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Mortgages Payable - Summary of Outstanding Mortgages Payable Narrative (Detail) - Mortgages - USD ($) $ in Thousands |  | 9 Months Ended |
--- | --- | --- | ---
Oct. 03, 2018 | Sep. 30, 2018 | Dec. 31, 2017
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |
Deferred debt issuance costs, accumulated amortization |  | $ 10,219 | $ 6,315
Paramus |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |
Maturity date |  | Oct. 05, 2018 |
Retail Space | Rego Park I |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |
Percentage of cash mortgage collateralized |  | 100.00% |
Refinance date |  | May 11, 2018 |
Repayment date |  | Jun. 06, 2018 |
Retail Space | Rego Park II |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |
Maturity date |  | Nov. 30, 2018 |
Retail Space | 731 Lexington Avenue |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |
Maturity date |  | Aug. 01, 2022 |
Subsequent Event | Paramus |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |
Maturity date | Oct. 04, 2021 |  |

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