Quarterly report pursuant to Section 13 or 15(d)

Discontinued Operations (Narrative) (Details)

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Discontinued Operations (Narrative) (Details) (USD $)
 0 Months Ended 3 Months Ended 12 Months Ended 3 Months Ended 3 Months Ended
Mar. 31, 2012
Dec. 31, 2011
Mar. 28, 2012
2200 Renaissance Boulevard [Member]
sqft
Mar. 31, 2012
2200 Renaissance Boulevard [Member]
Dec. 31, 2010
2200 Renaissance Boulevard [Member]
Mar. 31, 2012
Montvale, New Jersey [Member]
sqft
Mar. 31, 2012
Moorestown, New Jersey [Member]
sqft
Mar. 31, 2012
Montvale And Moorestown, New Jersey [Member]
Schedule of Equity Method Investments [Line Items]                
Aggregate square foot of the property     174,124     47,700 222,258  
Mortgage loan face amount     $ 16,200,000          
Mortgage loan, maturity date       December 1, 2012        
Impairment charge on property         9,500,000      
Gain recorded on disposal of office property     4,500,000          
Valuation allowance recognized           500,000   500,000
Aggregate book value of real estate properties 3,815,188,000 3,870,607,000           23,900,000
Net accumulated depreciation $ 1,377,152,000 $ 1,409,163,000           $ 10,000,000
Number of office buildings             3  
Number of properties held for sale               4