Dispositions and Assets Held for Sale (Summary of Real Property Disposition Activity) (Details) $ in Thousands	12 Months Ended
Dec. 31, 2018 USD ($) properties	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) portfolio
Summary of real property disposition activity
Real estate classified as held for sale	$ 590,271	$ 734,147
Real property dispositions:
Total dispositions	1,125,117	1,011,218	$ 1,852,400
Gain (loss) on sales of real property, net	415,575	344,250	364,046
Net other assets (liabilities) disposed	1,178	22,546	133,622
Proceeds from real property sales	$ 1,541,870	1,378,014	2,350,068
Seniors Housing Operating
Summary of real property disposition activity
Number of properties classified as held for sale \| properties	13
Real property dispositions:
Total dispositions	$ 36,627	74,832	0
Triple-net
Summary of real property disposition activity
Number of properties classified as held for sale \| properties	40
Real property dispositions:
Total dispositions	$ 835,093	916,689	1,773,614
Proceeds from real property sales	$ 1,541,870	1,378,014	2,350,068
Outpatient Medical
Summary of real property disposition activity
Number of properties classified as held for sale \| properties	2
Real property dispositions:
Total dispositions	$ 253,397	$ 19,697	$ 78,786
Genesis HealthCare
Real property dispositions:
Number of portfolio dispositions of properties leased \| portfolio			2,000
Loans received for termination fees			$ 74,445
Principal outstanding on the loans received for termination fees	$ 61,994

The net gain (loss) resulting from sales and other disposals of real estate owned for investment purposes.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.14(d))
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

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The cash inflow from the sale of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3179-108585

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Carrying amount as of the balance sheet date of investments in land and buildings held for sale, excluding real estate considered to be inventory of the entity.

+ 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(f))
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Revenue from the sale of commercial, industrial, or residential property during the period. This element is more likely than not relevant to an entity for which real estate operations are a principal activity. If real estate operations are not a principal activity, the reporting entity would likely use a gain (loss) on sale of property, plant, or equipment type element.

+ 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))
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Gain Loss On Sale Of Other Assets and Liabilities.

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Amount before allowance of commercial loans received for termination fees related to properties sold.

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Number Of Portfolios Disposed

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This represents the number of the properties which are classified as held for sale.

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This is the outstanding principal of the loans received for termination fees relating to the properties sold under the master lease.

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Real property dispositions.

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Summary of real property disposition activity.

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