Dispositions of Real Estate and Discontinued Operations - Assets and Liabilities for Discontinued Operations (Details)	Dec. 31, 2021 USD ($) property	Dec. 31, 2020 USD ($) property	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Real estate:
Cash and cash equivalents	$ 7,707,000	$ 53,085,000	$ 63,834,000	$ 56,811,000
Restricted cash	0	17,168,000	$ 27,040,000	$ 21,890,000
Intangible assets, net	0	25,000,000
Total assets of discontinued operations, net	37,190,000	2,626,306,000
LIABILITIES
Total liabilities of discontinued operations, net	15,056,000	415,737,000
Allowance for doubtful accounts receivable	4,138,000	5,873,000
Goodwill	18,000,000	18,000,000
Right-of-use asset, net	233,942,000	192,349,000
Deferred revenue	789,207,000	774,316,000
Held-for-sale
Real estate:
Buildings and improvements	0	2,553,254,000
Development costs and construction in progress	0	21,509,000
Land	0	355,803,000
Accumulated depreciation and amortization	0	(615,708,000)
Net real estate	0	2,314,858,000
Investments in and advances to unconsolidated joint ventures	0	5,842,000
Accounts receivable, net of allowance of $4,138 and $5,873	2,446,000	20,500,000
Cash and cash equivalents	7,707,000	53,085,000
Restricted cash	0	17,168,000
Intangible assets, net	0	24,541,000
Right-of-use asset, net	26,000	4,109,000
Other assets, net	3,237,000	103,965,000
Total assets of discontinued operations, net	13,416,000	2,544,068,000
Assets held for sale, net	23,774,000	82,238,000
Assets held for sale and discontinued operations, net	37,190,000	2,626,306,000
LIABILITIES
Mortgage debt	0	318,876,000
Lease liability	26,000	3,189,000
Accounts payable, accrued liabilities, and other liabilities	14,843,000	79,411,000
Deferred revenue	92,000	11,442,000
Total liabilities of discontinued operations, net	14,961,000	412,918,000
Liabilities related to assets held for sale, net	95,000	2,819,000
Liabilities related to assets held for sale and discontinued operations, net	15,056,000	415,737,000
Goodwill	0	29,000,000
Net real estate assets	23,000,000	73,000,000
Right-of-use asset, net	$ 1,000,000
Deferred revenue		$ 2,000,000
Held-for-sale | Senior Housing Operating Portfolio
LIABILITIES
Number of properties classified as held for sale | property	0	97
Held-for-sale | Senior Housing Triple Net
LIABILITIES
Number of properties classified as held for sale | property	0	41
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	6
Held-for-sale | Life science
LIABILITIES
Number of properties classified as held for sale | property	1