Activity for Real Estate Investments and Accumulated Depreciation (Details) - USD ($)		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Real Estate Investments [Abstract]
Balance at beginning of year		$ (12,972,170,000)	$ (8,215,768,000)	$ (8,069,395,000)
Acquisitions	[1]	127,710,000	4,961,140,000	316,151,000
Less: FMV of Leases included in Acquisitions		(1,488,000)	(51,588,000)	(4,438,000)
Improvement and development		322,829,000	202,614,000	165,000,000
Disposition of real estate assets	[2]	(123,861,000)	(355,764,000)	(330,340,000)
Balance at end of year		(13,292,039,000)	(12,972,170,000)	(8,215,768,000)
Real Estate and Accumulated Depreciation Disclosure [Abstract]
Balance at beginning of year		1,674,801,000	1,499,213,000	1,373,678,000
Depreciation		463,590,000	314,076,000	289,177,000
Disposition of real estate assets	[2]	(63,320,000)	(138,488,000)	(163,642,000)
Balance at end of year		2,075,071,000	1,674,801,000	1,499,213,000
Assets Held-for-sale
Real Estate Investments [Abstract]
Balance at beginning of year		0	0
Balance at end of year		(5,321,000)	0	0
Real Estate and Accumulated Depreciation Disclosure [Abstract]
Accumulated depreciation		$ 0	$ 0	$ 0

[1] Includes non-cash activity related to acquisitions.

[2] Includes assets sold, casualty losses, and removal of certain fully depreciated assets.