Dispositions of Real Estate and Discontinued Operations - Assets and Liabilities for Discontinued Operations (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021 USD ($) property	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) property loan	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) property	Dec. 31, 2019 USD ($)
Real estate:
Cash and cash equivalents	$ 17,354	$ 58,879	$ 17,354	$ 58,879	$ 53,085	$ 63,834
Restricted cash	974	20,211	974	20,211	17,168	$ 27,040
Intangible assets, net	7,000		7,000		25,000
Total assets of discontinued operations, net	246,807		246,807		2,626,306
LIABILITIES
Total liabilities of discontinued operations, net(2)	65,272		65,272		415,737
Allowance for doubtful accounts receivable	4,951		4,951		5,873
Right-of-use asset	215,303		215,303		192,349
Financing receivable, after allowance for credit loss	429,076		429,076		195,375
Deferred revenue	777,687		777,687		774,316
Mortgage Debt
LIABILITIES
Debt instrument, periodic payment	1,000	1,000	3,000	2,000
Held-for-sale
Real estate:
Buildings and improvements	106,495		106,495		2,553,254
Development costs and construction in progress	11,255		11,255		21,509
Land	24,215		24,215		355,803
Accumulated depreciation and amortization	(42,999)		(42,999)		(615,708)
Net real estate	98,966		98,966		2,314,858
Investments in and advances to unconsolidated joint ventures	0		0		5,842
Accounts receivable, net of allowance of $4,951 and $5,873	10,928		10,928		20,500
Cash and cash equivalents	17,354		17,354		53,085
Restricted cash	974		974		17,168
Intangible assets, net	6,596		6,596		24,541
Right-of-use asset, net	104		104		4,109
Other assets, net	29,908		29,908		103,965
Total assets of discontinued operations, net	164,830		164,830		2,544,068
Assets held for sale, net	81,977		81,977		82,238
Assets held for sale and discontinued operations, net	246,807		246,807		2,626,306
LIABILITIES
Mortgage debt(4)	37,069		37,069		318,876
Lease liability	104		104		3,189
Accounts payable, accrued liabilities, and other liabilities	26,564		26,564		79,411
Deferred revenue	797		797		11,442
Total liabilities of discontinued operations, net(2)	64,534		64,534		412,918
Liabilities related to assets held for sale, net	738		738		2,819
Liabilities related to assets held for sale and discontinued operations, net	65,272		65,272		415,737
Goodwill	22,000		22,000		29,000
Net real estate assets	26,000		26,000		73,000
Right-of-use asset	3,000		$ 3,000
Number of loans receivable | loan			2
Financing receivable, after allowance for credit loss	$ 53,000		$ 53,000
Deferred revenue					$ 2,000
Held-for-sale | Senior housing triple-net
LIABILITIES
Number of properties classified as held for sale | property	4		4		41
Held-for-sale | SHOP
LIABILITIES
Number of properties classified as held for sale | property	8		8		97
Held-for-sale | Senior Housing Operating Portfolio Joint Venture
LIABILITIES
Number of properties classified as held for sale | property					1
Held-for-sale | Medical office
LIABILITIES
Number of properties classified as held for sale | property	4		4		6
Discontinued Operations | Mortgage Debt
LIABILITIES
Debt instrument, periodic payment	$ 241,000	$ 1,000	$ 281,000	$ 6,000