Credit Concentration (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) property	Mar. 31, 2018 USD ($)	Dec. 31, 2018
Concentration Risk [Line Items]
Total NOI	$ 601,438	$ 540,500
Percentage total investments with top five customers			38.00%
Net Operating Income
Concentration Risk [Line Items]
Number of Properties | property	1,494
Total NOI	$ 601,438
Percent of NOI	100.00%
Net Operating Income | Sunrise Senior Living Inc
Concentration Risk [Line Items]
Number of Properties | property	161
Total NOI	$ 90,592
Percent of NOI	15.00%
Net Operating Income | ProMedica
Concentration Risk [Line Items]
Number of Properties | property	218
Total NOI	$ 53,771
Percent of NOI	9.00%
Net Operating Income | Revera
Concentration Risk [Line Items]
Number of Properties | property	98
Total NOI	$ 36,682
Percent of NOI	6.00%
Net Operating Income | Genesis HealthCare
Concentration Risk [Line Items]
Number of Properties | property	63
Total NOI	$ 32,298
Percent of NOI	5.00%
Net Operating Income | Benchmark Senior Living
Concentration Risk [Line Items]
Number of Properties | property	48
Total NOI	$ 25,027
Percent of NOI	4.00%
Net Operating Income | Remaining portfolio
Concentration Risk [Line Items]
Number of Properties | property	906
Total NOI	$ 363,068
Percent of NOI	61.00%