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Mortgages Payable - Summary of Outstanding Mortgages Payable (Detail) - USD ($) $ in Thousands | 9 Months Ended |  |  |
--- | --- | --- | --- | ---
Sep. 30, 2020 | Sep. 14, 2020 | Sep. 13, 2020 | Dec. 31, 2019
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |  |
Notes payable | $ 1,066,403 |  |  | $ 970,961
Mortgages |  |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |  |
Mortgage payable gross | 1,070,544 |  |  | 974,836
Deferred debt issuance costs, net of accumulated amortization of $12,701 and $14,362, respectively | (4,141) |  |  | (3,875)
Notes payable | 1,066,403 |  |  | 970,961
Deferred debt issuance costs, accumulated amortization | $ 12,701 |  |  | 14,362
Mortgages | Paramus |  |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |  |
Maturity date | Oct. 04, 2021 |  |  |
Interest rate (in percentage) | 4.72% |  |  |
Mortgage payable gross | $ 68,000 |  |  | 68,000
Mortgages | 731 Lexington Avenue | Retail Space |  |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |  |
Maturity date | Aug. 05, 2025 |  |  |
Interest rate (in percentage) | 1.56% |  |  |
Mortgage payable gross | $ 300,000 | $ 300,000 | $ 350,000 | 350,000
Mortgages | 731 Lexington Avenue | Office Space |  |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |  |
Maturity date | Jun. 11, 2024 |  |  |
Interest rate (in percentage) | 1.05% |  |  |
Mortgage payable gross | $ 500,000 |  |  | 500,000
Mortgages | Rego Park II | Retail Space |  |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |  |
Maturity date | Dec. 12, 2025 |  |  |
Interest rate (in percentage) | 1.50% |  |  |
Mortgage payable gross | $ 202,544 |  |  | $ 56,836

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