DERIVATIVE AND HEDGING ACTIVITIES (Details) - USD ($)								9 Months Ended
	Aug. 11, 2020	Jul. 17, 2019	Jun. 20, 2019	May 11, 2017	Jan. 18, 2017	Sep. 19, 2014	Aug. 19, 2014	Sep. 30, 2020
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Estimated derivative reclassification from Accumulated OCI to Income								$ 1,300,000
American Assets Trust, L.P. | Forward Contracts
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative contract term							7 years
Gain on derivative settlement		$ 500,000		$ 700,000	$ 10,400,000	$ 1,600,000
Designated as Hedging Instrument | Cash Flow Hedging | American Assets Trust, L.P. | Interest Rate Swap, 1/9/2021 | Bank of America, N.A.
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amount								$ 100,000,000
Effective Date								Jan. 09, 2019
Maturity Date								Jan. 09, 2021
Interest rate swap liability								$ (779,000)
Interest Rate Derivative Liabilities, at Fair Value								779,000
Designated as Hedging Instrument | Cash Flow Hedging | American Assets Trust, L.P. | Interest Rate Swap, 3/1/2023 | Wells Fargo Bank, N.A.
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amount								$ 50,000,000
Effective Date								May 02, 2016
Maturity Date								Mar. 01, 2023
Interest rate swap liability								$ (1,659,000)
Interest Rate Derivative Liabilities, at Fair Value								1,659,000
Designated as Hedging Instrument | Cash Flow Hedging | American Assets Trust, L.P. | Interest Rate Swap, 3/1/2023 | U.S. Bank N.A.
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amount								$ 100,000,000
Effective Date								Mar. 01, 2016
Maturity Date								Mar. 01, 2023
Interest rate swap liability								$ (3,344,000)
Interest Rate Derivative Liabilities, at Fair Value								3,344,000
Designated as Hedging Instrument | Cash Flow Hedging | American Assets Trust, L.P. | Treasury Lock | Wells Fargo Bank, N.A.
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative fixed interest rate (in percent)			1.9925%
Derivative contract term			10 years
Notional Amount			$ 100,000,000
Maturity Date			Jul. 31, 2019
Amortization Period of Deferred Gain (Loss) on Discontinuation of Fair Value Hedge			10 years
Not Designated as Hedging Instrument | American Assets Trust, L.P. | Treasury Lock | Wells Fargo Bank, N.A.
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative fixed interest rate (in percent)	0.7115%
Derivative contract term	10 years
Notional Amount	$ 200,000,000
Maturity Date	Nov. 12, 2020
Not Designated as Hedging Instrument | Cash Flow Hedging | American Assets Trust, L.P. | Interest Rate Swap, 3/1/2023 | Wells Fargo Bank, N.A.
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amount								$ 200,000,000
Effective Date								Aug. 11, 2020
Maturity Date								Nov. 12, 2020
Interest rate swap liability								$ (551,000)
Interest Rate Derivative Liabilities, at Fair Value								$ 551,000