Business and Property Management Agreements with RMR LLC (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) employee agreement	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Real Estate Properties [Line Items]
Entity number of employees | employee	0
RMR LLC
Real Estate Properties [Line Items]
Property management fees percentage of gross collected rents	3.00%
Construction supervision fees as percentage of construction costs	5.00%
RMR LLC | Up C Transaction
Real Estate Properties [Line Items]
Recognized amortization of liability		$ 3,585	$ 3,585
RMR LLC | RMR Inc.
Real Estate Properties [Line Items]
Recognized amortization of liability	$ 3,585	3,585	3,585
Amended and restated business management agreement | RMR LLC
Real Estate Properties [Line Items]
Number of management agreements | agreement	2
Base management fee payable as a percentage of average historical cost of the real estate investments, excluding transferred assets for investments up to a specific amount	0.70%
Base management fee payable as percentage of aggregate book value of real estate assets or transferred assets	$ 250,000
Base management fee payable as percentage of average historical cost of real estate investments excluding transferred assets for investments exceeding specified amount	0.50%
Base management fee payable as percentage of average closing stock price on stock exchange	0.70%
Base management fee payable as percentage of average market capitalization exceeding specified amount	0.50%
Incentive fee as percentage of product of weighted average common shares outstanding	12.00%
Incentive fee, consecutive trading days for share price multiplier	10 days
Incentive fee, final trading days of relevant measurement period	30 days
Percentage of shares issued in payment of incentive management fees	1.50%
Business management fees	$ 41,607	39,942	40,694
Incentive fee paid		53,635	74,753
Construction supervision fees	1,399	64	45
Related party reimbursement expense	$ 620	$ 399	$ 482
Amended and restated business management agreement | RMR LLC | Up C Transaction
Real Estate Properties [Line Items]
Window for providing notice of termination of property management agreement for performance by the related party	60 days
Window providing notice of termination of property management agreement after change of control by related party	12 months
Termination fee remaining term assumption	10 years
Period over which transition services will be provided by the related party after termination of the agreement	120 days
Amended and restated business management agreement | RMR LLC | Maximum
Real Estate Properties [Line Items]
Base management fee payable, average market capitalization	$ 250,000
Base management fee payable, threshold amount of other real estate investments	$ 250,000
Incentive management fee reduction	0.0500
Amended and restated business management agreement | RMR LLC | Maximum | Up C Transaction
Real Estate Properties [Line Items]
Termination fee term	20 years
Amended and restated business management agreement | RMR LLC | Minimum
Real Estate Properties [Line Items]
Incentive management fee reduction	0.0200
Amended and restated business management agreement | RMR LLC | Minimum | Up C Transaction
Real Estate Properties [Line Items]
Termination fee term	19 years