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Debt and Preferred Equity Investments - Narrative (Details) | 3 Months Ended | 9 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | ---
Sep. 30, 2021 USD ($) investment | Mar. 31, 2021 segment | Sep. 30, 2020 USD ($) | Sep. 30, 2021 USD ($) segment investment | Sep. 30, 2020 USD ($) | Dec. 31, 2020 USD ($) investment | Dec. 31, 2019 USD ($) | Aug. 31, 2018 receivable
Preferred equity investment |  |  |  |  |  |  |  |
Number of investments, nonperforming | investment | 1 |  |  | 1 |  | 1 |  |
Debt and preferred equity investments | $ 1,052,110,000 |  |  | $ 1,052,110,000 |  | $ 1,076,542,000 |  |
Recorded investment, past due | 1,052,110,000 |  |  | 1,052,110,000 |  | 1,076,542,000 |  |
Recorded investment, nonaccrual status | 27,700,000 |  |  | $ 27,700,000 |  | 27,700,000 |  |
Number of portfolio segments of financial receivables (segment) | segment |  | 1 |  | 1 |  |  |  |
Additional amount of financing receivables included in other assets | 50,300,000 |  |  | $ 50,300,000 |  | 66,200,000 |  |
Current period provision for loan loss | 0 |  | $ 0 | 0 | $ 6,300,000 | 20,693,000 |  |
Allowance for loan and lease losses, real estate | 6,630,000 |  |  | 6,630,000 |  | 13,213,000 | $ 1,750,000 |
3 - High Risk Assets - Loss more likely than not |  |  |  |  |  |  |  |
Preferred equity investment |  |  |  |  |  |  |  |
Recorded investment, past due | 6,890,000 |  |  | 6,890,000 |  | 16,340,000 |  |
Recorded investment, nonaccrual status | 2,500,000 |  |  | 2,500,000 |  |  |  |
Number of receivables put on nonaccrual | receivable |  |  |  |  |  |  |  | 1
Financing Receivables, Equal to Greater than 90 Days Past Due |  |  |  |  |  |  |  |
Preferred equity investment |  |  |  |  |  |  |  |
Recorded investment, past due | 0 |  |  | 0 |  | 0 |  |
Cumulative Effect, Period of Adoption, Adjustment |  |  |  |  |  |  |  |
Preferred equity investment |  |  |  |  |  |  |  |
Allowance for loan and lease losses, real estate |  |  |  |  |  | 0 | $ 27,803,000 |
Total floating rate |  |  |  |  |  |  |  |
Preferred equity investment |  |  |  |  |  |  |  |
Debt and preferred equity investments | 281,495,000 |  |  | 281,495,000 |  | 352,460,000 |  |
Total floating rate | Mortgage/Mezzanine Loan Due March 2020 |  |  |  |  |  |  |  |
Preferred equity investment |  |  |  |  |  |  |  |
Debt and preferred equity investments | $ 6,800,000 |  |  | $ 6,800,000 |  | $ 6,800,000 |  |

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