Mortgages Payable - Schedule of Long-term Debt Instruments (Details) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2025	Dec. 31, 2024
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Notes payable	$ 987,619	$ 988,019
Mortgages
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Deferred debt issuance costs, accumulated amortization	8,964	7,381
Notes payable, gross	994,561	996,544
Deferred debt issuance costs, net of accumulated amortization of $8,964 and $7,381, respectively	$ (6,942)	(8,525)
Mortgages \| 731 Lexington Avenue
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	5.83%
Mortgages \| 731 Lexington Avenue \| Office Space
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	5.04%
Notes payable, gross	$ 400,000	400,000
Mortgages \| 731 Lexington Avenue \| Retail Space
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	5.83%
Notes payable, gross	$ 300,000	300,000
Basis spread over SOFR	1.51%
Swapped fixed rate	1.76%
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	$ 200,561	202,544
Mortgages \| Rego Park II \| Retail Space \| SOFR
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread over SOFR	1.45%
Mortgages \| Rego Park II \| Retail Space \| SOFR capped rate
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest cap rate	4.15%
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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Amount of accumulated amortization of debt issuance costs.

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

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

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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.

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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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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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