Business and Property Management Agreements with RMR LLC (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2019 USD ($)	Dec. 31, 2019 USD ($) employee agreement	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Related Party Transaction [Line Items]
Recognized amortization of the liability			$ 603	$ 603
Incentive management fee			0	0
Transaction amount			484	484
RMR LLC
Related Party Transaction [Line Items]
Number of employees | employee		0
Number of agreements with RMR LLC to provide management services | agreement		2
Net business management fees			16,381	12,464
Recognized amortization of the liability		$ 603
Management fees as percentage of gross collected rents		3.00%
Construction supervision fees as percentage of construction costs		5.00%
Reimbursement amounts	$ 462	$ 26,442	21,279	15,321
RMR LLC | Net Property Management and Construction Supervision Fees
Related Party Transaction [Line Items]
Net business management fees		21,320
Transaction amount		21,911	$ 13,989	$ 11,566
Reimbursement amounts		$ 484
RMR LLC | Transition Services
Related Party Transaction [Line Items]
Duration of transition services		120 days
Amended And Restate Business Management Agreement | RMR LLC
Related Party Transaction [Line Items]
Percentage applied on average historical cost of real estate investment properties acquired		0.50%
Base management fee payable as percentage of average historical cost of real estate investments		0.70%
Percentage of average closing stock price on stock exchange		0.70%
Management fee payable as percentage of average market capitalization exceeding specified amount		0.50%
Percentage for limitation and adjustments of incentive management fee payable		12.00%
Measurement period for incentive management fee		3 years
Percentage for limitation and adjustments of incentive management fee payable, minimum total return per share percentage change		5.00%
Average closing price of our common shares, consecutive trading days		10 days
Highest Average closing price of our common shares, final consecutive trading days		30 days
Percentage of base business management fee payable in common shares		1.50%
Amended And Restate Business Management Agreement | RMR LLC | Up C Transaction
Related Party Transaction [Line Items]
Written notice for convenience		60 days
Window of written notice after calendar year		60 days
Window for written notice after change of control		12 months
Remaining termination fee term		10 years
Minimum | Amended And Restate Business Management Agreement | RMR LLC
Related Party Transaction [Line Items]
Threshold amount of average market capitalization		$ 250,000
Percentage for limitation and adjustments of incentive management fee payable, total return per share percentage, reduction		2.00%
Minimum | Amended And Restate Business Management Agreement | RMR LLC | Up C Transaction
Related Party Transaction [Line Items]
Termination fee term		19 years
Maximum | Amended And Restate Business Management Agreement | RMR LLC
Related Party Transaction [Line Items]
Threshold amount of real estate investments		$ 250,000
Base management fee payable average market capitalization		$ 250,000
Percentage for limitation and adjustments of incentive management fee payable, total return per share percentage, reduction		5.00%
Maximum | Amended And Restate Business Management Agreement | RMR LLC | Up C Transaction
Related Party Transaction [Line Items]
Termination fee term		20 years
RMR LLC
Related Party Transaction [Line Items]
Incentive management fee		$ 0
SIR | RMR LLC | Net Property Management and Construction Supervision Fees
Related Party Transaction [Line Items]
Transaction amount		2,185
SIR | RMR LLC | Business Management Incentive Fee
Related Party Transaction [Line Items]
Transaction amount		$ 25,817