Business and Property Management Agreements with RMR LLC (Details) $ in Thousands	1 Months Ended	3 Months Ended
	Jan. 31, 2018 USD ($)	Mar. 31, 2018 USD ($) employee agreement	Mar. 31, 2017 USD ($)
Real Estate Properties [Line Items]
Number of employees | employee		0
RMR LLC | Internal audit expense
Real Estate Properties [Line Items]
Related party costs and expenses		$ 69	$ 67
RMR LLC | Amended and restate business management agreement
Real Estate Properties [Line Items]
Number of management service agreements | agreement		2
Business management fees incurred		$ 9,724	29,770
Estimated incentive fees recorded			19,620
Related Party Transaction, Estimated Incentive Fee Calculation Period		3 years
Incentive fees paid	$ 74,573
Related party property management and construction management fee		$ 13	10
Related party reimbursement expenses		$ 66	$ 46