Quarterly report pursuant to Section 13 or 15(d)

Disclosure Of Fair Value Of Assets And Liabilities (Narrative) (Details)

v3.19.3
Disclosure Of Fair Value Of Assets And Liabilities (Narrative) (Details)
 3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2019
USD ($)
Jun. 30, 2019
USD ($)
ft²
Sep. 30, 2019
USD ($)
property
Dec. 31, 2018
USD ($)
property
Sep. 30, 2019
item
Sep. 30, 2019
ft²
Sep. 30, 2019
property
Fair Value Measurement Inputs and Valuation Techniques [Line Items]              
Fair value of Company's long-term debt $ 3,127,626,000   $ 3,127,626,000 $ 2,711,712,000      
Principal balance outstanding 3,151,561,000   3,151,561,000 $ 2,792,651,000      
Land and other Impairments 6,345,000   8,844,000        
Property impairments 5,894,000   11,696,000        
Properties aggregate net book value     419,200,000        
Conshohocken And Bala Cynwyd, Pennsylvania [Member]              
Fair Value Measurement Inputs and Valuation Techniques [Line Items]              
Number of real estate properties | property       2     2
Land and other Impairments 200,000   2,700,000        
Property And Undeveloped Land [Member]              
Fair Value Measurement Inputs and Valuation Techniques [Line Items]              
Land impairments     451,000        
Land and other Impairments     6,100,000        
Property impairments     5,900,000        
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Conshohocken And Bala Cynwyd, Pennsylvania [Member]              
Fair Value Measurement Inputs and Valuation Techniques [Line Items]              
Land and other Impairments       $ 24,600,000      
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Fort Lee, Parsippany, Hanover And Neptune, New Jersey, And Malden And Revere, Massachusetts [Member]              
Fair Value Measurement Inputs and Valuation Techniques [Line Items]              
Estimated expected sales proceeds     $ 536,600,000        
Number of properties not expected to recover from estimated net sales proceeds | property     2        
Unrealized losses on rental properties held for sale $ 35,100,000            
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Office [Member] | Fort Lee, Parsippany, Hanover And Neptune, New Jersey, And Malden And Revere, Massachusetts [Member]              
Fair Value Measurement Inputs and Valuation Techniques [Line Items]              
Number of properties held for sale | property             3
Area of property (in square feet) | ft²           697,000  
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Multi-Family Properties [Member] | Fort Lee, Parsippany, Hanover And Neptune, New Jersey, And Malden And Revere, Massachusetts [Member]              
Fair Value Measurement Inputs and Valuation Techniques [Line Items]              
Number of properties held for sale         1,386   3
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Retail Property [Member] | Fort Lee, Parsippany, Hanover And Neptune, New Jersey, And Malden And Revere, Massachusetts [Member]              
Fair Value Measurement Inputs and Valuation Techniques [Line Items]              
Number of properties held for sale | property             1
Disposal Group, Not Discontinued Operations [Member]              
Fair Value Measurement Inputs and Valuation Techniques [Line Items]              
Unrealized losses on rental properties held for sale     $ (35,079,000)        
Parsippany [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member]              
Fair Value Measurement Inputs and Valuation Techniques [Line Items]              
Area of property (in square feet) | ft²   317,040       317,040  
Valuation impairment charge   $ 5,800,000