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Debt and Preferred Equity Investments (Details) |  | 3 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Dec. 31, 2020 USD ($) property | Sep. 30, 2021 USD ($) property | Dec. 31, 2018 USD ($) | Sep. 03, 2021 USD ($)
Summary of Investment Holdings [Line Items] |  |  |  |
Number of real estate properties | property |  | 81 |  |
Austin Preferred Equity Investment | Notes Receivable |  |  |  |
Summary of Investment Holdings [Line Items] |  |  |  |
Note receivable | $ 50,000,000 |  |  |
Number of real estate properties | property | 2 |  |  |
Notes receivable, interest rate | 9.00% |  |  |
Extension option term | 1 year |  |  |
Note receivable repurchased amount |  |  |  | $ 50,000,000
Gain on financing receivable redemption |  | $ 2,800,000 |  |
Brandywine 1919 Ventures |  |  |  |
Summary of Investment Holdings [Line Items] |  |  |  |
Note receivable |  |  | $ 44,400,000 |
Notes receivable, interest rate |  |  | 4.00% |
Debt, net |  |  | $ 44,400,000 |
Repayment of construction loan |  |  | $ 88,800,000 |

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