Segment Information (Geographic Information) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue
Revenues	$ 996,004	$ 983,155	$ 950,717	$ 942,874	$ 923,263	$ 936,538	$ 942,304	$ 943,705	$ 3,872,750	$ 3,745,810	$ 3,574,149
Net real estate property:
Net real estate property	21,729,087				20,093,657				21,729,087	20,093,657
United States
Revenue
Revenues									3,578,341	3,524,875	3,361,682
Net real estate property:
Net real estate property	18,631,352				18,861,163				18,631,352	18,861,163
Canada
Revenue
Revenues									266,946	192,350	186,049
Net real estate property:
Net real estate property	2,830,850				963,588				2,830,850	963,588
United Kingdom
Revenue
Revenues									27,463	28,585	$ 26,418
Net real estate property:
Net real estate property	$ 266,885				$ 268,906				$ 266,885	$ 268,906