Mortgages Payable (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2024	Dec. 31, 2023
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Notes Payable (in US dollars)	$ 1,092,952	$ 1,092,551
Mortgages
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Notes payable, gross	1,096,544	1,096,544
Deferred debt issuance costs, net of accumulated amortization of $18,040 and $17,639, respectively	(3,592)	(3,993)
Notes Payable (in US dollars)	1,092,952	1,092,551
Deferred debt issuance costs, accumulated amortization	$ 18,040	17,639
Mortgages \| 731 Lexington Avenue \| Office Space
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	6.00%
Notes payable, gross	$ 500,000	500,000
Mortgages \| 731 Lexington Avenue \| Office Space \| Prime Rate
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest cap rate	6.00%
Mortgages \| 731 Lexington Avenue \| Retail Space
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	1.76%
Notes payable, gross	$ 300,000	300,000
Swapped fixed rate	1.76%
Mortgages \| 731 Lexington Avenue \| Retail Space \| Secured Overnight Financing Rate (SOFR)
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread over LIBOR or SOFR	1.51%
Mortgages \| Rego Park II \| Retail Space
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	5.60%
Notes payable, gross	$ 202,544	202,544
Mortgages \| Rego Park II \| Retail Space \| Secured Overnight Financing Rate (SOFR)
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest cap rate	4.15%
Basis spread over LIBOR or SOFR	1.45%
Mortgages \| The Alexander apartment tower \| Apartment tower
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	2.63%
Notes payable, gross	$ 94,000	$ 94,000

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- References

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-SubTopic 310
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Amount of accumulated amortization of debt issuance costs.

+ References

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- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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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

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Fixed interest rate that will be received or paid upon exercise of the interest rate swaption contract.

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- Definition

Including the current and noncurrent portions, aggregate carrying amount of all types of notes payable, as of the balance sheet date, with initial maturities beyond one year or beyond the normal operating cycle, if longer.

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