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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