Acquisitions and Dispositions (Narrative) (Details) (USD $)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2014 acre entities	Jun. 30, 2013	Jun. 30, 2014 buildings acre entities	Jun. 30, 2013	Dec. 31, 2013 buildings
Operating Leases, Income Statement, Lease Revenue	$ 233,518,000	$ 215,308,000	$ 470,868,000	$ 425,187,000
Operating Income (Loss)	189,788,000	44,568,000	256,310,000	136,751,000
Business Combination, Acquisition Related Costs			761,000	2,700,000
Gain Loss On Business Combinations Excluding Acquisitions Costs				(962,000)
Number of Real Estate Properties Sold			21		38
Area of Land	86		86
Proceeds from land and depreciated property sales, net			213,040,000	259,169,000
Income Tax Expense (Benefit)	364,000	0	3,038,000	0
Discontinued Operation, Tax Effect of Discontinued Operation	546,000	0	3,523,000	0
Number of Unconsolidated Joint Ventures in which Equity Interests Held	2		2
Capital distributions from unconsolidated companies			40,293,000	89,237,000
Earnings from Depreciated Property Sales Share of Joint Venture			58,300,000
Other Two Thousand Fourteen Acquisitions [Member] [Domain] [Member] [Member]
Weighted average remaining life of property (years)			9 years 1 month 26 days
Operating Leases, Income Statement, Lease Revenue			1,600,000
Operating Income (Loss)			$ 5,000
Industrial [Member] | Other Two Thousand Fourteen Acquisitions [Member] [Domain] [Member] [Member]
Number of real estate properties acquired	2		2
Office [Member] | Unconsolidated Properties [Member]
Number of Real Estate Properties Sold			2
Square Footage Of Real Estate Properties Acquired Or Disposed			436,000