Quarterly report pursuant to Section 13 or 15(d)

Investments In Unconsolidated Joint Ventures (Boston-Downtown Crossing) (Details)

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Investments In Unconsolidated Joint Ventures (Boston-Downtown Crossing) (Details) (Boston-Downtown Crossing [Member], USD $)
In Millions, unless otherwise specified
1 Months Ended 12 Months Ended
Jan. 29, 2007
Oct. 31, 2006
sqft
Dec. 31, 2008
Schedule of Equity Method Investments [Line Items]      
Percentage of interest in venture   15.00%  
Area of office property, square feet   1,200,000  
Venture property acquisition cost $ 100    
Impairment of property     $ 69.5
Holding and distribution pattern under operating agreement  
Distributions will generally be in proportion to its members' respective ownership interests and, depending upon the development unit, promotes will be available to specified partners after the achievement of certain internal rates of return ranging from 10 to 15 percent.
 
Maximum [Member]
     
Schedule of Equity Method Investments [Line Items]      
Internal rate of return   15.00%  
Minimum [Member]
     
Schedule of Equity Method Investments [Line Items]      
Internal rate of return   10.00%