Mortgages Payable - Outstanding Mortgages Payable (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023
Mortgage Loans on Real Estate
Notes payable	$ 988,019	$ 1,092,551
Mortgages
Mortgage Loans on Real Estate
Notes payable, gross	996,544	1,096,544
Deferred debt issuance costs, net of accumulated amortization of $7,381 and $17,639, respectively	(8,525)	(3,993)
Deferred debt issuance costs, accumulated amortization	$ 7,381	17,639
Mortgages \| 731 Lexington Avenue \| Office space
Mortgage Loans on Real Estate
Interest rate	5.04%
Notes payable, gross	$ 400,000	500,000
Mortgages \| 731 Lexington Avenue \| Retail space
Mortgage Loans on Real Estate
Interest rate	1.76%
Notes payable, gross	$ 300,000	300,000
Capped rate	1.51%
Swapped fixed rate	1.76%
Mortgages \| Rego Park II \| Retail space
Mortgage Loans on Real Estate
Interest rate	5.60%
Notes payable, gross	$ 202,544	202,544
Mortgages \| Rego Park II \| Retail space \| SOFR
Mortgage Loans on Real Estate
Capped rate	1.45%
Mortgages \| Rego Park II \| Retail space \| Secured Overnight Financing Rate (SOFR) Capped Rate
Mortgage Loans on Real Estate
Capped rate	4.15%
Mortgages \| The Alexander apartment tower \| Apartment Building
Mortgage Loans on Real Estate
Interest rate	2.63%
Notes payable, gross	$ 94,000	$ 94,000

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