Dispositions of Real Estate and Discontinued Operations - 2020 Dispositions of Real Estate (Details) $ in Thousands		1 Months Ended		3 Months Ended	12 Months Ended
	Jan. 31, 2020 USD ($) property	Jan. 31, 2021 USD ($) property	Dec. 31, 2020 USD ($) property	Mar. 31, 2021 USD ($)	Dec. 31, 2021 USD ($) property	Dec. 31, 2020 USD ($) property	Dec. 31, 2019 USD ($) property
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Repayments of secured debt			$ 6,000
Number of assets classified as discontinued operations | property			1			1
Gain (loss) on sales of real estate, net					$ 190,590	$ 90,350	$ (40)
Net cash provided by (used in) financing activities					(1,288,517)	246,450	647,271
Disposal Group, Disposed of by Means Other than Sale, Not Discontinued Operations, Abandonment
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on sales of real estate, net							30,000
Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on sales of real estate, net							23,000
Brookedale MTCA
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on sales of real estate, net	$ 164,000
Number of properties disposed | property	18
Other Investments | Disposal Group, Disposed of by Means Other than Sale, Not Discontinued Operations, Abandonment
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on sales of real estate, net					58,000	283,000
Other Investments | Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on sales of real estate, net					39,000	$ 193,000
Other Investments | Brookedale MTCA
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties disposed | property						18
Senior Housing Triple Net
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings							26,000
Senior Housing Triple Net | Aegis NNN Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings			$ 358,000
Gain (loss) on sales of real estate, net			$ 228,000
Senior Housing Triple Net | Other Investments
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets sold | property						21
Proceeds from sale of buildings					24,000	$ 428,000
Atria SHOP Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets sold | property			12
Senior Housing Operating Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings		$ 230,000					181,000
Gain (loss) on sales of real estate, net		59,000		$ 16,000
Net cash provided by (used in) financing activities		$ 150,000
Senior Housing Operating Portfolio | Atria SHOP Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets sold | property			12
Proceeds from sale of buildings			$ 312,000
Gain (loss) on sales of real estate, net			$ 39,000
Senior Housing Operating Portfolio | Other Investments
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings					$ 169,000	190,000
Medical Office
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings							$ 28,000
Medical Office | Other Investments
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings						136,000
MOB Land Parcels | Other Investments
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings						$ 3,000
Senior Housing Triple Net
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets sold | property							2
Senior Housing Triple Net | Aegis NNN Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets sold | property			10
Senior Housing Triple Net | Other Investments
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets sold | property					7
Senior Housing Operating Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets sold | property		16					18
Senior Housing Operating Portfolio | Atria SHOP Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets sold | property			4
Proceeds from sale of buildings			$ 94,000
Net cash provided by (used in) financing activities			$ 61,000
Senior Housing Operating Portfolio | Other Investments
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets sold | property					15	23
Medical Office
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets sold | property							11
Medical Office | Other Investments
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets sold | property					10	11
Proceeds from sale of buildings					$ 68,000
Medical Office | Other Investments | San Diego
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets sold | property						3
MOB Land Parcels | Other Investments
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets sold | property					1	2
Other Non-Reporting Segment | Other Investments
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets sold | property						1
Proceeds from sale of buildings						$ 1,000