Dispositions and Assets Held for Sale - Narrative (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($) property	May 07, 2020 USD ($) property	Dec. 31, 2019 USD ($)	[1]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Real property held for sale	$ 729,560		$ 1,253,008
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 | property	18
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 | property	6
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 | property	9
Held for sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Real property held for sale	$ 729,560
Secured debt	112,625
Net other assets and liabilities	27,800
Net impairment charges	$ 27,827
Subsequent event
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Real property held for sale		$ 412,535
Number of properties no longer held for sale | property		11
Assets no longer held for sale		$ 386,744

[1] The consolidated balance sheet at December 31, 2019 has been derived from the audited financial statements at that date but does not include all of the information and footnotes required by U.S. generally accepted accounting principles for complete financial statements.