Fair Value Disclosures (Fair Value Of Notes Receivable And Notes Payable) (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
Carrying Value	$ 2,589,900,000	$ 2,530,800,000
Balances outstanding under our unsecured notes line of credit and short-term borrowings	1,649,041,000	1,588,798,000
Fixed rate notes payable
Carrying Value	2,319,000,000	2,319,500,000
Estimated Fair Value	2,433,400,000	2,391,500,000
Floating rate notes payable (1)
Carrying Value	270,900,000	211,300,000	212,400,000
Estimated Fair Value	263,500,000	201,400,000
Line of Credit [Member] | Commercial Banks [Member]
Balances outstanding under our unsecured notes line of credit and short-term borrowings	$ 60,000,000	$ 0