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Business and Property Management Agreements with RMR LLC (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2021 USD ($) agreement employee	Mar. 31, 2020 USD ($)	Dec. 31, 2020
Related person transactions
Number of employees | employee	0
Property management and construction supervision fees	$ 3,154,000	$ 3,192,000
Property management and construction supervision fees paid	3,297,000	3,443,000
RMR LLC
Related person transactions
Business management fees incurred	5,317,000	5,769,000
Related party transaction business management fees related to subsidiary level management	725,000
Related party transaction business management agreement, annual incentive fee estimate included in management fees	0	0
Period of actual amount of incentive fees			3 years
Property management and construction supervision fees	2,485,000	2,596,000
Party transaction property management and construction supervision fees capitalized	$ 669,000	$ 596,000
Senior Living Communities | Five Star
Related person transactions
Number of consecutive renewal terms of agreement | agreement	2

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