Quarterly report pursuant to Section 13 or 15(d)

Recent Transactions (Schedule Of Disposed Properties) (Details)

v3.19.1
Recent Transactions (Schedule Of Disposed Properties) (Details)
$ in Thousands
 3 Months Ended
Apr. 01, 2019
USD ($)
item
Mar. 31, 2019
USD ($)
ft²
item
shares
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]        
Valuation allowance   $ 11,600   $ 5,300
Disposal Group, Not Discontinued Operations [Member]        
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]        
Number of Buildings, Disposed | item   62    
Rentable Square Feet, Disposed | ft²   3,645,028    
Net Sales Proceeds   $ 555,635    
Net Carrying Value   285,026    
Realized Gains (losses)/Unrealized Losses, net   270,609    
Unrealized losses on rental properties held for sale   (2,500)    
Totals   $ 268,109    
Disposal Group, Not Discontinued Operations [Member] | 721 Route 202/206 South [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   192,741    
Net Sales Proceeds   $ 5,651    
Net Carrying Value   5,410    
Realized Gains (losses)/Unrealized Losses, net   $ 241    
Valuation allowance     $ 9,300  
Disposal Group, Not Discontinued Operations [Member] | Park Square [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    
Net Sales Proceeds   $ 34,045    
Net Carrying Value   34,032    
Realized Gains (losses)/Unrealized Losses, net   13    
Net sales proceeds held by qualified intermediary   $ 9,000    
Valuation allowance     6,300  
Disposal Group, Not Discontinued Operations [Member] | 2115 Linwood Avenue [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   68,000    
Net Sales Proceeds   $ 15,197    
Net Carrying Value   7,433    
Realized Gains (losses)/Unrealized Losses, net   $ 7,764    
Disposal Group, Not Discontinued Operations [Member] | 201 Littleton 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   88,369    
Net Sales Proceeds   $ 4,842    
Net Carrying Value   4,937    
Realized Gains (losses)/Unrealized Losses, net   (95)    
Net sales proceeds held by qualified intermediary   $ 4,900    
Valuation allowance     $ 3,600  
Disposal Group, Not Discontinued Operations [Member] | 320 & 321 University Avenue [Member]        
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]        
Number of Buildings, Disposed | item   2    
Rentable Square Feet, Disposed | ft²   147,406    
Net Sales Proceeds   $ 25,552    
Net Carrying Value   18,456    
Realized Gains (losses)/Unrealized Losses, net   $ 7,096    
Disposal Group, Not Discontinued Operations [Member] | Flex Portfolio [Member]        
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]        
Number of Buildings, Disposed | item   56    
Number of properties disposed | item   2    
Rentable Square Feet, Disposed | ft²   3,148,512    
Net Sales Proceeds   $ 470,348    
Net Carrying Value   214,758    
Realized Gains (losses)/Unrealized Losses, net   255,590    
Carrying Amount of Mortgages   350,000    
Net sales proceeds held by qualified intermediary   $ 251,000    
Redemption of common units, shares | shares   301,638    
Proceeds from sale of properties   $ 6,600    
Disposal Group, Not Discontinued Operations [Member] | Flex Portfolio [Member] | Unsecured Term Loan [Member]        
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]        
Repayment of mortgage loans   90,000    
Disposal Group, Not Discontinued Operations [Member] | Unsecured Revolving Credit Facility [Member] | Flex Portfolio [Member]        
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]        
Carrying Amount of Mortgages   $ 119,900    
Subsequent Event [Member] | Jersey City, New Jersey [Member]        
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]        
Number Of Units | item 377      
Funds from qualified intermediary $ 217,400