Concentration of Credit Risk (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Concentration of Credit Risk
Investment	$ 5,183,307	$ 4,721,591
Revenue	460,811	422,166	340,113
Five Star \| Senior living communities
Concentration of Credit Risk
Number of properties acquired, referred to as managed properties	39
Investment \| Rents from significant lessee
Concentration of Credit Risk
Investment	5,183,307	4,721,591
% of Total (as a percent)	100.00%	100.00%
Investment \| Rents from significant lessee \| Five Star
Concentration of Credit Risk
Investment	2,181,338	2,150,722
% of Total (as a percent)	42.00%	46.00%
Investment \| Rents from significant lessee \| All others
Concentration of Credit Risk
Investment	3,001,969	2,570,869
% of Total (as a percent)	58.00%	54.00%
Rental income \| Rents from significant lessee
Concentration of Credit Risk
Revenue	460,811	422,166
% of Total (as a percent)	100.00%	100.00%
Rental income \| Rents from significant lessee \| Five Star
Concentration of Credit Risk
Revenue	200,912	195,409
% of Total (as a percent)	44.00%	46.00%
Rental income \| Rents from significant lessee \| All others
Concentration of Credit Risk
Revenue	$ 259,899	$ 226,757
% of Total (as a percent)	56.00%	54.00%

Represents the number of properties acquired or agreed to be acquired by the entity during the period, which are referred by the entity as managed properties.

No definition available.

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- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 18

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6351-108592

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 21

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13537-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6404-108592

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13531-108611

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- Definition

Amount of real estate investment property which may include the following: (1) land available-for-sale; (2) land available-for-development; (3) investments in building and building improvements; (4) tenant allowances; (5) developments in-process; (6) rental properties; and (7) other real estate investments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.1(d))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

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- Definition

The aggregate revenue from real estate operations during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1(e))

-URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 5

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