Dispositions and Assets Held for Sale - Narrative (Details) $ in Thousands	9 Months Ended
	Sep. 30, 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 | $	$ 362,886	$ 1,253,008
Expected proceeds from properties held for sale | $	437,116
Impairment of assets held for sale | $	79,905
Impairment of assets held for use | $	46,386
Held for sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Secured debt | $	12,737
Net other assets and liabilities | $	$ 21,063
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	8
Number of properties subject to asset impairment	13
Number of properties held for use	4
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	2
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	11