Credit Concentration (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) properties	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) properties	Sep. 30, 2017 USD ($)	Dec. 31, 2017
Concentration by investment:
Number of properties in diversified portfolio | properties	1,529		1,529
Net Operating Income	$ 579,222	$ 567,486	$ 1,676,883	$ 1,676,362
Credit Concentration (Textual) [Abstract]
Percentage total investments with top five customers					41.00%
Net Operating Income [Member]
Concentration by investment:
Percent of NOI			100.00%
Net Operating Income			$ 1,676,883
Sunrise Senior Living Inc. [Member]
Concentration by investment:
Number of properties in diversified portfolio | properties	161		161
Sunrise Senior Living Inc. [Member] | Net Operating Income [Member]
Concentration by investment:
Percent of NOI			15.00%
Net Operating Income			$ 252,111
Brookdale [Member]
Concentration by investment:
Number of properties in diversified portfolio | properties	137		137
Brookdale [Member] | Net Operating Income [Member]
Concentration by investment:
Percent of NOI			7.00%
Net Operating Income			$ 117,367
Revera [Member]
Concentration by investment:
Number of properties in diversified portfolio | properties	98		98
Revera [Member] | Net Operating Income [Member]
Concentration by investment:
Percent of NOI			7.00%
Net Operating Income			$ 116,158
Genesis HealthCare [Member]
Concentration by investment:
Number of properties in diversified portfolio | properties	88		88
Genesis HealthCare [Member] | Net Operating Income [Member]
Concentration by investment:
Percent of NOI			6.00%
Net Operating Income			$ 102,015
Benchmark Senior Living [Member]
Concentration by investment:
Number of properties in diversified portfolio | properties	48		48
Benchmark Senior Living [Member] | Net Operating Income [Member]
Concentration by investment:
Percent of NOI			4.00%
Net Operating Income			$ 75,435
Remaining Portfolio [Member]
Concentration by investment:
Number of properties in diversified portfolio | properties	997		997
Remaining Portfolio [Member] | Net Operating Income [Member]
Concentration by investment:
Percent of NOI			61.00%
Net Operating Income			$ 1,013,797