Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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=84177426&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 20
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13531-108611

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=84177426&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 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13537-108611

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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

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- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ 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)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

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Leases and Management Agreements with Five Star - Schedule of Assets Leased and Revenues Earned (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Concentration Risk [Line Items]
Carrying Value of Investment	$ 7,824,763				$ 7,617,547				$ 7,824,763	$ 7,617,547
Revenues	278,566	$ 266,679	$ 265,013	$ 264,561	274,296	$ 263,983	$ 261,367	$ 258,375	1,074,819	1,058,022	$ 998,773
Real Estate Investment Property At Cost \| Rents from significant lessee
Concentration Risk [Line Items]
Carrying Value of Investment	8,474,950				8,251,964				$ 8,474,950	$ 8,251,964
Concentration of credit risk (as a percent)									100.00%	100.00%
Sales Revenue, Services, Net \| Rents from significant lessee
Concentration Risk [Line Items]
Revenues									$ 1,074,819	$ 1,058,022
Concentration of credit risk (as a percent)									100.00%	100.00%
Five Star \| Real Estate Investment Property At Cost \| Rents from significant lessee
Concentration Risk [Line Items]
Carrying Value of Investment	2,330,630				2,290,029				$ 2,330,630	$ 2,290,029
Concentration of credit risk (as a percent)									27.50%	27.80%
Five Star \| Sales Revenue, Services, Net \| Rents from significant lessee
Concentration Risk [Line Items]
Revenues									$ 210,539	$ 203,581
Concentration of credit risk (as a percent)									19.60%	19.20%
All others \| Real Estate Investment Property At Cost \| Rents from significant lessee
Concentration Risk [Line Items]
Carrying Value of Investment	$ 6,144,320				$ 5,961,935				$ 6,144,320	$ 5,961,935
Concentration of credit risk (as a percent)									72.50%	72.20%
All others \| Sales Revenue, Services, Net \| Rents from significant lessee
Concentration Risk [Line Items]
Revenues									$ 864,280	$ 854,441
Concentration of credit risk (as a percent)									80.40%	80.80%