Segment Information (Geographic Information) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue
Total revenues	$ 875,713	$ 867,116	$ 848,404	$ 852,289	$ 841,274	$ 827,606	$ 811,920	$ 805,598	$ 3,443,522	$ 3,286,398	$ 2,776,813
Net real estate property:
Net real estate property	20,394,754				19,625,220				20,394,754	19,625,220
United States
Revenue
Total revenues									3,242,353	3,086,449	2,636,591
Net real estate property:
Net real estate property	19,105,939				18,271,829				19,105,939	18,271,829
Canada
Revenue
Total revenues									174,831	173,778	126,435
Net real estate property:
Net real estate property	1,037,105				1,039,561				1,037,105	1,039,561
United Kingdom
Revenue
Total revenues									26,338	26,171	$ 13,787
Net real estate property:
Net real estate property	$ 251,710				$ 313,830				$ 251,710	$ 313,830