Business and Property Management Agreements with RMR LLC - Net Business Management Fees (Details) - RMR LLC $ in Thousands	1 Months Ended	3 Months Ended
	Jan. 31, 2017 USD ($)	Mar. 31, 2017 USD ($) agreement	Mar. 31, 2016 USD ($)
Amended and restate business management agreement
Real Estate Properties [Line Items]
Number of management service agreements | agreement		2
Business management fees incurred		$ 29,770	$ 13,781
Estimated incentive fees recorded		19,620	5,316
Incentive fees paid	$ 52,407
Related party property management and construction management fee		10	14
Related party reimbursement expenses		46	38
Internal audit expense
Real Estate Properties [Line Items]
Related party costs and expenses		$ 67	$ 67