Dispositions of Real Estate and Discontinued Operations - Brookedale MTCA Disposition (Details) $ in Thousands	1 Months Ended	3 Months Ended					12 Months Ended
	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) property	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) property	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Nov. 01, 2017 property
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings							$ 335,709	$ 462,242	$ 0
Gain (loss) on sales of real estate, net			$ 95,000	$ 25,000			$ 925,985	$ 356,641	$ 164,698
Senior housing triple-net
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on sales of real estate, net	$ 170,000
Senior housing triple-net | Assets Leased to Others
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets to be sold (in properties) | property										2
SHOP
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on sales of real estate, net					$ 21,000
Brookedale MTCA
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets to be sold (in properties) | property		19					19
Brookedale MTCA | Assets Leased to Others
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings		$ 377,000
Gain (loss) on sales of real estate, net						$ 40,000
Brookedale MTCA | Senior housing triple-net | Assets Leased to Others
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets to be sold (in properties) | property		11					11
Brookedale MTCA | SHOP
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets to be sold (in properties) | property		8					8