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Mortgages Payable - Additional Information (Detail) - USD ($) $ in Thousands | 9 Months Ended |  |
--- | --- | --- | ---
Sep. 30, 2021 | Apr. 07, 2021 | Dec. 31, 2020
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |
Mortgages payable, net of deferred debt issuance costs | $ 1,157,263 |  | $ 1,156,170
Mortgages |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |
Mortgages payable, net of deferred debt issuance costs | $ 1,157,263 |  | 1,156,170
731 Lexington Avenue | Office Space | Mortgages |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |
Debt instrument, description of variable rate basis | LIBOR |  |
Interest rate (in percentage) | 0.98% |  |
731 Lexington Avenue | Office Space | Mortgages | LIBOR |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |
Basis spread over LIBOR | 0.90% |  |
731 Lexington Avenue | Retail Space | Mortgages |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |
Interest rate (in percentage) | 1.72% |  |
731 Lexington Avenue | Retail Space | Mortgages | Interest Rate Swap |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |
Interest rate (in percentage) | 1.72% |  |
731 Lexington Avenue | Retail Space | Mortgages | LIBOR |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |
Debt instrument, description of variable rate basis | LIBOR |  |
Basis spread over LIBOR | 1.40% |  |
Rego Park II | Retail Space | Mortgages |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |
Debt instrument, description of variable rate basis | LIBOR |  |
Interest rate (in percentage) | 1.43% |  |
Rego Park II | Retail Space | Mortgages | LIBOR |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |
Basis spread over LIBOR | 1.35% |  |
Participation Agreement | Rego Park II | Retail Space | Mortgages |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |
Mortgages payable, net of deferred debt issuance costs |  | $ 202,544 | 252,544
Loan participation balance |  |  | $ 50,000

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