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Rego Park II Loan Participation - Additional Information (Detail) - USD ($) $ in Thousands |  | 9 Months Ended
--- | --- | ---
Jul. 28, 2017 | Sep. 30, 2018 | Sep. 30, 2017
Investment In Loan Participation [Line Items] |  |  |
Rego Park II loan participation payment |  | $ 0 | $ 200,000
Participation Agreement | Rego Park II |  |  |
Investment In Loan Participation [Line Items] |  |  |
Loan maturity date | Nov. 30, 2018 |  |
Rego Park II loan participation payment | $ 200,000 |  |
Debt Instrument, Description of Variable Rate Basis | LIBOR |  |
Interest rate (in percentage) |  | 3.86% |
Participation Agreement | Rego Park II | LIBOR |  |  |
Investment In Loan Participation [Line Items] |  |  |
Basis spread over LIBOR | 1.60% |  |

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