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Shareholders' Equity (Details)				1 Months Ended				12 Months Ended
	Dec. 14, 2015 USD ($) $ / shares	Sep. 24, 2015 $ / shares shares	Jun. 05, 2015 shares	May. 31, 2015 trustee	Feb. 28, 2015 USD ($) shares	Apr. 30, 2014 USD ($) shares	Jan. 31, 2013 USD ($) shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) trustee $ / shares	Dec. 31, 2013 USD ($) $ / shares
Distributions
Distribution to common shareholders (in dollars per share) | $ / shares								$ 1.56	$ 1.56	$ 1.56
Distribution to common shareholders | $								$ 356,390,000	$ 305,767,000	$ 288,945,000
Common shares issued in public offering					31,050,000	15,525,000	11,500,000
Net proceeds after underwriting discounts from issuance of common shares issued in public offering | $					$ 659,496,000	$ 322,807,000	$ 261,813,000	$ 659,496,000	$ 322,807,000	$ 261,813,000
D - Common Stock Dividends, Ordinary Income Distribution Percentage								51.48%	54.00%	66.19%
D - Common Stock Dividends, Return of Capital Distribution Percentage								47.80%	46.00%	21.30%
D - Common Stock Dividends, Capital Gain Distribution Percentage								0.00%	0.00%	3.10%
D - Common Stock Dividends, Unrecaptured Section 1250 Gain Distribution Percentage								0.00%	0.00%	9.41%
Number of trustees | trustee				5					5
RMR LLC
Distributions
Distribution to common shareholders (in dollars per share) | $ / shares	$ 0.0111
Distribution to common shareholders | $	$ 2,635,379
Shares issued in connection with acquisition								81,557
Certain Our Officers And Employees Of RMR LLC
Distributions
Shares purchased from certain of our officers and other employees of RMR LLC		13,113
Closing share price of the entity's common shares (in dollars per share) | $ / shares		$ 16.19
RMR LLC
Distributions
Shares issued in connection with acquisition			2,345,000

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