Credit Concentration (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019 USD ($) property	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) property	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Concentration Risk [Line Items]
Total NOI									$ 2,431,264	$ 2,267,482	$ 2,232,716
Percentage total investments with top five customers					38.00%					38.00%
Revenues	$ 1,262,822	$ 1,266,133	$ 1,320,106	$ 1,272,245	$ 1,241,243	$ 1,236,379	$ 1,125,912	$ 1,096,965	5,121,306	$ 4,700,499	$ 4,316,641
Sunrise Senior Living
Concentration Risk [Line Items]
Revenues									$ 1,219,253
Net Operating Income
Concentration Risk [Line Items]
Number of properties | property	1,578								1,578
Total NOI									$ 2,431,264
Percent of NOI									100.00%
Net Operating Income | Sunrise Senior Living
Concentration Risk [Line Items]
Number of properties | property	165								165
Total NOI									$ 342,595
Percent of NOI									14.00%
Net Operating Income | ProMedica
Concentration Risk [Line Items]
Number of properties | property	218								218
Total NOI									$ 215,083
Percent of NOI									9.00%
Net Operating Income | Revera
Concentration Risk [Line Items]
Number of properties | property	94								94
Total NOI									$ 146,451
Percent of NOI									6.00%
Net Operating Income | Genesis HealthCare
Concentration Risk [Line Items]
Number of properties | property	54								54
Total NOI									$ 119,928
Percent of NOI									5.00%
Net Operating Income | Belmont Village
Concentration Risk [Line Items]
Number of properties | property	21								21
Total NOI									$ 76,354
Percent of NOI									3.00%
Net Operating Income | Remaining portfolio
Concentration Risk [Line Items]
Number of properties | property	1,026								1,026
Total NOI									$ 1,530,853
Percent of NOI									63.00%