Credit Concentration (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($) property	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) property	Sep. 30, 2018 USD ($)	Dec. 31, 2018
Concentration Risk [Line Items]
Total NOI	$ 610,545	$ 579,222	$ 1,830,962	$ 1,676,883
Percentage total investments with top five customers					38.00%
Net Operating Income
Concentration Risk [Line Items]
Number of Properties | property	1,539		1,539
Total NOI			$ 1,830,962
Percent of NOI			100.00%
Net Operating Income | Sunrise Senior Living
Concentration Risk [Line Items]
Number of Properties | property	165		165
Total NOI			$ 257,372
Percent of NOI			14.00%
Net Operating Income | ProMedica
Concentration Risk [Line Items]
Number of Properties | property	218		218
Total NOI			$ 161,313
Percent of NOI			9.00%
Net Operating Income | Revera
Concentration Risk [Line Items]
Number of Properties | property	98		98
Total NOI			$ 109,953
Percent of NOI			6.00%
Net Operating Income | Genesis HealthCare
Concentration Risk [Line Items]
Number of Properties | property	54		54
Total NOI			$ 90,451
Percent of NOI			5.00%
Net Operating Income | Belmont Village
Concentration Risk [Line Items]
Number of Properties | property	21		21
Total NOI			$ 59,763
Percent of NOI			3.00%
Net Operating Income | Remaining portfolio
Concentration Risk [Line Items]
Number of Properties | property	983		983
Total NOI			$ 1,152,110
Percent of NOI			63.00%