Period when adjustments to the carrying value of an interest-bearing hedged item are amortized upon discontinuation of the fair value hedge, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Fixed interest rate related to the interest rate derivative.

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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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DERIVATIVE AND HEDGING ACTIVITIES (Details) - USD ($)							9 Months Ended
DERIVATIVE AND HEDGING ACTIVITIES (Details) - USD ($)	Jul. 17, 2019	Jun. 20, 2019	May 11, 2017	Jan. 18, 2017	Sep. 19, 2014	Aug. 19, 2014	Sep. 30, 2019
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							$ (1,674,000)
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							$ (180,000)
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							$ (62,000)
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