Fair Value Disclosures (Fair Value Of Notes Receivable And Notes Payable) (Details) (USD $)	9 Months Ended			3 Months Ended		1 Months Ended
	Sep. 30, 2011	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2011 Commercial Banks [Member] Term Loan, Due 2012 [Member]	Dec. 31, 2010 Term Loan [Member]	Jul. 31, 2011 Construction Loan [Member]	Sep. 30, 2011 Construction Loan [Member]	Dec. 31, 2010 Construction Loan [Member]	Sep. 30, 2011 Fixed Rate Notes Payable [Member]		Dec. 31, 2010 Fixed Rate Notes Payable [Member]		Sep. 30, 2011 Floating Rate Notes Payable [Member]	Dec. 31, 2010 Floating Rate Notes Payable [Member]
Notes receivable - affiliates, Carrying Value			$ 3,194,000
Notes receivable - affiliates, Estimated Fair Value			3,200,000
Carrying Value	2,433,100,000		2,563,800,000						2,187,200,000	[1]	2,333,500,000	[1]	245,900,000	230,300,000
Estimated Fair Value									2,276,400,000	[1]	2,386,000,000	[1]	234,300,000	212,700,000
Fixed rate notes payable					500,000,000		16,600,000	16,600,000
Aggregate face amount of debt offerings completed during the period		500,000,000
Construction loan extension date						July 2011
Repayment of senior unsecured notes	$ 500,000,000			$ 500,000,000

[1] December 31, 2010 includes a $500 million term loan entered into in 2007, and a $16.6 million construction loan entered into in 2008 which are effectively fixed by the use of interest rate swaps but evaluated for estimated fair value at the floating rate. The $500 million term loan was repaid in June 2011 from the net proceeds received from our $500 million debt offerings also completed in June 2011 and with cash on hand. The $16.6 million construction loan interest rate swap matured and was not extended in conjunction with the one-year extension of the loan in July 2011.