Activity for Real Estate Investments and Accumulated Depreciation (Details) (USD $)	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Real Estate Investments [Abstract]
Balance at beginning of year	$ 3,729,706,000		$ 3,379,929,000		$ 2,941,261,000
Acquisitions	3,999,895,000	[1]	344,869,000	[1]	362,745,000	[1]
Less: FMV of Leases included in Acquisitions	(51,728,000)		(3,144,000)				(3,829,000)
Improvement and development	130,824,000		134,118,000		104,705,000
Disposition of real estate assets	(114,681,000)	[2]	(126,066,000)	[2]	(24,953,000)	[2]
Balance at end of year	7,689,119,000		3,729,706,000		3,379,929,000
Real Estate and Accumulated Depreciation Disclosure [Abstract]
Balance at beginning of year	1,040,473,000		973,126,000		873,903,000
Depreciation	165,885,000		124,691,000		112,726,000
Disposition of real estate assets	(61,879,000)	[2]	(57,344,000)	[2]	(13,503,000)	[2]
Balance at end of year	1,138,315,000		1,040,473,000		973,126,000
Commercial
Real Estate and Accumulated Depreciation Disclosure [Abstract]
Accumulated depreciation	14,108,000		12,855,000				11,402,000
Assets Held-for-sale
Real Estate Investments [Abstract]
Balance at beginning of year							0
Balance at end of year	(4,897,000)		0				0
Real Estate and Accumulated Depreciation Disclosure [Abstract]
Accumulated depreciation	$ (6,164,000)		$ 0		$ 0

[1] Includes non-cash activity related to the Colonial merger.

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