Investments In Unconsolidated Joint Ventures (Boston-Downtown Crossing) (Narrative) (Details) (USD $)
 12 Months Ended 0 Months Ended 12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Apr. 23, 2013
Boston-Downtown Crossing [Member]
Dec. 31, 2013
Boston-Downtown Crossing [Member]
sqft
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 $ 83,371,000 [1] $ 87,000 [2]   $ 754,000
[1] This amount, net of impairment charges recorded in 2013 of $23,851,000 on certain of the properties prior to their sale (per Note [d] above), comprises the $59,520,000 of realized gains (losses) and unrealized losses on disposition of rental property and impairments, net, for the year ended December 31, 2013.  See Note 7: Discontinued Operations.
[2] Also included in realized gains(loss) for the year ended December 31, 2012, was a $4.5 million gain recorded on the disposal of the office property located at 2200 Renaissance Boulevard. This office property, aggregating 174,124 square feet, was collateral for a $16.2 million mortgage loan scheduled to mature on December 1, 2012. The Company previously recorded an impairment charge on the property of $9.5 million at December 31, 2010. On March 28, 2012, the Company transferred the deed for 2200 Renaissance Boulevard to the lender in satisfaction of its obligations, which resulted in recording the gain.