Face (par) amount of debt instrument at time of issuance.

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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- Definition

Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

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- Definition

Weighted average yield of investment in debt security measured at amortized cost (held-to-maturity) maturing after tenth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition

Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

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- Definition

The cash inflow from additional borrowings, net of cash paid to third parties in connection with debt origination.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
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- Definition

Amount of cash outflow for payment of an obligation from a lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

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- Definition

The cash outflow to repay long-term debt that is not secured by collateral. Excludes repayments of tax exempt unsecured debt.

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Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

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No definition available.

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Subsequent Events (Details) - USD ($)		12 Months Ended
Subsequent Events (Details) - USD ($)	Jan. 26, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Subsequent Event [Line Items]
Repayment of unsecured line of credit		$ 0	$ 123,000,000	$ 20,000,000
American Assets Trust, L.P.
Subsequent Event [Line Items]
Repayment of unsecured line of credit		$ 0	$ 123,000,000	$ 20,000,000
Senior Guaranteed Notes, Series A \| Unsecured debt \| American Assets Trust, L.P.
Subsequent Event [Line Items]
Stated Interest Rate		4.04%
Subsequent Event [Member]
Subsequent Event [Line Items]
Stated Interest Rate	3.375%
Debt Instrument, Redemption Price, Percentage	98.935%
Debt Securities, Held-to-Maturity, Weighted Average Yield, Maturity, after Year 10	3.502%
Proceeds from Debt, Net of Issuance Costs	$ 489,900,000
Subsequent Event [Member] \| Unsecured debt
Subsequent Event [Line Items]
Face amount of debt	500,000,000
Subsequent Event [Member] \| Senior Guaranteed Notes, Series A \| Unsecured debt \| American Assets Trust, L.P.
Subsequent Event [Line Items]
Repayments of Unsecured Debt	150,000,000.0
Gain (Loss) on Extinguishment of Debt	3,900,000
Subsequent Event [Member] \| Second Amended and Restated Credit Facility \| Unsecured line of credit \| American Assets Trust, L.P.
Subsequent Event [Line Items]
Repayment of unsecured line of credit	$ 100,000,000