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Summary of Significant Accounting Policies - Investments (Details) |  |  | 12 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Jan. 01, 2020 USD ($) shares | Sep. 30, 2019 | Dec. 31, 2022 USD ($) property shares | Dec. 31, 2021 USD ($) | Dec. 31, 2020 USD ($) | Feb. 28, 2023 $ / shares | Jun. 30, 2022 | Jun. 28, 2022 | Dec. 31, 2019 shares | Mar. 31, 2017
Investment in available for sale securities |  |  |  |  |  |  |  |  |  |
Gains and losses on equity securities, net |  |  | $ 25,660,000 |  |  |  |  |  |  |
Number of medical office and life science properties | property |  |  | 10 |  |  |  |  |  |  |
Subsequent Event | AlerisLife Inc |  |  |  |  |  |  |  |  |  |
Investment in available for sale securities |  |  |  |  |  |  |  |  |  |
Investment in equity securities acquisition, share price (in dollars per share) | $ / shares |  |  |  |  |  | $ 1.31 |  |  |  |
Common stock proposed acquisition percentage |  |  |  |  |  | 31.90% |  |  |  |
AlerisLife Inc |  |  |  |  |  |  |  |  |  |
Investment in available for sale securities |  |  |  |  |  |  |  |  |  |
Investment in common shares (in shares) | shares |  |  | 10,691,658 |  |  |  |  |  |  |
Recurring | AlerisLife Inc | Quoted Prices in Active Markets for Identical Assets (Level 1) | Carrying Amount |  |  |  |  |  |  |  |  |  |
Investment in available for sale securities |  |  |  |  |  |  |  |  |  |
Investment in common shares (in shares) | shares |  |  | 10,691,658 |  |  |  |  |  |  |
Investments in Five Star |  |  | $ 5,880,000 | $ 31,540,000 |  |  |  |  |  |
Gains and losses on equity securities, net |  |  |  | 42,232,000 |  |  |  |  |  |
AlerisLife Inc |  |  |  |  |  |  |  |  |  |
Investment in available for sale securities |  |  |  |  |  |  |  |  |  |
Shares issued, value |  |  | $ 0 | $ 0 | $ 59,801,000 |  |  |  |  |
AlerisLife Inc | Common Shares |  |  |  |  |  |  |  |  |  |
Investment in available for sale securities |  |  |  |  |  |  |  |  |  |
Issued (in shares) | shares | 10,268,158 |  |  |  |  |  |  |  |  |
Shares issued, value | $ 38,095,000 |  |  |  |  |  |  |  |  |
AlerisLife Inc | Common Shares |  |  |  |  |  |  |  |  |  |
Investment in available for sale securities |  |  |  |  |  |  |  |  |  |
Investment in common shares (in shares) | shares |  |  |  |  |  |  |  |  | 423,500 |
Reverse stock split ratio |  | 0.100 |  |  |  |  |  |  |  |
Affiliated Entity | Common Shares | Recurring | AlerisLife Inc |  |  |  |  |  |  |  |  |  |
Investment in available for sale securities |  |  |  |  |  |  |  |  |  |
Investment in common shares (in shares) | shares |  |  | 10,691,658 |  |  |  |  |  |  |
Joint Venture |  |  |  |  |  |  |  |  |  |
Investment in available for sale securities |  |  |  |  |  |  |  |  |  |
Principal amount of debt |  |  | $ 1,076,625,000 |  |  |  |  |  |  |
Seaport Innovation LLC | Joint Venture |  |  |  |  |  |  |  |  |  |
Investment in available for sale securities |  |  |  |  |  |  |  |  |  |
Equity method investment ownership percentage |  |  | 10.00% | 20.00% |  |  | 20.00% | 20.00% |  | 55.00%
Principal amount of debt |  |  | $ 620,000,000 |  |  |  |  |  |  |
LSMD Fund REIT LLC | Joint Venture |  |  |  |  |  |  |  |  |  |
Investment in available for sale securities |  |  |  |  |  |  |  |  |  |
Equity method investment ownership percentage |  |  | 20.00% |  |  |  |  |  |  |
Principal amount of debt |  |  | $ 456,625,000 |  |  |  |  |  |  |

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