Impairments (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2019 USD ($)	Dec. 31, 2020 USD ($) property	Dec. 31, 2019 USD ($) property	Dec. 31, 2018 USD ($) property
Impaired Long-Lived Assets Held and Used [Line Items]
Impairments and loan loss reserves (recoveries), net		$ 42,909	$ 17,708	$ 10,917
Number of real estate properties impaired | property			3
Asset impairment charge			$ 18,000
Casualty related gain			5,000
Other Operating Income (Expense) [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Casualty related gain			2,000
Discontinued Operations
Impaired Long-Lived Assets Held and Used [Line Items]
Impairments and loan loss reserves (recoveries), net		201,000
Asset impairment charge			9,000
Casualty related gain			$ 3,000
Senior Housing Triple Net, SHOP, And MOB [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Impairments and loan loss reserves (recoveries), net		$ 210,000
Senior Housing Operating Portfolio
Impaired Long-Lived Assets Held and Used [Line Items]
Impairments and loan loss reserves (recoveries), net	$ 10,000
Number of real estate properties impaired | property		42	27	17
Number of real estate properties impaired, candidates for potential sale | property			1
Senior Housing Operating Portfolio | Held-for-sale
Impaired Long-Lived Assets Held and Used [Line Items]
Number of properties classified as held for sale | property		97	115
Senior Housing Operating Portfolio | Underperformed assets
Impaired Long-Lived Assets Held and Used [Line Items]
Number of real estate properties impaired | property				3
Senior Housing Triple Net
Impaired Long-Lived Assets Held and Used [Line Items]
Number of real estate properties impaired | property		5	8
Senior Housing Triple Net | Held-for-sale
Impaired Long-Lived Assets Held and Used [Line Items]
Number of properties classified as held for sale | property		41	90
Medical Office
Impaired Long-Lived Assets Held and Used [Line Items]
Impairments and loan loss reserves (recoveries), net			$ 4,000
Number of real estate properties impaired | property		5	3
Number of properties intended to be demolished | property			1
Number of real estate properties impaired, candidates for potential sale | property			2
Medical Office | Held-for-sale
Impaired Long-Lived Assets Held and Used [Line Items]
Number of properties classified as held for sale | property		6	2
MOB Land Parcels
Impaired Long-Lived Assets Held and Used [Line Items]
Number of real estate properties impaired | property		1
Life Science
Impaired Long-Lived Assets Held and Used [Line Items]
Impairments and loan loss reserves (recoveries), net		$ 15,000
Number of properties intended to be demolished | property		1
Life Science | Held-for-sale
Impaired Long-Lived Assets Held and Used [Line Items]
Number of properties classified as held for sale | property				1
Senior Housing Triple Net, SHOP, MOB, and Other Non-Reportable
Impaired Long-Lived Assets Held and Used [Line Items]
Impairments and loan loss reserves (recoveries), net			$ 194,000
Senior Housing Triple Net, SHOP, MOB, and Other Non-Reportable | Discontinued Operations
Impaired Long-Lived Assets Held and Used [Line Items]
Impairments and loan loss reserves (recoveries), net			$ 189,000
Other Non-Reporting Segment
Impaired Long-Lived Assets Held and Used [Line Items]
Number of real estate properties impaired | property			1
Senior Housing Operating Portfolio And Undeveloped Life Science
Impaired Long-Lived Assets Held and Used [Line Items]
Impairments and loan loss reserves (recoveries), net				$ 52,000
Senior Housing Operating Portfolio And Undeveloped Life Science | Discontinued Operations
Impaired Long-Lived Assets Held and Used [Line Items]
Impairments and loan loss reserves (recoveries), net				$ 44,000
Shop Assets, Senior Housing Triple-net Assets, MOBs, and Other Non-Reportable Asset
Impaired Long-Lived Assets Held and Used [Line Items]
Aggregate carrying value before impairment		$ 960,000	$ 416,000
Real estate held-for-sale		750,000	223,000
Minimum
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment calculation price range		$ 13	$ 24
Market capitalization rate			4.97%
Terminal capitalization rate		5.50%
Discount rates		8.00%
Maximum
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment calculation price range		$ 300	$ 125
Market capitalization rate			8.27%
Terminal capitalization rate		7.50%
Discount rates		9.50%
Weighted Average
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment calculation price range		$ 164	$ 73
Market capitalization rate			6.22%