Debt Summary of Total Unsecured Notes Payable Outstanding (Details)																	12 Months Ended
	Jan. 26, 2021 USD ($)	Oct. 01, 2020 USD ($)	Jul. 17, 2019 USD ($)	Jan. 09, 2019 Extension_Option	Jun. 23, 2017 USD ($)	May 31, 2017	May 11, 2017 USD ($)	Apr. 25, 2017	Jan. 18, 2017 USD ($)	May 02, 2016	Apr. 07, 2016	Mar. 29, 2016	Mar. 23, 2016	Mar. 01, 2016	Jan. 29, 2016	Sep. 19, 2014 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jul. 30, 2019 USD ($)	Dec. 31, 2018	Jan. 09, 2018	Jul. 19, 2017	May 23, 2017	Mar. 01, 2017	Jan. 09, 2014 USD ($)
Debt Instrument [Line Items]
Unsecured notes payable																	$ 1,538,238,000	$ 1,196,677,000
Repayments of Unsecured Debt																	155,375,000	0	$ 0
Loss on early extinguishment of debt																	(4,271,000)	0	0
Repayment of unsecured line of credit																	100,000,000	0	123,000,000
American Assets Trust, L.P.
Debt Instrument [Line Items]
Unsecured notes payable																	1,538,238,000	1,196,677,000
Repayments of Unsecured Debt																	155,375,000	0	0
Loss on early extinguishment of debt																	(4,271,000)	0	0
Repayment of unsecured line of credit																	$ 100,000,000	0	$ 123,000,000
American Assets Trust, L.P. | Interest Rate Swap
Debt Instrument [Line Items]
Term of derivative contract						7 years		10 years			10 years	10 years					7 years
American Assets Trust, L.P. | Forward Contracts
Debt Instrument [Line Items]
Term of derivative contract																	1 month
Gain on derivatives		$ 0	$ 500,000				$ 700,000		$ 10,400,000							$ 1,600,000
Loss on derivatives					$ 500,000
Term Loan A | American Assets Trust, L.P.
Debt Instrument [Line Items]
Unsecured notes payable																										$ 100,000,000
Term Loan A | American Assets Trust, L.P. | Interest Rate Swap
Debt Instrument [Line Items]
Fixed interest rate on derivative																	4.13%
Senior Guaranteed Notes, Series A | American Assets Trust, L.P. | Forward Contracts
Debt Instrument [Line Items]
Effective interest rate (percent)																	3.88%
Term Loan B | American Assets Trust, L.P.
Debt Instrument [Line Items]
Stated Maturity Date														Mar. 01, 2023	Mar. 01, 2023
Term Loan B | American Assets Trust, L.P. | Interest Rate Swap
Debt Instrument [Line Items]
Fixed interest rate on derivative														3.15%			2.65%				3.15%
Term Loan C | American Assets Trust, L.P.
Debt Instrument [Line Items]
Stated Maturity Date										Mar. 01, 2023			Mar. 01, 2023
Term Loan C | American Assets Trust, L.P. | Interest Rate Swap
Debt Instrument [Line Items]
Fixed interest rate on derivative														3.14%			2.64%				3.14%
Senior Guaranteed Notes, Series F | American Assets Trust, L.P. | Forward Contracts
Debt Instrument [Line Items]
Effective interest rate (percent)																	3.85%
Senior Guaranteed Notes, Series D | American Assets Trust, L.P. | Forward Contracts
Debt Instrument [Line Items]
Effective interest rate (percent)																	3.87%
Senior Guaranteed Notes, Series E | American Assets Trust, L.P. | Forward Contracts
Debt Instrument [Line Items]
Effective interest rate (percent)																	4.18%
Senior Guaranteed Notes, Series G [Member] | American Assets Trust, L.P. | Forward Contracts
Debt Instrument [Line Items]
Effective interest rate (percent)																	3.88%
3.375% Senior Unsecured Notes | American Assets Trust, L.P.
Debt Instrument [Line Items]
Stated Interest Rate	3.375%
Note Offering Percent	0.98935
Debt Securities, Held-to-Maturity, Weighted Average Yield, Maturity, after Year 10	3.502%
Proceeds from Debt, Net of Issuance Costs	$ 489,700,000
Unsecured debt
Debt Instrument [Line Items]
Debt issuance costs, accumulated amortization																	$ 387,000	345,000
Unsecured debt | American Assets Trust, L.P.
Debt Instrument [Line Items]
Long-term Debt, Principal Balance																	1,550,000,000	1,200,000,000
Debt issuance costs, net																	(11,762,000)	(3,323,000)
Unsecured notes payable																	1,538,238,000	1,196,677,000
Debt issuance costs, accumulated amortization																	9,462,000	8,856,000
Unsecured debt | Term Loan A | American Assets Trust, L.P.
Debt Instrument [Line Items]
Long-term Debt, Principal Balance																	$ 100,000,000	100,000,000
Stated Maturity Date																	Jan. 09, 2022
Number of extensions available | Extension_Option				3
Extension term (in months)				1 year
Unsecured debt | Senior Guaranteed Notes, Series A | American Assets Trust, L.P.
Debt Instrument [Line Items]
Long-term Debt, Principal Balance																	$ 0	150,000,000
Stated Interest Rate																	4.04%
Stated Maturity Date																	Oct. 31, 2021
Repayments of Unsecured Debt	150,000,000
Loss on early extinguishment of debt	3,900,000
Unsecured debt | Term Loan B | American Assets Trust, L.P.
Debt Instrument [Line Items]
Long-term Debt, Principal Balance																	$ 100,000,000	100,000,000
Stated Maturity Date																	Mar. 01, 2023
Unsecured debt | Term Loan C | American Assets Trust, L.P.
Debt Instrument [Line Items]
Long-term Debt, Principal Balance																	$ 50,000,000	50,000,000
Stated Maturity Date																	Mar. 01, 2023
Unsecured debt | Senior Guaranteed Notes, Series F | American Assets Trust, L.P.
Debt Instrument [Line Items]
Long-term Debt, Principal Balance																	$ 100,000,000	100,000,000
Stated Interest Rate																	3.78%						3.78%
Stated Maturity Date																	Jul. 19, 2024
Unsecured debt | Senior Guaranteed Notes, Series B | American Assets Trust, L.P.
Debt Instrument [Line Items]
Long-term Debt, Principal Balance																	$ 100,000,000	100,000,000
Stated Interest Rate																	4.45%
Stated Maturity Date																	Feb. 02, 2025
Unsecured debt | Senior Guaranteed Notes, Series C | American Assets Trust, L.P.
Debt Instrument [Line Items]
Long-term Debt, Principal Balance																	$ 100,000,000	100,000,000
Stated Interest Rate																	4.50%
Stated Maturity Date																	Apr. 01, 2025
Unsecured debt | Senior Guaranteed Notes, Series D | American Assets Trust, L.P.
Debt Instrument [Line Items]
Long-term Debt, Principal Balance																	$ 250,000,000	250,000,000
Stated Interest Rate																	4.29%								4.29%
Stated Maturity Date																	Mar. 01, 2027
Unsecured debt | Senior Guaranteed Notes, Series E | American Assets Trust, L.P.
Debt Instrument [Line Items]
Long-term Debt, Principal Balance																	$ 100,000,000	100,000,000
Stated Interest Rate																	4.24%							4.24%
Stated Maturity Date																	May 23, 2029
Unsecured debt | Senior Guaranteed Notes, Series G [Member] | American Assets Trust, L.P.
Debt Instrument [Line Items]
Long-term Debt, Principal Balance																		150,000,000		$ 150,000,000
Stated Interest Rate																	3.91%			3.91%
Unsecured debt | 3.375% Senior Unsecured Notes | American Assets Trust, L.P.
Debt Instrument [Line Items]
Long-term Debt, Principal Balance																	$ 500,000,000	$ 0
Stated Interest Rate																	3.38%
Stated Maturity Date																	Feb. 01, 2031
Unsecured line of credit
Debt Instrument [Line Items]
Minimum fixed charge coverage ratio covenant threshold																						1.5				1.5
Unsecured line of credit | Second Amended and Restated Credit Facility | American Assets Trust, L.P.
Debt Instrument [Line Items]
Repayment of unsecured line of credit	$ 100,000,000