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 | |
Boston-Downtown Crossing [Member] | |||
| Percentage of interest in venture | 15.00% | ||
| Area of office property | 1,200,000 | ||
| Venture property acquisition cost | $ 100 | ||
| Impairment of real estate | $ 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. | ||