Credit Concentration (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018 USD ($) properties	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) properties	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Concentration by investment:
Number of properties | properties	1,510								1,510
Total NOI									$ 2,267,482	$ 2,232,716	$ 2,404,177
Credit Concentration (Textual) [Abstract]
Percentage total investments with top five customers					41.00%					41.00%
Revenues	$ 1,241,243	$ 1,236,379	$ 1,125,912	$ 1,096,965	$ 1,104,257	$ 1,091,483	$ 1,058,602	$ 1,062,298	$ 4,700,499	$ 4,316,641	$ 4,281,160
Sunrise Senior Living(
Concentration by investment:
Number of properties | properties	161								161
Credit Concentration (Textual) [Abstract]
Revenues									$ 1,154,025
Revera
Concentration by investment:
Number of properties | properties	98								98
Brookdale Senior Living
Concentration by investment:
Number of properties | properties	102								102
Genesis HealthCare
Concentration by investment:
Number of properties | properties	87								87
Benchmark Senior Living
Concentration by investment:
Number of properties | properties	48								48
Remaining portfolio
Concentration by investment:
Number of properties | properties	1,014								1,014
Net Operating Income [Member]
Concentration by investment:
Total NOI									$ 2,267,482
Percent of NOI									100.00%
Net Operating Income [Member] | Sunrise Senior Living(
Concentration by investment:
Total NOI									$ 335,456
Percent of NOI									15.00%
Net Operating Income [Member] | Revera
Concentration by investment:
Total NOI									$ 154,194
Percent of NOI									7.00%
Net Operating Income [Member] | Brookdale Senior Living
Concentration by investment:
Total NOI									$ 142,768
Percent of NOI									6.00%
Net Operating Income [Member] | Genesis HealthCare
Concentration by investment:
Total NOI									$ 137,054
Percent of NOI									6.00%
Net Operating Income [Member] | Benchmark Senior Living
Concentration by investment:
Total NOI									$ 99,439
Percent of NOI									4.00%
Net Operating Income [Member] | Remaining portfolio
Concentration by investment:
Total NOI									$ 1,398,571
Percent of NOI									62.00%