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Fair Value Disclosures (Estimated Fair Value of Notes Payable) (Details) (USD $)
9 Months Ended
Sep. 30, 2011
Dec. 31, 2010
Estimated fair values of notes payable [Abstract]  
Notes payable$ 2,548,822,000$ 2,616,986,000
Debt2,524,956,0002,656,560,000
Notes Payable Fair Values Hypothetical Percent Increase In Interest Rates1.00% 
Impact Of Overall One Percent Increase In Interest Rates Decrease In Fair Values Of Notes Payable$ 68,600,000 
Impact Of Overall One Percent Increase In Interest Rates Decrease In Fair Values Of Notes Payable Percent2.70%