Dispositions and Real Property Held for Sale (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) property	Dec. 31, 2019 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Real property held for sale | $	$ 216,613	$ 1,253,008
Impairment of assets held for sale | $	87,873
Impairment of assets held for use | $	47,735
Held For Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Secured debt | $	276,363
Net other assets and liabilities | $	$ 35,811
Seniors Housing Operating
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties classified as held for sale	4
Number of properties subject to asset impairment	15
Number of properties held for use	6
Triple-net
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties classified as held for sale	1
Number of properties subject to asset impairment	1
Number of properties held for use	4
Outpatient Medical
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties classified as held for sale	10