Activity for Real Estate Investments and Accumulated Depreciation (Details) - USD ($)		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Real Estate Investments [Abstract]
Balance at beginning of year		$ 8,215,768,000	$ 8,069,395,000	$ 7,722,181,000
Acquisitions	[1]	4,961,140,000	316,151,000	407,889,000
Less: FMV of Leases included in Acquisitions		(51,588,000)	(4,438,000)	(4,968,000)
Improvement and development		202,614,000	165,000,000	186,043,000
Disposition of real estate assets	[2]	(355,764,000)	(330,340,000)	(241,750,000)
Balance at end of year		12,972,170,000	8,215,768,000	8,069,395,000
Real Estate and Accumulated Depreciation Disclosure [Abstract]
Balance at beginning of year		1,499,213,000	1,373,678,000	1,138,315,000
Depreciation		314,076,000	289,177,000	276,991,000
Disposition of real estate assets	[2]	(138,488,000)	(163,642,000)	(41,628,000)
Balance at end of year		1,674,801,000	1,499,213,000	1,373,678,000
Commercial
Real Estate and Accumulated Depreciation Disclosure [Abstract]
Accumulated depreciation		18,730,000	16,845,000	15,279,000
Assets Held-for-sale
Real Estate Investments [Abstract]
Balance at beginning of year		0	0
Balance at end of year		0	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.