Master Transactions and Cooperation Agreement with Brookdale (Details)		1 Months Ended				3 Months Ended					9 Months Ended		12 Months Ended
	Jan. 31, 2020 USD ($) property lease	Jan. 31, 2020 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Nov. 30, 2017 USD ($) property facility	Dec. 31, 2020 property	Sep. 30, 2020 USD ($) property	Jun. 30, 2020 property	Mar. 31, 2020 USD ($) property	Sep. 30, 2019 USD ($) property	Sep. 30, 2020 USD ($) property	Sep. 30, 2019 USD ($) property	Dec. 31, 2019 USD ($) property	Dec. 31, 2018 property	Jan. 31, 2020 facility	Jan. 31, 2020 property	Jan. 31, 2020	Oct. 31, 2019 property	Jan. 01, 2018 USD ($) property
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of properties disposed | property									18
Capital investment							$ 4,000,000				$ 4,000,000
Loss (gain) upon change of control, net											173,222,000	$ 11,481,000
Long-term debt							6,457,117,000				6,457,117,000
Gain (loss) on sales of real estate, net							$ 149,000		$ 165,000,000	$ (784,000)	$ 247,881,000	$ 18,708,000
Payment to acquired noncontrolling interest			$ 63,000,000	$ 32,000,000
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 (loss) on sales of real estate, net	$ 164,000,000
CCRC JV
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Property count | property							2				2
Investment ownership percentage							49.00%				49.00%		49.00%				49.00%
Equity method investments							$ 347,000				$ 347,000		$ 325,830,000
CCRC JV | Brookedale MTCA
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Interest acquired	51.00%
Purchase cost	$ 1,060,000,000.00	$ 1,060,000,000.00
Management termination fee	$ 100,000,000
CCRC JV | Brookedale MTCA | Forecast
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of assets to be sold | property						2
CCRC JV | Brookedale MTCA
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Property count | property																15
Number of properties acquired | property	13
Equity method investments	$ 323,000,000	323,000,000
Real estate and intangible assets	1,800,000,000	1,800,000,000
Refundable entrance fee liabilities	308,000,000	308,000,000
Non-refundable entrance fee liabilities	436,000,000	436,000,000
Long-term debt	215,000,000	215,000,000
Working capital	48,000,000	48,000,000
Cash paid	396,000,000
CCRC JV | Brookedale MTCA | Other Income (Expense)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Loss (gain) upon change of control, net	$ 170,000,000
2019 Amended Master Lease | Brookedale MTCA
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Annual rent escalator	2.40%
RIDEA Facilities
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Ownership percentage (as a percent)					90.00%
Percentage of interest acquired					10.00%
Assets Leased to Others
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of assets transitioned | property														37
Assets Leased to Others | 2019 Amended Master Lease | Brookedale MTCA
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of properties to be restructured | property																24
Number of leases to be terminated | lease	1
Percent of sales proceeds	6.50%
Number of properties to be reallocated | property																14
Future rent	$ 20,000,000	20,000,000
Capital investment	$ 35,000,000	$ 35,000,000
Capital investment term	5 years
Annual percent increase	7.00%
Assets Leased to Others | 2019 Amended Master Lease | Brookedale MTCA | Forecast
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of leases to be terminated | property						1
Assets Leased to Others | RIDEA Facilities
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Property count | facility					58
Other Non-reportable Segments
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of assets to be sold | property							1
Other Non-reportable Segments | Assets Leased to Others | CCRC JV
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Property count															15	15		15
Other Non-reportable Segments | Assets Leased to Others | CCRC JV | Brookedale MTCA
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Property count							13				13				13	13
Interest acquired		51.00%
Senior Housing Triple-Net
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of assets to be sold | property									18			2
Senior Housing Triple-Net | Assets Leased to Others
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Property count | property					78													43
Disposition of properties, available for sale | property					32
Reduction in rent																			$ 5,000,000
Number of properties with rent concessions | property																			3
Total consideration for disposition of real estate					$ 35,000,000
Number of assets transitioned | property														17
Senior Housing Triple-Net | Assets Leased to Others | Brookedale MTCA
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of properties disposed | property					2
SHOP
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of assets to be sold | property							4	2	7	1		11
SHOP | Assets Leased to Others
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of assets transitioned | property														20
SHOP | Assets Leased to Others | Brookedale MTCA
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of assets to be sold | property					4
SHOP | Assets Leased to Others | RIDEA Facilities
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Property count | property					36
Total consideration for disposition of real estate					$ 240,000,000