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Related Party Transactions and Investments in Non-Consolidated Entities - Management fees and interest income from loans (Details) - USD ($) | 6 Months Ended
--- | ---
Jun. 30, 2019 | Jun. 30, 2018
Schedule of Equity Method Investments [Line Items] |  |
Asset management fees, low end of range (as a percent) | 1.00% |
Asset management fees, high end of range (as a percent) | 5.00% |
Notice period for cancellation of applicable contracts | 30 days |
Revenue | $ 118,000 | $ 271,000
Revenue, Product and Service [Extensible List] | us-gaap:AssetManagement1Member | us-gaap:AssetManagement1Member
Sponsored REITs |  |
Schedule of Equity Method Investments [Line Items] |  |
Impairment of Sponsored REIT | $ 0 |

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