Acquisitions and Dispositions (Narrative) (Details) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2014 entities	Sep. 30, 2013	Sep. 30, 2014 buildings entities	Sep. 30, 2013	Dec. 31, 2013 buildings
Operating Leases, Income Statement, Lease Revenue	$ 231,322,000	$ 221,655,000	$ 702,190,000	$ 646,842,000
Operating Income (Loss)	123,073,000	44,097,000	379,686,000	180,847,000
Business Combination, Acquisition Related Costs			871,000	3,500,000
Gain Loss On Business Combinations Excluding Acquisitions Costs				(962,000)
Number of Real Estate Properties Sold			23		38
Proceeds from land and depreciated property sales, net			386,215,000	330,740,000
Income Tax Expense (Benefit)	(442,000)	(4,500,000)	2,595,000	(4,500,000)
Discontinued Operation, Tax Effect of Discontinued Operation	(555,000)	0	2,969,000	0
Number of Unconsolidated Joint Ventures in which Equity Interests Held	4		4
Capital distributions from unconsolidated companies			70,054,000	106,306,000
Earnings from Depreciated Property Sales Share of Joint Venture			75,500,000
Other Two Thousand Fourteen Acquisitions [Member] [Domain] [Member] [Member]
Weighted average remaining life of property (years)			8 years 8 months 13 days
Operating Leases, Income Statement, Lease Revenue			3,200,000
Operating Income (Loss)			$ 45,000
Industrial [Member] | Other Two Thousand Fourteen Acquisitions [Member] [Domain] [Member] [Member]
Number of real estate properties acquired	3		3
Acres Sold [Member]
Area of Land	159		159
Office [Member] | Unconsolidated Properties [Member]
Number of Real Estate Properties Sold			5
Industrial [Member] | Unconsolidated Properties [Member]
Number of Real Estate Properties Sold			11
Square Footage Of Real Estate Properties Acquired Or Disposed			2,072,000
Atlanta Georgia [Member] | Office [Member] | Unconsolidated Properties [Member]
Square Footage Of Real Estate Properties Acquired Or Disposed			436,000
Central Florida [Member] | Office [Member] | Unconsolidated Properties [Member]
Square Footage Of Real Estate Properties Acquired Or Disposed			415,000