Amount of accumulated amortization of debt issuance costs.

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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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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Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Fixed interest rate related to the interest rate derivative.

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Amount of increase in the fair value of derivatives recognized in the income statement.

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Period the derivative contract is outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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DEBT - Summary of Total Unsecured Notes Payable Outstanding (Details) - USD ($) $ in Thousands							3 Months Ended
	Jul. 17, 2019	Jun. 23, 2017	May 11, 2017	Jan. 18, 2017	Sep. 19, 2014	Aug. 19, 2014	Mar. 31, 2021	Jan. 26, 2021	Dec. 31, 2020	Dec. 31, 2018
Debt Instrument [Line Items]
Debt issuance costs, net							$ (746)		$ 0
Debt issuance costs, accumulated amortization							1,324		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		1,200,000
Debt issuance costs, net							(13,110)		(3,323)
Total Debt Outstanding							1,536,890		1,196,677
Debt issuance costs, accumulated amortization							$ 9,463		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%
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
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%
American Assets Trust, L.P. \| Senior Guaranteed Notes, Series A \| Unsecured term loans, net
Debt Instrument [Line Items]
Long-term Debt, Principal Balance							$ 0		150,000
Stated Interest Rate							4.04%
Stated Maturity Date							Oct. 31, 2021
American Assets Trust, L.P. \| Term Loan B \| Interest Rate Swap
Debt Instrument [Line Items]
Derivative fixed interest rate (in percent)							2.75%			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
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)							2.74%			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
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%
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
Stated Interest Rate							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
Stated Interest Rate							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
Stated Interest Rate							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%
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
Stated Interest Rate							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%
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
Stated Interest Rate							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%
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
Stated Interest Rate							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		$ 0
Stated Interest Rate							3.38%
Stated Maturity Date							Feb. 01, 2031