Credit Concentration (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($) property	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) property	Jun. 30, 2018 USD ($)	Dec. 31, 2018
Concentration Risk [Line Items]
Total NOI	$ 618,979	$ 557,161	$ 1,220,417	$ 1,097,661
Percentage total investments with top five customers					38.00%
Net Operating Income
Concentration Risk [Line Items]
Number of Properties | property	1,598		1,598
Total NOI			$ 1,220,417
Percent of NOI			100.00%
Net Operating Income | Sunrise Senior Living
Concentration Risk [Line Items]
Number of Properties | property	165		165
Total NOI			$ 174,422
Percent of NOI			14.00%
Net Operating Income | ProMedica
Concentration Risk [Line Items]
Number of Properties | property	218		218
Total NOI			$ 107,541
Percent of NOI			9.00%
Net Operating Income | Revera
Concentration Risk [Line Items]
Number of Properties | property	98		98
Total NOI			$ 72,928
Percent of NOI			6.00%
Net Operating Income | Genesis HealthCare
Concentration Risk [Line Items]
Number of Properties | property	60		60
Total NOI			$ 60,984
Percent of NOI			5.00%
Net Operating Income | Benchmark Senior Living
Concentration Risk [Line Items]
Number of Properties | property	48		48
Total NOI			$ 55,530
Percent of NOI			5.00%
Net Operating Income | Remaining portfolio
Concentration Risk [Line Items]
Number of Properties | property	1,009		1,009
Total NOI			$ 749,012
Percent of NOI			61.00%