Loans Receivable - Narrative (Details)	1 Months Ended							3 Months Ended				6 Months Ended		12 Months Ended
	Jul. 31, 2021 USD ($)	Jun. 30, 2021 USD ($) property	May 31, 2021 USD ($) property	Apr. 30, 2021 USD ($) property	Jan. 31, 2021 USD ($) property	Dec. 31, 2020 USD ($) property	Nov. 30, 2020 USD ($) property	Jun. 30, 2021 USD ($) property	Mar. 31, 2021 USD ($)	Jun. 30, 2020 USD ($) property	Mar. 31, 2020 USD ($)	Jun. 30, 2021 USD ($) property	Jun. 30, 2020 USD ($) property	Dec. 31, 2020 USD ($) property	Jan. 31, 2020 USD ($) property	Dec. 31, 2019 USD ($)	Oct. 31, 2019 property
Loans Receivable:
Net cash provided by financing activities												$ (2,009,272,000)	$ 867,584,000
Reduction of gain on sale of real estate								$ (175,238,000)		$ (81,284,000)		(175,238,000)	(83,353,000)
Gain (loss) on sales of real estate, net								$ 175,238,000		81,284,000		$ 175,238,000	83,353,000
Number of loans held for sale | property		2						2				2
Financing receivable, after allowance for credit loss		$ 429,076,000				$ 195,375,000		$ 429,076,000				$ 429,076,000		$ 195,375,000
Reserves for loans receivable		4,198,000				10,280,000		4,198,000				4,198,000		10,280,000		$ 0
Loss on sale of financing receivable											$ (42,000,000)
Property count | property															15
Credit loss reserve on unfunded loan commitments		200,000				1,000,000		200,000				200,000		1,000,000
Credit loss expenses								1,000,000		$ 5,000,000		4,000,000	$ 13,000,000
Sunrise Senior Housing Portfolio | SHOP
Loans Receivable:
Net cash provided by financing activities					$ 410,000,000
Capital expenditure funding, amount committed		56,000,000			$ 92,000,000
Capital expenditure funding, cost of capital, percent committed					65.00%
Capital expenditure funding, amount funded												0
Secured Loans
Loans Receivable:
Reserves for loans receivable		4,183,000				3,152,000		4,183,000				4,183,000		3,152,000		$ 0
Secured mortgage loans
Loans Receivable:
Financing receivable, gross		$ 416,729,000				$ 161,530,000		$ 416,729,000				$ 416,729,000		$ 161,530,000
SHOP
Loans Receivable:
Number of assets to be sold | property					16			6		2		1	9	23
Proceeds from sale of buildings												$ 5,000,000
SHOP | Sunrise Senior Housing Portfolio
Loans Receivable:
Number of assets to be sold | property		2			32
Proceeds from sale of buildings					$ 664,000,000
Net cash provided by financing activities					410,000,000
Proceeds from the collection of loans receivable		$ 246,000,000
Reduction of gain on sale of real estate		7,000,000
Gain (loss) on sales of real estate, net		$ (7,000,000)
SHOP | Atria SHOP Portfolio
Loans Receivable:
Number of assets to be sold | property						4
Net cash provided by financing activities						$ 61,000,000
SHOP | Discovery SHOP Portfolio
Loans Receivable:
Number of assets to be sold | property				10
Reduction of gain on sale of real estate				$ 0
Gain (loss) on sales of real estate, net				$ 0
SHOP | Atria SHOP Portfolio
Loans Receivable:
Number of assets to be sold | property						4
Proceeds from sale of buildings						$ 94,000,000
Net cash provided by financing activities						$ 61,000,000
SHOP | Secured Loans | Discovery SHOP Portfolio
Loans Receivable:
Number of loans held for sale | property				2
Loss on sale of financing receivable				$ 0
Other non-reportable
Loans Receivable:
Number of assets to be sold | property														1
Proceeds from sale of buildings														$ 1,000,000
Secured Loans
Loans Receivable:
Number of loans held for sale | property							1
Financing receivable, gross							$ 10,000,000
Loss on sale of financing receivable							2,000,000
Proceeds from sale of receivables							$ 8,000,000
Secured mortgage loans
Loans Receivable:
Number of loans held for sale | property		2				1		2				2		1
Financing receivable, gross		$ 64,000,000				$ 115,000,000		$ 64,000,000				$ 64,000,000		$ 115,000,000
Decrease in financing receivable												11,000,000
Financing receivable, after allowance for credit loss		53,000,000						53,000,000				53,000,000
Reserves for loans receivable		8,000,000						8,000,000				8,000,000
Loss on sale of financing receivable						6,000,000		3,000,000				3,000,000
Proceeds from sale of receivables						$ 109,000,000
Principal repayments received			$ 10,000,000
Number of loans receivable | property			1
Secured mortgage loans | Subsequent Event
Loans Receivable:
Principal repayments received	$ 8,000,000
Brookedale MTCA
Loans Receivable:
Reduction of gain on sale of real estate					(164,000,000)
Gain (loss) on sales of real estate, net					164,000,000
Lessor Asset Under Operating Lease | Other non-reportable
Loans Receivable:
Property count | property						1								1
Lessor Asset Under Operating Lease | Brookedale MTCA | Other non-reportable
Loans Receivable:
Property count | property															13
SHOP
Loans Receivable:
Proceeds from sale of buildings					230,000,000			44,000,000		$ 28,000,000			$ 64,000,000	$ 190,000,000
Net cash provided by financing activities					150,000,000
Reduction of gain on sale of real estate					(59,000,000)				$ 16,000,000			(7,000,000)
Loans receivable, market rate									5.25%
Non-cash interest income								9,000,000		$ 0		10,000,000	$ 0
Gain (loss) on sales of real estate, net					$ 59,000,000				$ (16,000,000)			7,000,000
SHOP | Minimum
Loans Receivable:
Loans receivable, stated interest rate									3.50%
Interest income, amortization period									1 year
SHOP | Maximum
Loans Receivable:
Loans receivable, stated interest rate									4.50%
Interest income, amortization period									3 years
SHOP | Atria SHOP Portfolio
Loans Receivable:
Number of assets to be sold | property						12
Proceeds from sale of buildings						$ 312,000,000
Reduction of gain on sale of real estate						(39,000,000)
Gain (loss) on sales of real estate, net						39,000,000
SHOP | Discovery SHOP Portfolio
Loans Receivable:
Proceeds from sale of buildings				334,000,000
Reduction of gain on sale of real estate				(9,000,000)
Gain (loss) on sales of real estate, net				$ 9,000,000
CCRC JV | Brookedale MTCA
Loans Receivable:
Property count | property															15
CCRC JV | Lessor Asset Under Operating Lease | Other non-reportable
Loans Receivable:
Property count | property																	15
CCRC JV | Lessor Asset Under Operating Lease | Brookedale MTCA | Other non-reportable
Loans Receivable:
Financing receivable, after allowance for credit loss		$ 22,000,000				$ 23,000,000		$ 22,000,000				$ 22,000,000		$ 23,000,000	$ 30,000,000
Property count | property															13