Related Person Transactions (Details 2) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended			1 Months Ended	12 Months Ended	1 Months Ended	12 Months Ended					12 Months Ended		1 Months Ended	12 Months Ended					12 Months Ended			1 Months Ended		3 Months Ended	12 Months Ended		1 Months Ended
	Dec. 31, 2011 trustee sqft	Dec. 31, 2010 sqft	Dec. 31, 2009 sqft	Feb. 29, 2012 SIR property sqft	Dec. 31, 2011 SIR trustee	Feb. 29, 2012 SIR Suburban office and industrial properties property	Dec. 31, 2011 Sale sqft property	Dec. 31, 2011 GOV	Dec. 31, 2010 GOV	Dec. 31, 2009 GOV	Feb. 22, 2012 GOV	Dec. 31, 2011 GOV Sale	Dec. 31, 2010 GOV Sale	Jun. 30, 2010 GOV Agreement to sell property sqft	Dec. 31, 2011 AIC	Dec. 31, 2010 AIC	Dec. 31, 2009 AIC	Feb. 22, 2012 AIC	Jun. 30, 2010 AIC	Dec. 31, 2011 SNH	Dec. 31, 1999 SNH	Feb. 22, 2012 SNH	Sep. 30, 2011 SNH Sale sqft property state	Jan. 31, 2011 SNH Sale property sqft	Jan. 31, 2011 SNH Sale sqft	Dec. 31, 2010 SNH Sale sqft property	Dec. 31, 2009 SNH Sale	Nov. 30, 2010 SNH Agreement to sell property	May 31, 2008 SNH Agreement to sell property
Related person transactions
Percentage of ownership interest of entity in related party								10.00%												10.00%
Amount invested in equity investee																		$ 5,209
Ownership interest in subsidiary before spin-off (as a percent)								100.00%													100.00%
Number of properties sold or agreed to be sold				251		23	20							15									13	6		21		27	47
Aggregate sale price of properties sold or agreed to be sold, excluding closing costs							265,145						231,000										167,000	95,870		374,130		470,000	562,000
Number of maximum additional buildings, rights of first refusal to purchase																													45
Gain (loss) on sale of properties		34,336										0	34,336										7,846	35,000	168,272	133,272	79,133
Number of states in which properties were sold																							8
Deferred gain on sale of properties													14,588
Common shares consideration received on transfer of properties				22,000,000
Non-interest bearing demand promissory note				400,000
Credit facility to be entered by subsidiary				500,000
Number of common managing trustees	2				2
Percentage of ownership interest of entity, RMR,SNH,GOV,HPT,FiveStar and TA											21.10%				14.30%
Property square feet	72,283,000	65,711,000	62,339,000	21,400,000			2,148,000							1,900,000									1,310,000	737,000	2,803,000	2,066,000
Equity investments, common shares owned											9,950,000											250,000
Equity in earnings of investees	11,377	8,464	6,546						8,465	6,679					139	(1)	(133)
Coverage amount for property insurance																			500,000
Premium for property insurance															$ 6,697	$ 5,328