Related Person Transactions (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended		0 Months Ended	3 Months Ended		6 Months Ended		1 Months Ended	3 Months Ended		6 Months Ended				6 Months Ended		1 Months Ended	6 Months Ended		1 Months Ended		1 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2013 item	Jun. 30, 2012	Jun. 30, 2013 item	Jun. 30, 2012	Mar. 27, 2013 RMR	Jun. 30, 2013 RMR item	Jun. 30, 2012 RMR	Jun. 30, 2013 RMR item	Jun. 30, 2012 RMR	Apr. 30, 2012 Five Star	Jun. 30, 2013 Five Star item	Jun. 30, 2012 Five Star	Jun. 30, 2013 Five Star item	Jun. 30, 2012 Five Star	Dec. 31, 2012 Five Star	May 31, 2011 Five Star	Jun. 30, 2013 Five Star AL Pooling Agreement item	Jun. 30, 2013 Five Star Second AL Pooling Agreement item	Aug. 31, 2012 Five Star IL Pooling Agreement item	Jun. 30, 2013 Five Star Senior living communities item	Jun. 30, 2013 Five Star Rehabilitation hospitals item	May 31, 2011 Five Star Acquisition Senior living communities item	Jun. 30, 2013 Five Star Acquisition Senior living communities New York item	Jun. 30, 2013 AIC	Jun. 30, 2013 AIC	Jun. 30, 2012 AIC	Jun. 30, 2013 AIC	Jun. 30, 2012 AIC	Dec. 31, 2012 AIC
Related person transactions
Beneficial ownership of common shares (as a percent)											100.00%		100.00%
Investment in common shares											4,235,000		4,235,000
Percentage of total shares outstanding											8.80%		8.80%
Number of real estate properties leased																				188	2
Minimum annual rent payable to entity													$ 198,984
Total rental income recognized											49,595	48,942	99,027	97,753
Rents receivable											17,804		17,804		17,680
Deferred percentage rent											1,268	1,201	2,517	2,412
Real estate improvements purchased													15,901
Increase or decrease in annual lease rent payable													1,272
Number of pooling agreement											3		3				2
Number of communities that include assisted living units																	20
Number of communities that include independent living units																			2
Number of properties acquired, referred to as managed properties																				39
Property management agreement expense						1,659	1,424	3,259	2,770		2,281	1,080	4,576	2,148
Number of living units																							310
Number of communities under long-term management agreements																		20
Amount agreed to be lent under Bridge Loan Agreement																80,000
Number of employees	0		0
Number of agreements to avail management and administrative services						2		2
Number of Managing Trustees also serving as managing trustee of Five Star											1		1
Business management agreement expense						6,691	6,367	13,241	12,727
Common shares issued in payment of an incentive fee for services rendered from RMR					21,968
Management fees payable under property management agreement as a percentage of gross rents																				5.00%
Interest and other income	397	227	570	709								39		314
Proceeds from repayment of bridge loan										38,000
Number of other shareholders in the equity method investee company	5		5
Ownership percentage held by us, RMR, Five Star, CWH and four other companies																								12.50%	12.50%		12.50%
The entity owns less than this percentage of an equity method investment																								20.00%	20.00%		20.00%
Number of properties acquired or agreed to be acquired																						6
Amount invested in equity investee																								5,209	5,209		5,209
Equity method investments, carrying value																								5,703	5,703		5,703		5,629
Earnings and losses recognized related to equity investments	79	76	155	121																					79	76	155	121
Period for which property insurance program was extended																								1 year
Coverage of property insurance																											500,000
Total premiums including taxes and fees																								4,748
Incentive fee payable																				$ 0