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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Fixed interest rate related to the interest rate derivative.

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DEBT - Summary of Total Unsecured Notes Payable Outstanding (Details) - USD ($) $ in Thousands								3 Months Ended		6 Months Ended
	Jan. 26, 2021	Jul. 17, 2019	Jun. 23, 2017	May 11, 2017	Jan. 18, 2017	Sep. 19, 2014	Aug. 19, 2014	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2018
Debt Instrument [Line Items]
Debt issuance costs, net								$ (645)		$ (645)		$ 0
Debt issuance costs, accumulated amortization								1,425		1,425		0
Early extinguishment of debt								0	$ 0	(4,271)	$ 0
American Assets Trust, L.P.
Debt Instrument [Line Items]
Early extinguishment of debt								0	$ 0	(4,271)	$ 0
American Assets Trust, L.P. \| Forward Contracts
Debt Instrument [Line Items]
Derivative contract term							7 years
Gain on derivative settlement		$ 500		$ 700	$ 10,400	$ 1,600
Loss on derivative settlement			$ 500
American Assets Trust, L.P. \| Unsecured term loans, net
Debt Instrument [Line Items]
Long-term Debt, Principal Balance								1,550,000		1,550,000		1,200,000
Debt issuance costs, net								(12,693)		(12,693)		(3,323)
Total Debt Outstanding								1,537,307		1,537,307		1,196,677
Debt issuance costs, accumulated amortization								$ 9,059		$ 9,059		8,856
American Assets Trust, L.P. \| Term Loan A \| Interest Rate Swap
Debt Instrument [Line Items]
Derivative fixed interest rate (in percent)								4.13%		4.13%
American Assets Trust, L.P. \| Term Loan A \| Unsecured term loans, net
Debt Instrument [Line Items]
Long-term Debt, Principal Balance								$ 100,000		$ 100,000		100,000
Stated Maturity Date										Jan. 09, 2022
American Assets Trust, L.P. \| Senior Guaranteed Notes, Series A \| Forward Contracts
Debt Instrument [Line Items]
Effective rate of debt instrument (in percent)								3.88%		3.88%
American Assets Trust, L.P. \| Senior Guaranteed Notes, Series A \| Unsecured term loans, net
Debt Instrument [Line Items]
Long-term Debt, Principal Balance								$ 0		$ 0		150,000
Stated Interest Rate								4.04%		4.04%
Stated Maturity Date										Oct. 31, 2021
Early extinguishment of debt	$ 3,900
American Assets Trust, L.P. \| Term Loan B \| Interest Rate Swap
Debt Instrument [Line Items]
Derivative fixed interest rate (in percent)								2.65%		2.65%			3.15%
American Assets Trust, L.P. \| Term Loan B \| Unsecured term loans, net
Debt Instrument [Line Items]
Long-term Debt, Principal Balance								$ 100,000		$ 100,000		100,000
Stated Maturity Date										Mar. 01, 2023
American Assets Trust, L.P. \| Term Loan C \| Interest Rate Swap
Debt Instrument [Line Items]
Derivative fixed interest rate (in percent)								2.64%		2.64%			3.14%
American Assets Trust, L.P. \| Term Loan C \| Unsecured term loans, net
Debt Instrument [Line Items]
Long-term Debt, Principal Balance								$ 50,000		$ 50,000		50,000
Stated Maturity Date										Mar. 01, 2023
American Assets Trust, L.P. \| Senior Guaranteed Notes, Series F \| Forward Contracts
Debt Instrument [Line Items]
Effective rate of debt instrument (in percent)								3.85%		3.85%
American Assets Trust, L.P. \| Senior Guaranteed Notes, Series F \| Unsecured term loans, net
Debt Instrument [Line Items]
Long-term Debt, Principal Balance								$ 100,000		$ 100,000		100,000
Stated Interest Rate								3.78%		3.78%
Stated Maturity Date										Jul. 19, 2024
American Assets Trust, L.P. \| Senior Guaranteed Notes, Series B \| Unsecured term loans, net
Debt Instrument [Line Items]
Long-term Debt, Principal Balance								$ 100,000		$ 100,000		100,000
Stated Interest Rate								4.45%		4.45%
Stated Maturity Date										Feb. 02, 2025
American Assets Trust, L.P. \| Senior Guaranteed Notes, Series C \| Unsecured term loans, net
Debt Instrument [Line Items]
Long-term Debt, Principal Balance								$ 100,000		$ 100,000		100,000
Stated Interest Rate								4.50%		4.50%
Stated Maturity Date										Apr. 01, 2025
American Assets Trust, L.P. \| Senior Guaranteed Notes, Series D \| Forward Contracts
Debt Instrument [Line Items]
Effective rate of debt instrument (in percent)								3.87%		3.87%
American Assets Trust, L.P. \| Senior Guaranteed Notes, Series D \| Unsecured term loans, net
Debt Instrument [Line Items]
Long-term Debt, Principal Balance								$ 250,000		$ 250,000		250,000
Stated Interest Rate								4.29%		4.29%
Stated Maturity Date										Mar. 01, 2027
American Assets Trust, L.P. \| Senior Guaranteed Notes, Series E \| Forward Contracts
Debt Instrument [Line Items]
Effective rate of debt instrument (in percent)								4.18%		4.18%
American Assets Trust, L.P. \| Senior Guaranteed Notes, Series E \| Unsecured term loans, net
Debt Instrument [Line Items]
Long-term Debt, Principal Balance								$ 100,000		$ 100,000		100,000
Stated Interest Rate								4.24%		4.24%
Stated Maturity Date										May 23, 2029
American Assets Trust, L.P. \| Senior Guaranteed Notes, Series G \| Forward Contracts
Debt Instrument [Line Items]
Effective rate of debt instrument (in percent)								3.88%		3.88%
American Assets Trust, L.P. \| Senior Guaranteed Notes, Series G \| Unsecured term loans, net
Debt Instrument [Line Items]
Long-term Debt, Principal Balance								$ 150,000		$ 150,000		150,000
Stated Interest Rate								3.91%		3.91%
Stated Maturity Date										Jul. 30, 2030
American Assets Trust, L.P. \| 3.375% Senior Unsecured Notes
Debt Instrument [Line Items]
Stated Interest Rate	3.375%
American Assets Trust, L.P. \| 3.375% Senior Unsecured Notes \| Unsecured term loans, net
Debt Instrument [Line Items]
Long-term Debt, Principal Balance								$ 500,000		$ 500,000		$ 0
Stated Interest Rate								3.38%		3.38%
Stated Maturity Date										Feb. 01, 2031