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Debt and Preferred Equity Investments - Rollforward of Net Book Balance (Details) - USD ($) $ in Thousands | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2021 | Dec. 31, 2020
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward] |  |
Balance at beginning of period | $ 1,076,542 | $ 1,580,306
Redemptions/Sales/Syndications/Equity Ownership/Amortization | (145,196) | (1,048,643)
Net change in loan loss reserves | 6,583 | (11,463)
Balance at end of period | 1,052,110 | 1,076,542
Debt Investments in Mortgage Loans |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward] |  |
Originations/Accretion | 104,358 | 389,300
Preferred equity investments |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward] |  |
Originations/Accretion | $ 9,823 | $ 167,042

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- Definition SEC Schedule, 12-29, Real Estate Companies, Investment In Mortgage Loans On Real Estate, Loan Loss Reserve Period Increase (Decrease) + References No definition available. + Details
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- Definition Amount of investment in mortgage loan on real estate by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 948 -SubTopic 310 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-29(Column G)) -URI http://asc.fasb.org/extlink&oid=120402547&loc=d3e617274-123014 + Details
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- Definition Amount of decrease in investment in mortgage loan on real estate by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate, from amortization of premium. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 948 -SubTopic 310 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-29(Footnote 6)) -URI http://asc.fasb.org/extlink&oid=120402547&loc=d3e617274-123014 + Details
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- Definition Amount of increase in mortgage loan on real estate by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate, from new investment. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 948 -SubTopic 310 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-29(Footnote 6)) -URI http://asc.fasb.org/extlink&oid=120402547&loc=d3e617274-123014 + Details
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