DEBT - Summary of Total Unsecured Notes Payable Outstanding (Details) - USD ($) $ in Thousands								6 Months Ended
		Jul. 17, 2019	Jun. 23, 2017	May 11, 2017	Jan. 18, 2017	Sep. 19, 2014	Aug. 19, 2014	Jun. 30, 2020	Dec. 31, 2019	Dec. 31, 2017
Debt Instrument [Line Items]
Debt issuance costs, net								$ 0	$ (1,256)
Debt issuance costs, accumulated amortization								0	814
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								1,200,000	1,200,000
Debt issuance costs, net								(3,709)	(4,220)
Total Debt Outstanding								1,196,291	1,195,780
Debt issuance costs, accumulated amortization								$ 8,346	7,835
American Assets Trust, L.P. | Term Loan A | Interest Rate Swap
Debt Instrument [Line Items]
Derivative fixed interest rate (in percent)								4.08%
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, 2021
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								$ 150,000	150,000
Stated Interest Rate	[1]							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)								2.65%		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
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%		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	[2]							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	[3]							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]							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	[5]							3.91%
Stated Maturity Date								Jul. 30, 2030

[1] The Operating Partnership entered into a one-month forward-starting seven years swap contract on August 19, 2014, which was settled on September 19, 2014 at a gain of approximately $1.6 million. The forward-starting seven-year swap contract was deemed to be a highly effective cash flow hedge, accordingly, the effective interest rate is approximately 3.88% per annum.

[2] The Operating Partnership entered into a treasury lock contract on May 31, 2017, which was settled on June 23, 2017 at a loss of approximately $0.5 million. The treasury lock contract was deemed to be a highly effective cash flow hedge, accordingly, the effective interest rate is approximately 3.85% per annum.

[3] The Operating Partnership entered into forward-starting interest rate swap contracts on March 29, 2016 and April 7, 2016, which were settled on January 18, 2017 at a gain of approximately $10.4 million. The forward-starting interest swap rate contracts were deemed to be a highly effective cash flow hedge, accordingly, the effective interest rate is approximately 3.87% per annum.

[4] 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.

[5] The Operating Partnership entered into a treasury lock contract on June 20, 2019, which was settled on July 17, 2019 at a gain of approximately $0.5 million. The treasury lock contract was deemed to be a highly effective cash flow hedge, accordingly, the effective interest rate is approximately 3.88% per annum.