Master Transactions and Cooperation Agreement with Brookdale (Details)		1 Months Ended			3 Months Ended			9 Months Ended		12 Months Ended
	Jan. 31, 2020 USD ($) property lease	May 31, 2021 USD ($) property	Dec. 31, 2020 USD ($) property	Oct. 31, 2019 USD ($) property	Sep. 30, 2021 USD ($) property	Sep. 30, 2020 USD ($) property	Mar. 31, 2020 USD ($) property	Sep. 30, 2021 USD ($) property	Sep. 30, 2020 USD ($) property	Dec. 31, 2020 USD ($) property	Jan. 31, 2021 property
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Property count | property	15
Number of properties acquired | property								0
Number of properties disposed | property									18
Capital investment			$ 5,000,000							$ 5,000,000
Gain upon change of control, net								$ 1,042,000	$ 173,222,000
Long-term debt					$ 5,538,404,000			5,538,404,000
Gain on sales of real estate, net					$ 14,635,000	$ 2,283,000		$ 189,873,000	85,636,000
Measurement Input, Discount Rate | Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Measurement input	0.10
Measurement Input, Discount Rate | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Measurement input	0.12
Measurement Input, Annual Rent Escalators | Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Measurement input	0.02
Measurement Input, Annual Rent Escalators | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Measurement input	0.03
Measurement Input, Cap Rate | Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Measurement input	0.07
Measurement Input, Cap Rate | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Measurement input	0.09
Brookedale MTCA
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of properties disposed | property	18									18
Cash proceeds	$ 385,000,000
Gain on sales of real estate, net	$ 164,000,000
CCRC JV
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Property count | property					0			0
Investment ownership percentage	49.00%	49.00%	49.00%							49.00%
Equity method investments			$ 1,581,000		$ 0			$ 0		$ 1,581,000
Proceeds from sale of buildings		$ 19,000,000
CCRC JV | Brookedale MTCA
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Interest acquired	51.00%
Purchase cost	$ 1,060,000,000.00
Management termination fee	$ 100,000,000
Number of assets to be sold | property		2
Proceeds from sale of buildings		$ 38,000,000
CCRC JV | Brookedale MTCA
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Property count | property	15
Number of properties acquired | property	13						13
Equity method investments	$ 323,000,000
Real estate and intangible assets							$ 1,800,000,000
Refundable entrance fee liabilities							308,000,000
Non-refundable entrance fee liabilities							436,000,000
Long-term debt							215,000,000
Working capital							48,000,000
Cash paid							$ 396,000,000
CCRC JV | Brookedale MTCA | Government grant income recorded in other income (expense), net
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Gain upon change of control, net	$ 170,000,000
Senior Housing Triple-Net
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of assets to be sold | property										21
Proceeds from sale of buildings					$ 12,000,000			$ 24,000,000	$ 385,000,000	$ 428,000,000
2019 Amended Master Lease | Brookedale MTCA
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Annual rent escalator percentage	2.40%
Lessor Asset Under Operating Lease | 2019 Amended Master Lease | Brookedale MTCA
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of properties to be restructured | property	24										24
Number of leases to be terminated	1		1
Percent of sales proceeds	6.50%
Number of properties to be reallocated | property	14
Future rent	$ 20,000,000
Capital investment				$ 35,000,000
Capital investment term				5 years
Annual percent increase				7.00%
Other Non-reportable Segments
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of assets to be sold | property						1			1	1
Proceeds from sale of buildings						$ 1,000,000			$ 1,000,000	$ 1,000,000
Other Non-reportable Segments | Lessor Asset Under Operating Lease
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Property count | property			1							1
Other Non-reportable Segments | Lessor Asset Under Operating Lease | Brookedale MTCA
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Property count | property	13
Other Non-reportable Segments | Lessor Asset Under Operating Lease | CCRC JV
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Property count | property				15
Other Non-reportable Segments | Lessor Asset Under Operating Lease | CCRC JV | Brookedale MTCA
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Property count | property	13
Senior Housing Triple-Net
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of assets to be sold | property					4			7	18
Senior Housing Triple-Net | Lessor Asset Under Operating Lease
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Property count | property				43