Credit Concentration (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($) properties	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) properties	Jun. 30, 2017 USD ($)	Dec. 31, 2017
Concentration by investment:
Number of properties in diversified portfolio | properties	1,257		1,257
Net Operating Income	$ 557,161	$ 556,747	$ 1,097,661	$ 1,108,876
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			$ 1,097,661
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			$ 165,935
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			8.00%
Net Operating Income			$ 83,467
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			$ 78,233
Genesis HealthCare [Member]
Concentration by investment:
Number of properties in diversified portfolio | properties	86		86
Genesis HealthCare [Member] | Net Operating Income [Member]
Concentration by investment:
Percent of NOI			6.00%
Net Operating Income			$ 67,546
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			5.00%
Net Operating Income			$ 49,941
Remaining Portfolio [Member]
Concentration by investment:
Number of properties in diversified portfolio | properties	727		727
Remaining Portfolio [Member] | Net Operating Income [Member]
Concentration by investment:
Percent of NOI			59.00%
Net Operating Income			$ 652,539