Recent Transactions (Schedule Of Dispositions/Rental Property Held For Sale) (Details)
$ in Thousands
 6 Months Ended 12 Months Ended
Jun. 30, 2016
USD ($)
ft²
item
Dec. 31, 2015
USD ($)
Dec. 31, 2012
USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]      
Number of Buildings, Disposed | item 5    
Rentable Square Feet, Disposed | ft² 959,116    
Net Sales Proceeds $ 359,515    
Net Book Value 270,183    
Realized Gain (loss)/Unrealized Loss 89,332    
Mortgage loans, carrying amount 1,694,252    
Unrealized losses on properties held for sale (3,615)    
Totals $ 85,717    
2 Independence Way [Member]      
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]      
Number of Buildings, Disposed | item [1] 1    
Rentable Square Feet, Disposed | ft² [1] 67,401    
Net Sales Proceeds [1] $ 4,119    
Net Book Value [1] 4,283    
Realized Gain (loss)/Unrealized Loss [1] $ (164)    
Impairments   $ 3,200  
1201 Connecticut Avenue NW [Member]      
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]      
Number of Buildings, Disposed | item 1    
Rentable Square Feet, Disposed | ft² 169,549    
Net Sales Proceeds $ 90,591    
Net Book Value 31,827    
Realized Gain (loss)/Unrealized Loss $ 58,764    
125 Broad Street [Member]      
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]      
Number of Buildings, Disposed | item [2] 1    
Rentable Square Feet, Disposed | ft² [2] 524,476    
Net Sales Proceeds [2] $ 192,323    
Net Book Value [2] 200,183    
Realized Gain (loss)/Unrealized Loss [2] $ (7,860)    
Impairments   $ 83,200  
9200 Edmonston Road [Member]      
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]      
Number of Buildings, Disposed | item 1    
Rentable Square Feet, Disposed | ft² 38,690    
Net Sales Proceeds [3] $ 4,083    
Net Book Value 3,837    
Realized Gain (loss)/Unrealized Loss $ 246    
Impairments     $ 3,000
1400 L Street, NW [Member]      
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]      
Number of Buildings, Disposed | item 1    
Rentable Square Feet, Disposed | ft² 159,000    
Net Sales Proceeds [4] $ 68,399    
Net Book Value 30,053    
Realized Gain (loss)/Unrealized Loss 38,346    
Net sales proceeds held by qualified intermediary $ 28,500    
[1] The Company recorded an impairment charge of $3.2 million on this property during the year ended December 31, 2015 as it estimated that the carrying value of the property may not be recoverable over its anticipated holding period.
[2] The disposition represented two units of office condominium interests which collectively comprised floors 2 through 16 of the 40-story building. The Company recorded impairment charges of $83.2 million on this property during the year ended December 31, 2015 as it estimated that the carrying value of the property may not be recoverable over its anticipated holding period.
[3] The Company transferred the deed for this property to the lender in satisfaction of its obligations. The Company recorded an impairment charge of $3.0 million on this property during the year ended December 31, 2012 as it estimated that the carrying value of the property may not be recoverable over its anticipated holding period.
[4] $28.5 million of the net sales proceeds are held by a qualified intermediary until such funds are used in acquisitions.