Business and Property Management Agreements with RMR LLC - (Details)		5 Months Ended	12 Months Ended
	Jun. 05, 2015	Jun. 05, 2015 shares	Dec. 31, 2016 USD ($) employee day	Dec. 31, 2016 USD ($) employee day	Dec. 31, 2016 USD ($) employee lease_agreement day	Dec. 31, 2016 USD ($) employee day management_agreement	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($) shares
Related Party Transaction [Line Items]
Number of employees | employee			0	0	0	0
Property management and construction supervision fees				$ 10,585,000			$ 10,342,000	$ 8,259,000
Property management and construction supervision fees paid				9,061,000			7,021,000	5,289,000
Professional Fees				235,000			256,000	278,000
RMR LLC
Related Party Transaction [Line Items]
Business management fees incurred				36,763,000			34,949,000	$ 30,794,000
Recognized amortization of the liability				2,974,000			1,743,000
Common shares issued for the incentive fees | shares		68,983						123,462
Related Party Transaction Business Management Agreement Incentive Fee Payable			$ 0	$ 0	$ 0	$ 0	$ 0	$ 0
Period over which transition services will be provided by the related party after termination of the agreement			120 days
MOBs | RMR LLC
Related Party Transaction [Line Items]
Base business management fee payable in cash (as a percent)			3.00%	3.00%	3.00%	3.00%
Construction supervision fees payable under property management agreement as a percentage of construction costs			5.00%	5.00%	5.00%	5.00%
Senior Living Communities | Five Star
Related Party Transaction [Line Items]
Number of consecutive renewal terms of agreement					2	2
Amended Agreement
Related Party Transaction [Line Items]
Base management fee payable as a percentage of aggregate book value of real estate assets or transferred assets			0.50%	0.50%	0.50%	0.50%
Amended Agreement | RMR LLC
Related Party Transaction [Line Items]
Base management fee payable as a percentage of average historical cost of real estate investments, excluding transferred assets for investments exceeding specified amount			0.50%	0.50%	0.50%	0.50%
Base management fee payable as a percentage of average historical cost of real estate investments, excluding transferred assets for investments up to specified amount			0.70%	0.70%	0.70%	0.70%
Threshold amount of other real estate investments for payment of base management fee			$ 250,000,000	$ 250,000,000	$ 250,000,000	$ 250,000,000
Base management fee payable as a percentage of average market capitalization exceeding specified amount			0.50%	0.50%	0.50%	0.50%
Threshold amount of average market capitalization for payment of base management fee			$ 250,000,000	$ 250,000,000	$ 250,000,000	$ 250,000,000
Base management fee payable as a percentage of average closing price per share of common shares on NYSE			0.70%	0.70%	0.70%	0.70%
Incentive management fee payable (as a percent)			12.00%	12.00%	12.00%	12.00%
Period of measurement			3 years
Period applicable in the case of calculation of the incentive management fee for 2015			2 years
Shorter period applicable in the case of calculation of the incentive management fee for 2014			1 year
Related Party Transaction, Incentive Management Fee Cap on Common Shares			1.50%	1.50%	1.50%	1.50%
Related Party Transaction, Incentive Management Fee, Top Consecutive Trading Days | day			10	10	10	10
Related Party Transaction, Incentive Management Fee, Consecutive Trading Days | day			30	30	30	30
Amended Agreement | RMR LLC | Up C Transaction
Related Party Transaction [Line Items]
Number of business days notice for termination of property management agreement for convenience by the related party	60 days
Window for providing notice of termination of property management agreement for performance by the related party	60 days
Window for providing notice of termination of property management agreement for change of control by the related party	12 months
Number of terminated management agreements for convenience before termination fee is incurred | lease_agreement					1
Number of RMR LLC terminated management agreements for good cause before termination fee is incurred | lease_agreement					1
Number of terminated management agreements for a performance reason before termination fee is incurred | lease_agreement					1
Termination fee remaining term assumption			10 years
Maximum | RMR LLC
Related Party Transaction [Line Items]
Threshold amount of real estate investments for payment of base management fee			$ 250,000,000	$ 250,000,000	$ 250,000,000	$ 250,000,000
Base management fee payable, average market capitalization			$ 250,000,000	$ 250,000,000	$ 250,000,000	$ 250,000,000
Maximum | Amended Agreement | RMR LLC | Up C Transaction
Related Party Transaction [Line Items]
Termination fee term			20 years
Minimum | Amended Agreement | RMR LLC | Up C Transaction
Related Party Transaction [Line Items]
Termination fee term			19 years