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Rego Park II Loan Participation - (Narrative) (Details) - USD ($) $ in Thousands |  | 12 Months Ended
--- | --- | ---
Jul. 28, 2017 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Investment In Loan Participation [Line Items] |  |  |  |
Loan participation payment |  | $ 200,000 | $ 0 | $ 0
Participation Agreement | Rego Park II |  |  |  |
Investment In Loan Participation [Line Items] |  |  |  |
Loan participation payment | $ 200,000 |  |  |
Interest rate |  | 3.17% |  |
LIBOR | Participation Agreement | Rego Park II |  |  |  |
Investment In Loan Participation [Line Items] |  |  |  |
Basis spread over LIBOR | 1.60% |  |  |

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