Real Estate Transactions - 2019 Dispositions (Details)	1 Months Ended		3 Months Ended							12 Months Ended
	Mar. 31, 2017 USD ($)	Jan. 31, 2017 USD ($)	Dec. 31, 2019 USD ($) property	Sep. 30, 2019 USD ($) property	Jun. 30, 2019 USD ($) property	Mar. 31, 2019 USD ($) property	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) property	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Real Estate [Line Items]
Proceeds from sale of buildings										$ 0	$ 335,709,000	$ 462,242,000
Gain (loss) on sales of real estate, net			$ 11,000,000	$ 0	$ 11,000,000	$ 8,000,000	$ 95,000,000	$ 25,000,000		$ 22,900,000	$ 925,985,000	356,641,000
SHOP
Real Estate [Line Items]
Number of assets to be sold (in properties) | property			7	1	1	9				7
Gain (loss) on sales of real estate, net									$ 21,000,000
Senior housing triple-net
Real Estate [Line Items]
Number of assets to be sold (in properties) | property						2
Gain (loss) on sales of real estate, net	$ 170,000,000
Life science
Real Estate [Line Items]
Number of assets to be sold (in properties) | property					1	1
Gain (loss) on sales of real estate, net		$ 45,000,000
Medical office
Real Estate [Line Items]
Number of assets to be sold (in properties) | property			4	1	5					4
Gain (loss) on sales of real estate, net												$ 41,000,000
Other non-reportable segments
Real Estate [Line Items]
Number of assets to be sold (in properties) | property			2							2
SHOP
Real Estate [Line Items]
Proceeds from sale of buildings			$ 92,000,000	$ 7,000,000	$ 14,000,000	$ 68,000,000
Life science
Real Estate [Line Items]
Proceeds from sale of buildings					7,000,000	35,000,000
Senior housing triple-net
Real Estate [Line Items]
Proceeds from sale of buildings						$ 26,000,000
Medical office
Real Estate [Line Items]
Proceeds from sale of buildings			5,000,000	$ 3,000,000	$ 15,000,000
Other non-reportable segments
Real Estate [Line Items]
Proceeds from sale of buildings			$ 20,000,000