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DEBT - Summary of Total Unsecured Notes Payable Outstanding (Details) - American Assets Trust, L.P. $ in Thousands	Jul. 17, 2019 USD ($)	Jun. 23, 2017 USD ($)	May 11, 2017 USD ($)	Jan. 18, 2017 USD ($)	Sep. 30, 2022 USD ($) interest_rate_swap_agreement	Dec. 31, 2021 USD ($)	Jan. 26, 2021	Mar. 01, 2018
Forward Contracts
Debt Instrument [Line Items]
Loss on derivative settlement		$ 500
Gain on derivative settlement	$ 500		$ 700	$ 10,400
Unsecured term loans, net
Debt Instrument [Line Items]
Long-term debt, principal balance					$ 1,550,000	$ 1,550,000
Debt issuance costs, net					(11,014)	(11,762)
Total Debt Outstanding					1,538,986	1,538,238
Debt issuance costs, accumulated amortization					$ 11,242	9,462
Term Loan A \| Interest Rate Swap
Debt Instrument [Line Items]
Number of interest rate \| interest_rate_swap_agreement					2
Derivative fixed interest rate (in percent)					2.70%
Term Loan A \| Unsecured term loans, net
Debt Instrument [Line Items]
Long-term debt, principal balance					$ 100,000	100,000
Term Loan B \| Interest Rate Swap
Debt Instrument [Line Items]
Derivative fixed interest rate (in percent)					3.15%			2.65%
Term Loan B \| Unsecured term loans, net
Debt Instrument [Line Items]
Long-term debt, principal balance					$ 100,000	100,000
Term Loan C \| Interest Rate Swap
Debt Instrument [Line Items]
Derivative fixed interest rate (in percent)					3.14%			2.64%
Term Loan C \| Unsecured term loans, net
Debt Instrument [Line Items]
Long-term debt, principal balance					$ 50,000	50,000
Senior Guaranteed Notes, Series F \| Forward Contracts
Debt Instrument [Line Items]
Effective rate of debt instrument (in percent)					3.85%
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%
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%
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%
Senior Guaranteed Notes, Series D \| Forward Contracts
Debt Instrument [Line Items]
Effective rate of debt instrument (in percent)					3.87%
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%
Senior Guaranteed Notes, Series E \| Forward Contracts
Debt Instrument [Line Items]
Effective rate of debt instrument (in percent)					4.18%
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%
Senior Guaranteed Notes, Series G \| Forward Contracts
Debt Instrument [Line Items]
Effective rate of debt instrument (in percent)					3.88%
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%
3.375% Senior Unsecured Notes
Debt Instrument [Line Items]
Stated interest rate							3.375%
3.375% Senior Unsecured Notes \| Unsecured term loans, net
Debt Instrument [Line Items]
Long-term debt, principal balance					$ 500,000	$ 500,000
Stated interest rate					3.375%