Dispositions and Assets Held for Sale - Narrative (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2019 USD ($) property	Dec. 31, 2018 USD ($)	[1]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Real property held for sale	$ 1,704,206	$ 590,271
Held for sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Secured debt	37,429
Net other assets and liabilities	58,816
Net impairment charges	$ 9,939
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	55
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	30
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	4

[1] The consolidated balance sheet at December 31, 2018 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.