Payments For Derivative Instrument

No definition available.

Name:	alx_PaymentsForDerivativeInstrument
Namespace Prefix:	alx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Nominal or face amount used to calculate payments on the derivative asset.

+ References

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+ Details

Name:	us-gaap_DerivativeAssetNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

The percentage points added to the reference rate to compute the variable rate on the interest rate derivative.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeBasisSpreadOnVariableRate
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Cap rate on an interest rate derivative such as an interest rate cap or collar. If market rates exceed the cap rate, a payment or receipt is triggered on the contract.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fixed interest rate related to the interest rate derivative.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeFixedInterestRate
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
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- Details

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- Details

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- Details

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Namespace Prefix:
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- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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Fair Value Measurements - Schedule of Interest Rate Derivatives (Details) - USD ($) $ in Thousands	1 Months Ended
	Jun. 30, 2023	Dec. 31, 2023	Jul. 15, 2023	Dec. 31, 2022
Fair Value Measurements
Included in other assets		$ 22,608		$ 29,351
731 Lexington Avenue
Fair Value Measurements
Payments for derivative instrument	$ 11,258
LIBOR \| 731 Lexington Avenue \| Mortgages
Fair Value Measurements
Interest cap rate			6.00%
Prime Rate \| 731 Lexington Avenue \| Mortgages
Fair Value Measurements
Interest cap rate	6.00%
731 Lexington Avenue mortgage loan, retail condominium \| Interest rate derivatives (included in other assets) \| Designated as Hedging Instrument
Fair Value Measurements
Included in other assets		16,315		26,718
Notional Amount		$ 300,000
Swapped Rate		1.76%
Rego Park II shopping center mortgage loan \| Interest rate derivatives (included in other assets) \| Designated as Hedging Instrument
Fair Value Measurements
Included in other assets		$ 1,370		2,622
Notional Amount		$ 202,544
Rego Park II shopping center mortgage loan \| Interest Rate Contract \| Designated as Hedging Instrument \| SOFR
Fair Value Measurements
Interest cap rate		4.15%
731 Lexington Avenue mortgage loan, office condominium \| Interest rate derivatives (included in other assets) \| Designated as Hedging Instrument
Fair Value Measurements
Included in other assets		$ 4,923		$ 11
Notional Amount		$ 500,000
731 Lexington Avenue mortgage loan, office condominium \| Interest Rate Contract \| Designated as Hedging Instrument \| Prime Rate
Fair Value Measurements
Interest rate		8.50%