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Summary of Significant Accounting Policies - Investments (Details) |  |  | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | ---
Jan. 01, 2020 USD ($) shares | Dec. 31, 2019 shares | Dec. 31, 2021 USD ($) shares | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) shares | Dec. 23, 2021 | Jun. 30, 2019 shares | Mar. 31, 2017
Investment in available for sale securities |  |  |  |  |  |  |  |
Gains and losses on equity securities, net | $ |  |  | $ (42,232,000) | $ 34,106,000 | $ (41,898,000) |  |  |
ALR |  |  |  |  |  |  |  |
Investment in available for sale securities |  |  |  |  |  |  |  |
Shares issued, value | $ |  |  | $ 0 | $ 59,801,000 | $ 0 |  |  |
ALR | Common Shares |  |  |  |  |  |  |  |
Investment in available for sale securities |  |  |  |  |  |  |  |
Issued (in shares) | shares | 10,268,158 |  |  |  |  |  |  |
Shares issued, value | $ | $ 38,095,000 |  |  |  |  |  |  |
ALR | Common Shares |  |  |  |  |  |  |  |
Investment in available for sale securities |  |  |  |  |  |  |  |
Investment in common shares (in shares) | shares |  | 423,500 |  |  | 423,500 |  |  |
Reverse stock split ratio |  | 0.100 |  |  |  |  |  |
Affiliated Entity | Common Shares | Recurring | ALR |  |  |  |  |  |  |  |
Investment in available for sale securities |  |  |  |  |  |  |  |
Investment in common shares (in shares) | shares |  |  | 10,691,658 |  |  |  |  |
RMR Inc. | Class A common shares |  |  |  |  |  |  |  |
Investment in available for sale securities |  |  |  |  |  |  |  |
Equity investments shares held (in shares) | shares |  |  |  |  |  |  | 2,637,408 |
Seaport Innovation LLC | Joint Venture |  |  |  |  |  |  |  |
Investment in available for sale securities |  |  |  |  |  |  |  |
Equity method investment ownership percentage |  |  | 20.00% |  |  | 20.00% |  | 55.00%
Principal amount of debt | $ |  |  | $ 620,000,000 |  |  |  |  |

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