Mortgages Payable - Summary of Outstanding Mortgages Payable (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2023	Dec. 31, 2022
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Notes Payable (in US dollars)	$ 1,091,438	$ 1,091,051
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 $16,458 and $16,071, respectively	(5,106)	(5,493)
Notes Payable (in US dollars)	1,091,438	1,091,051
Deferred debt issuance costs, accumulated amortization	$ 16,458	16,071
Mortgages \| 731 Lexington Avenue \| Office Space
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	5.58%
Notes payable, gross	$ 500,000	500,000
Mortgages \| 731 Lexington Avenue \| Office Space \| LIBOR
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread over LIBOR or SOFR	0.90%
Mortgages \| 731 Lexington Avenue \| Office Space \| LIBOR \| Maximum
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 \| Office Space \| Prime Rate
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	8.00%
Extension period	1 year
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
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]
Basis spread over LIBOR or SOFR	1.45%
Mortgages \| Rego Park II \| Retail Space \| Secured Overnight Financing Rate (SOFR) \| Maximum
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 \| Retail Space
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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