Shareholders' Equity (Details) - USD ($)			1 Months Ended				12 Months Ended
	Feb. 21, 2017	Jun. 05, 2015	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Feb. 28, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jan. 13, 2017
Distributions
Share-based compensation expense							$ 2,195,000	$ 1,373,000	$ 1,914,000
Distribution to common shareholders (in dollars per share)							$ 1.56	$ 1.56	$ 1.56
Dividends paid in kind				$ 0.1320
Distribution to common shareholders							$ 370,489,000	$ 356,390,000	$ 305,767,000
Common shares issued in public offering						31,050,000
Net proceeds after underwriting discounts from issuance of common shares issued in public offering						$ 659,496,000	$ 0	$ 659,496,000	$ 322,807,000
Common stock dividends, ordinary income distribution percentage							58.77%	51.48%	54.00%
Common stock dividends, capital distribution percentage							40.67%	47.80%	46.00%
Common stock dividends, capital gain distribution percentage							0.56%	0.72%	0.00%
RMR LLC
Distributions
Shares issued in connection with acquisition								81,557
Distribution to common shareholders (in dollars per share)				$ 0.0111
Distribution to common shareholders				$ 2,635,379
Certain Our Officers And Employees Of RMR LLC
Distributions
Shares purchased from certain of our officers and other employees of RMR LLC			19,230		13,113
RMR LLC
Distributions
Shares issued in connection with acquisition		2,345,000
Share Award Plans
Distributions
Number of shares granted under the award plan							92,150	99,000	94,200
Subsequent Event
Distributions
Distribution to common shareholders (in dollars per share)	$ 0.39
Distribution declared to common shareholders (in dollars per share)										$ 0.39
Distribution declared to common shareholders										$ 92,642,000
Dividends paid	$ 92,642,000