Equity Investments (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended			1 Months Ended	3 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010	Jul. 31, 2011 GOV	Sep. 30, 2011 GOV	Sep. 30, 2010 GOV	Sep. 30, 2011 GOV	Sep. 30, 2010 GOV	Dec. 31, 2010 GOV	Sep. 30, 2011 AIC entity	Sep. 30, 2010 AIC	Sep. 30, 2011 AIC Y entity	Sep. 30, 2010 AIC	Dec. 31, 2010 AIC
Equity Investments
Equity method investments, ownership percentage							21.10%		21.10%		24.60%	14.30%		14.30%		14.30%
Equity investments	$ 178,652		$ 178,652		$ 171,464		$ 173,407		$ 173,407		$ 166,388	$ 5,245		$ 5,245		$ 5,076
Equity investments, common shares owned (in shares)							9,950,000		9,950,000
Equity in earnings (losses) of an investee	2,768	1,999	8,390	6,643			2,740	1,964	8,279	6,660		28	35	111	(17)
Equity investments, quoted market price of common share (in dollars per share)							$ 21.51		$ 21.51		$ 26.79
Common shares issued (in shares)						6,500,000
Common stock price per share (in dollars per share)						$ 25.40
Ownership percentage prior to transaction (as a percent)						24.60%
Ownership percentage after the transaction (as a percent)						21.10%
Recognized gain						11,177
Net proceeds received on issuance of common shares						157,900
Market value of common shares exceeded carrying value							13,824		13,824
Amortizing the difference between carrying value and share of underlying equity (in years)									30Y
Cash distributions									12,438	12,039
Amount invested in equity investee												5,209		5,209
Number of companies to which RMR provides management services												5		5
Period for which property insurance program was extended (in years)														1
Premium for property insurance														5,540		5,328
Amount expensed in relation to insurance premiums												$ 1,385	$ 1,332	$ 4,067	$ 1,776