Dispositions, Assets Held for Sale and Discontinued Operations (Details) $ in Thousands	3 Months Ended
Mar. 31, 2018 USD ($) properties	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
Real property dispositions:
Total dispositions	$ 548,936	$ 822,049
Gain (loss) on sale of properties	338,184	244,092
Net other assets/liabilities disposed	5,089	20,933
Proceeds from sales of real property	892,209	1,087,074
Net Real Estate Investments	25,941,125		$ 26,171,077
Asset Impairment Charges	28,185	11,031
Triple Net [Member]
Real property dispositions:
Total dispositions	$ 323,667	808,204
Number of properties classified as held for sale \| properties	36
Asset Impairment Charges	$ 25,884	0
Senior housing - operating [Member]
Real property dispositions:
Total dispositions	$ 2,200	13,845
Number of properties classified as held for sale \| properties	7
Asset Impairment Charges	$ 2,301	5,406
Outpatient Medical [Member]
Real property dispositions:
Total dispositions	$ 223,069	0
Number of properties classified as held for sale \| properties	2
Asset Impairment Charges	$ 0	$ 5,625
Held for sale
Real property dispositions:
Net Real Estate Investments	$ 368,249

Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=68055307&loc=d3e2420-110228

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

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The difference between the carrying value and the sale price of real estate or properties that were intended to be sold or held for capital appreciation or rental income. This element refers to the gain (loss) included in earnings and not to the cash proceeds of the sale. This element is a noncash adjustment to net income when calculating net cash generated by operating activities using the indirect method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

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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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Amount of real estate investments, net of accumulated depreciation, 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; (7) other real estate investments; (8) real estate joint ventures; and (9) unconsolidated real estate and other joint ventures not separately presented.

+ 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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Gain Loss On Sale Of Other Assets and Liabilities.

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

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Real property dispositions.

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Real property dispositions.

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