Segment Information (Geographic Information) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue
Revenues	$ 921,165	$ 918,940	$ 943,198	$ 1,012,054	$ 996,004	$ 983,155	$ 950,717	$ 942,874	$ 3,795,357	$ 3,872,750	$ 3,745,810
Net real estate property:
Net real estate property	20,550,035				21,734,573				20,550,035	21,734,573
United States
Revenue
Revenues									3,381,357	3,578,341	3,524,875
Net real estate property:
Net real estate property	17,303,816				18,636,838				17,303,816	18,636,838
Canada
Revenue
Revenues									389,205	266,946	192,350
Net real estate property:
Net real estate property	2,983,924				2,830,850				2,983,924	2,830,850
United Kingdom
Revenue
Revenues									24,795	27,463	$ 28,585
Net real estate property:
Net real estate property	$ 262,295				$ 266,885				$ 262,295	$ 266,885