debt Instrument [Line Items]
Stated Maturity Date	[1]									Jan. 09, 2019
American Assets Trust, L.P. | Term Loan B
Debt Instrument [Line Items]
Number of year amortization schedule						7 years
Face amount of debt						$ 100,000,000
Stated Maturity Date						Mar. 01, 2023	Mar. 01, 2023
American Assets Trust, L.P. | Term Loan B | Minimum | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)						0.70%
American Assets Trust, L.P. | Term Loan B | Maximum | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)						1.35%
American Assets Trust, L.P. | Term Loan B | Unsecured debt
Debt Instrument [Line Items]
Face amount of debt						$ 100,000,000
Stated Maturity Date										Mar. 01, 2023
American Assets Trust, L.P. | Term Loan B | Unsecured debt | LIBOR
Debt Instrument [Line Items]
Variable rate basis						LIBOR
American Assets Trust, L.P. | Term Loan B | Unsecured debt | Base Rate
Debt Instrument [Line Items]
Minimum base rate						0.00%
Prime rate						prime rate
Federal funds rate						federal funds rate
Eurodollar						Eurodollar
American Assets Trust, L.P. | Term Loan B | Unsecured debt | Minimum | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)						1.70%
American Assets Trust, L.P. | Term Loan B | Unsecured debt | Maximum | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)						2.35%
American Assets Trust, L.P. | Term Loan C
Debt Instrument [Line Items]
Number of year amortization schedule				7 years
Face amount of debt				$ 50,000,000
Stated Maturity Date				Mar. 01, 2023	Mar. 01, 2023
American Assets Trust, L.P. | Term Loan C | Minimum | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)				0.70%
American Assets Trust, L.P. | Term Loan C | Maximum | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)				1.35%
American Assets Trust, L.P. | Term Loan C | Unsecured debt
Debt Instrument [Line Items]
Face amount of debt				$ 50,000,000
Stated Maturity Date										Mar. 01, 2023
American Assets Trust, L.P. | Term Loan C | Unsecured debt | LIBOR
Debt Instrument [Line Items]
Variable rate basis				LIBOR
American Assets Trust, L.P. | Term Loan C | Unsecured debt | Base Rate
Debt Instrument [Line Items]
Minimum base rate				0.00%
Prime rate				prime rate
Federal funds rate				federal funds rate
Eurodollar				Eurodollar
American Assets Trust, L.P. | Term Loan C | Unsecured debt | Minimum | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)				1.70%
American Assets Trust, L.P. | Term Loan C | Unsecured debt | Maximum | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)				2.35%
American Assets Trust, L.P. | Note Purchase Agreement | Senior Guaranteed Notes
Debt Instrument [Line Items]
Face amount of debt								$ 350,000,000
Partial debt repayment, minimum percentage of principal (in percent)								5.00%
Full debt repayment percentage of principal plus a Make-Whole Amount (in percent)								100.00%
American Assets Trust, L.P. | Note Purchase Agreement | Senior Guaranteed Notes, Series A
Debt Instrument [Line Items]
Face amount of debt								$ 150,000,000
Stated Interest Rate								4.04%
American Assets Trust, L.P. | Note Purchase Agreement | Senior Guaranteed Notes, Series B
Debt Instrument [Line Items]
Face amount of debt								$ 100,000,000
Stated Interest Rate								4.45%
American Assets Trust, L.P. | Note Purchase Agreement | Senior Guaranteed Notes, Series C
Debt Instrument [Line Items]
Face amount of debt								$ 100,000,000
Stated Interest Rate								4.50%
American Assets Trust, L.P. | Amended and Restated Credit Facility
Debt Instrument [Line Items]
Revolving credit facility borrowing limit, maximum borrowing capacity									350,000,000
Allowable additional borrowing capacity									$ 250,000,000
American Assets Trust, L.P. | Amended and Restated Credit Facility | Minimum | Revolving Credit Facility | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)									0.35%
American Assets Trust, L.P. | Amended and Restated Credit Facility | Maximum | Revolving Credit Facility | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)									0.95%
American Assets Trust, L.P. | Amended and Restated Credit Facility | Unsecured line of credit
Debt Instrument [Line Items]
Unsecured line of credit										$ 0
Weighted average interest rate (in percent)										2.36%
American Assets Trust, L.P. | Amended and Restated Credit Facility | Unsecured line of credit | Base Rate
Debt Instrument [Line Items]
Prime rate									prime rate
Federal funds rate									federal funds rate
Eurodollar									Eurodollar
American Assets Trust, L.P. | Amended and Restated Credit Facility | Unsecured line of credit | Revolving Credit Facility
Debt Instrument [Line Items]
Revolving credit facility borrowing limit, maximum borrowing capacity									$ 250,000,000
American Assets Trust, L.P. | Amended and Restated Credit Facility | Unsecured line of credit | Revolving Credit Facility | LIBOR
Debt Instrument [Line Items]
Variable rate basis									LIBOR
American Assets Trust, L.P. | Amended and Restated Credit Facility | Unsecured line of credit | Minimum | Revolving Credit Facility | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)									1.35%
American Assets Trust, L.P. | Amended and Restated Credit Facility | Unsecured line of credit | Maximum | Revolving Credit Facility | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)									1.95%
American Assets Trust, L.P. | Amended and Restated Credit Facility | Unsecured debt
Debt Instrument [Line Items]
Revolving credit facility borrowing limit, maximum borrowing capacity									$ 100,000,000
Number of extensions available | Extension_Option									3
Extension term (in months)									12 months
American Assets Trust, L.P. | Amended and Restated Credit Facility | Unsecured debt | Minimum | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)									1.30%
American Assets Trust, L.P. | Amended and Restated Credit Facility | Unsecured debt | Minimum | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)									0.30%
American Assets Trust, L.P. | Amended and Restated Credit Facility | Unsecured debt | Maximum | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)									1.90%
American Assets Trust, L.P. | Amended and Restated Credit Facility | Unsecured debt | Maximum | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)									0.90%
American Assets Trust, L.P. | Senior Guaranteed Notes, Series D | Unsecured debt
Debt Instrument [Line Items]
Face amount of debt														$ 250,000,000
Stated Maturity Date										Mar. 01, 2027
Stated Interest Rate										4.29%				4.29%
American Assets Trust, L.P. | Senior Guaranteed Notes, Series E | Unsecured debt
Debt Instrument [Line Items]
Number of year amortization schedule			12 years
Face amount of debt													$ 100,000,000
Stated Maturity Date										May 23, 2029
Stated Interest Rate										4.24%	[2]		4.24%
American Assets Trust, L.P. | Senior Guaranteed Notes, Series F | Unsecured debt
Debt Instrument [Line Items]
Face amount of debt												$ 100,000,000
Stated Maturity Date										Jul. 19, 2024
Stated Interest Rate										3.78%		3.78%
Interest Rate Swap | American Assets Trust, L.P.
Debt Instrument [Line Items]
Fixed interest rate on derivative										3.08%
Interest Rate Swap | American Assets Trust, L.P. | Term Loan B
Debt Instrument [Line Items]
Fixed interest rate on derivative										3.15%
Interest Rate Swap | American Assets Trust, L.P. | Term Loan C
Debt Instrument [Line Items]
Fixed interest rate on derivative										3.14%
Subsequent Event | Unsecured line of credit
Debt Instrument [Line Items]
Maximum leverage ratio of revolving credit facility		60.00%
Maximum secured leverage ratio on revolving credit facility		40.00%
Minimum fixed charge coverage ratio covenant threshold		1.5
Minimum interest coverage ratio covenant threshold		175.00%
Maximum unsecured leverage ratio (in percents)		60.00%
Maximum recourse indebtedness of total asset value (in percents)		15.00%
Subsequent Event | Unsecured line of credit | Federal Funds Rate
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)		0.50%
Subsequent Event | Unsecured line of credit | Eurodollar
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)		1.00%
Subsequent Event | Term Loan B | Unsecured debt | Federal Funds Rate
Debt Instrument [Line Items]
Basis spread on federal funds rate		0.50%
Subsequent Event | Term Loan B | Unsecured debt | Eurodollar
Debt Instrument [Line Items]
Basis spread on Eurodollar rate		0.10%
Subsequent Event | Term Loan C | Unsecured debt | Federal Funds Rate
Debt Instrument [Line Items]
Basis spread on federal funds rate		0.50%
Subsequent Event | Term Loan C | Unsecured debt | Eurodollar
Debt Instrument [Line Items]
Basis spread on Eurodollar rate		0.10%
Subsequent Event | American Assets Trust, L.P. | Term Loan B
Debt Instrument [Line Items]
Number of year amortization schedule		7 years
Subsequent Event | American Assets Trust, L.P. | Term Loan B | Minimum | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)		0.70%
Subsequent Event | American Assets Trust, L.P. | Term Loan B | Maximum | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)		1.35%
Subsequent Event | American Assets Trust, L.P. | Term Loan B | Unsecured debt | LIBOR
Debt Instrument [Line Items]
Variable rate basis		LIBOR
Subsequent Event | American Assets Trust, L.P. | Term Loan B | Unsecured debt | Base Rate
Debt Instrument [Line Items]
Minimum base rate		0.00%
Prime rate		prime rate
Federal funds rate		federal funds rate
Eurodollar		Eurodollar
Subsequent Event | American Assets Trust, L.P. | Term Loan B | Unsecured debt | Minimum | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)		1.20%
Subsequent Event | American Assets Trust, L.P. | Term Loan B | Unsecured debt | Maximum | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)		1.70%
Subsequent Event | American Assets Trust, L.P. | Term Loan B & Term Loan C | Unsecured debt
Debt Instrument [Line Items]
Face amount of debt		$ 150,000,000
Subsequent Event | American Assets Trust, L.P. | Term Loan C
Debt Instrument [Line Items]
Number of year amortization schedule		7 years
Subsequent Event | American Assets Trust, L.P. | Term Loan C | Minimum | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)		0.70%
Subsequent Event | American Assets Trust, L.P. | Term Loan C | Maximum | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)		1.35%
Subsequent Event | American Assets Trust, L.P. | Term Loan C | Unsecured debt | LIBOR
Debt Instrument [Line Items]
Variable rate basis		LIBOR
Subsequent Event | American Assets Trust, L.P. | Term Loan C | Unsecured debt | Base Rate
Debt Instrument [Line Items]
Minimum base rate		0.00%
Prime rate		prime rate
Federal funds rate		federal funds rate
Eurodollar		Eurodollar
Subsequent Event | American Assets Trust, L.P. | Term Loan C | Unsecured debt | Minimum | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)		1.20%
Subsequent Event | American Assets Trust, L.P. | Term Loan C | Unsecured debt | Maximum | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)		1.70%
Subsequent Event | American Assets Trust, L.P. | Second Amended and Restated Credit Facility
Debt Instrument [Line Items]
Revolving credit facility borrowing limit, maximum borrowing capacity		$ 450,000,000
Allowable additional borrowing capacity		$ 350,000,000
Subsequent Event | American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Unsecured line of credit | Base Rate
Debt Instrument [Line Items]
Prime rate		prime rate
Federal funds rate		federal funds rate
Subsequent Event | American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Unsecured line of credit | Revolving Credit Facility
Debt Instrument [Line Items]
Revolving credit facility borrowing limit, maximum borrowing capacity		$ 350,000,000
Number of extensions available | Extension_Option		2
Extension term (in months)		6 months
Subsequent Event | American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Unsecured line of credit | Revolving Credit Facility | LIBOR
Debt Instrument [Line Items]
Variable rate basis		LIBOR
Subsequent Event | American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Unsecured line of credit | Minimum | Revolving Credit Facility | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)		1.05%
Subsequent Event | American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Unsecured line of credit | Minimum | Revolving Credit Facility | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)		0.10%
Subsequent Event | American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Unsecured line of credit | Maximum | Revolving Credit Facility | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)		1.50%
Subsequent Event | American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Unsecured line of credit | Maximum | Revolving Credit Facility | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)		0.50%
Subsequent Event | American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Unsecured debt
Debt Instrument [Line Items]
Revolving credit facility borrowing limit, maximum borrowing capacity		$ 100,000,000
Subsequent Event | American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Unsecured debt | Minimum | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)		1.30%
Subsequent Event | American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Unsecured debt | Minimum | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)		0.30%
Subsequent Event | American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Unsecured debt | Maximum | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)		1.90%
Subsequent Event | American Assets Trust, L.P. | Second Amended and Restated Credit Facility | Unsecured debt | Maximum | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate (in percents)		0.90%

[1] The Operating Partnership's Term Loan had an original maturity date of January 9, 2016 with an option to extend the Term Loan up to three times, with each such extension for a 12-month period, which we plan to exercise. The foregoing extension options are exercisable by the Operating Partnership subject to the satisfaction of certain conditions. On January 8, 2016, the Operating Partnership exercised the first of three options to extend the maturity date of the Term Loan to January 9, 2017. Effective as of January 9, 2017, the Operating Partnership exercised the second of three options to extend the maturity date of the Term Loan to January 9, 2018.

[2] The Operating Partnership entered into a treasury lock contract on April 25, 2017, which was settled on May 11, 2017 at a gain of approximately $0.7 million. The treasury lock contract was deemed to be a highly effective cash flow hedge, accordingly, the effective interest rate is approximately 4.18% per annum.