Segment Information (Geographic Information) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenue
Total revenues	$ 841,274	$ 827,606	$ 811,920	$ 805,598	$ 732,090	$ 704,932	$ 674,529	$ 665,262	$ 3,286,398	$ 2,776,813	$ 2,516,617
Net real estate property:
Net real estate property	19,625,220				16,772,990				19,625,220	16,772,990
United States
Revenue
Total revenues									3,086,449	2,636,591	2,423,399
Net real estate property:
Net real estate property	18,271,829				15,334,686				18,271,829	15,334,686
Canada
Revenue
Total revenues									173,778	126,435	93,218
Net real estate property:
Net real estate property	1,039,561				1,269,710				1,039,561	1,269,710
United Kingdom
Revenue
Total revenues									26,171	13,787	$ 0
Net real estate property:
Net real estate property	$ 313,830				$ 168,594				$ 313,830	$ 168,594