Quarterly report pursuant to Section 13 or 15(d)

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

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Investments In Unconsolidated Joint Ventures (Boston-Downtown Crossing) (Narrative) (Details) (USD $)
0 Months Ended 6 Months Ended
Apr. 23, 2013
Jun. 30, 2013
sqft
Schedule of Equity Method Investments [Line Items]    
Gain on sale of property   $ 37,609,000
Boston Downtown Crossing [Member]
   
Schedule of Equity Method Investments [Line Items]    
Area of property (in square feet)   1,200,000
Percentage of interest in venture   15.00%
Venture sale of real estate 45,000,000  
Share of gain on sale of real estate 13,500,000  
Gain on sale of property   $ 754,000
Minimum [Member]
   
Schedule of Equity Method Investments [Line Items]    
Percentage of interest in venture   7.50%
Maximum [Member]
   
Schedule of Equity Method Investments [Line Items]    
Percentage of interest in venture   80.00%