Dispositions of Real Estate and Discontinued Operations - Assets and Liabilities for Discontinued Operations (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Real estate:
Cash and cash equivalents	$ 40,161	$ 53,085	$ 66,791	$ 63,834
Restricted cash	5,817	17,168	$ 21,576	$ 27,040
Intangible assets, net	9,000	25,000
Total assets of discontinued operations, net	1,374,507	2,626,306
LIABILITIES
Total liabilities of discontinued operations, net	328,167	415,737
Allowance for doubtful accounts receivable	5,132	5,873
Deferred revenue	765,946	774,316
Held-for-sale
Real estate:
Buildings and improvements	1,174,263	2,553,254
Development costs and construction in progress	11,136	21,509
Land	201,699	355,803
Accumulated depreciation and amortization	(221,246)	(615,708)
Net real estate	1,165,852	2,314,858
Investments in and advances to unconsolidated joint ventures	5,776	5,842
Accounts receivable, net of allowance of $5,132 and $5,873	13,976	20,500
Cash and cash equivalents	40,161	53,085
Restricted cash	5,817	17,168
Intangible assets, net	8,539	24,541
Right-of-use asset, net	937	4,109
Other assets, net(1)	43,224	103,965
Total assets of discontinued operations, net	1,284,282	2,544,068
Total medical office assets held for sale, net	90,225	82,238
Assets held for sale and discontinued operations, net	1,374,507	2,626,306
LIABILITIES
Mortgage debt	278,172	318,876
Lease liability	935	3,189
Accounts payable, accrued liabilities, and other liabilities	41,977	79,411
Deferred revenue	3,985	11,442
Total liabilities of discontinued operations, net	325,069	412,918
Total liabilities related to medical office assets held for sale, net	3,098	2,819
Liabilities related to assets held for sale and discontinued operations, net	328,167	415,737
Goodwill	29,000	29,000
Net real estate assets	81,000	73,000
Deferred revenue	$ 2,000	$ 2,000