Business and Property Management Agreements with RMR LLC (Details) - RMR LLC - USD ($) $ in Thousands	1 Months Ended			12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
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%
Shares issued under management agreement (in shares)					63,119	119,664
Amended and restate business management agreement
Real Estate Properties [Line Items]
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%
Percentage of shares issued in payment of incentive management fees				1.50%
Incentive fee, consecutive trading days for share price multiplier				10 days
Incentive fee, final trading days of relevant measurement period				30 days
Period of measurement				3 years	2 years	1 year
Business management fees				$ 36,802	$ 37,331	$ 37,509
Incentive fee paid		$ 62,263
Shares issued under management agreement (in shares)			102,536
Amount of annual percentage rent waived				64	33	41
Related party reimbursement expense				171	134	75
Amended and restate business management agreement | 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
Internal audit expense
Real Estate Properties [Line Items]
Management agreement, Internal audit cost				235	254	$ 281
Up C Transaction
Real Estate Properties [Line Items]
Recognized amortization of liability				$ 3,585	$ 2,038
Up C Transaction | Amended and restate business management agreement
Real Estate Properties [Line Items]
Management agreement written termination period				60 days
Number of business days notice for termination of property management agreement for performance 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 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
Up C Transaction | Amended and restate business management agreement | Minimum
Real Estate Properties [Line Items]
Termination fee term				19 years
Up C Transaction | Amended and restate business management agreement | Maximum
Real Estate Properties [Line Items]
Termination fee term				20 years
Subsequent event | Amended and restate business management agreement
Real Estate Properties [Line Items]
Incentive fee paid	$ 52,407