Related Person Transactions (Details) (USD $) In Thousands, except Share data, unless otherwise specified	1 Months Ended	3 Months Ended		0 Months Ended		3 Months Ended						3 Months Ended	1 Months Ended	3 Months Ended		3 Months Ended	1 Months Ended		1 Months Ended	3 Months Ended
	Jan. 31, 2013	Mar. 31, 2013 item	Mar. 31, 2012	Apr. 16, 2013 Agreement to acquire Senior living communities Cumming, GA item	Mar. 27, 2013 RMR	Mar. 31, 2013 RMR item	Mar. 31, 2012 RMR	Mar. 31, 2013 Five Star item	Mar. 31, 2012 Five Star	Dec. 31, 2012 Five Star	May 31, 2011 Five Star	Mar. 31, 2013 Five Star AL Pooling Agreement item	Aug. 31, 2012 Five Star IL Pooling Agreement item	Mar. 31, 2013 Five Star Senior living communities item	Mar. 31, 2013 Five Star Rehabilitation hospitals item	Mar. 31, 2013 Five Star Acquisition	May 31, 2011 Five Star Acquisition Senior living communities item	Mar. 31, 2013 Five Star Acquisition Senior living communities New York item	Jun. 30, 2012 AIC	Mar. 31, 2013 AIC	Mar. 31, 2012 AIC	Dec. 31, 2012 AIC
Related person transactions
Number of employees		0
Number of agreements to avail management and administrative services						2
Number of Managing Trustees also serving as managing trustee of Five Star								1
Business management agreement expense						$ 6,550	$ 6,360
Common shares issued in payment of an incentive fee for services rendered from RMR					21,968
Common shares issued in public offering	11,500,000
Net proceeds from issuance of common shares issued in public offering	262,068	261,859
Management fees payable under property management agreement as a percentage of gross rents														5.00%
Property management agreement expense						1,600	1,399	2,295	1,068
Beneficial ownership of common shares (as a percent)								100.00%
Investment in common shares								4,235,000
Percentage of total shares outstanding								8.80%
Number of real estate properties leased														188	2
Minimum annual rent payable to entity								198,357
Total rental income recognized								49,444	48,811
Rents receivable								17,620		17,680
Deferred percentage rent								1,254	1,211
Real estate improvements purchased								8,171								8,171
Increase or decrease in annual lease rent payable								654								656
Number of pooling agreement								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
Number of living units				93														310
Aggregate purchase price of properties acquired, excluding closing costs				22,030
Amount agreed to be lent under Bridge Loan Agreement											80,000
Interest and other income		173	482						275
Number of other shareholders in the equity method investee company		5
Ownership percentage held by us, RMR, Five Star, CWH and four other companies																				12.50%
The entity owns less than this percentage of an equity method investment																				20.00%
Number of properties acquired or agreed to be acquired																	6
Amount invested in equity investee																				5,209
Equity method investments, carrying value																				5,697		5,629
Earnings and losses recognized related to equity investments		76	45																	76	45
Period for which property insurance program was extended																			1 year
Coverage of property insurance																				500,000
Total premiums including taxes and fees																			$ 4,438