Annual report pursuant to Section 13 and 15(d)

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

v3.10.0.1
Disclosure Of Fair Value Of Assets And Liabilities (Narrative) (Details)
 12 Months Ended
Dec. 31, 2018
USD ($)
property
item
Dec. 31, 2017
USD ($)
property
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value of Company's long-term debt $ 2,711,712,000 $ 2,764,033,000
Principal balance outstanding 2,792,651,000 2,809,568,000
Aggregate carrying value 108,848,000 171,578,000
Land impairments 24,566,000  
Office [Member] | Fort Lee, Newark, Paramus, Bridgewater, Morris Plains And Rahway, New Jersey [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Unrealized losses on rental properties held for sale 20,100,000  
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Parsippany, Paramus, Rochelle Park, Hamilton And Wall, New Jersey And White Plains, New York [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Aggregate carrying value   $ 171,578,000
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Fort Lee, Newark, Paramus, Bridgewater, Morris Plains And Rahway, New Jersey [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Aggregate carrying value $ 108,848,000  
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Office [Member] | Parsippany, Paramus, Rochelle Park, Hamilton And Wall, New Jersey And White Plains, New York [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Number of properties held for sale | property   21
Aggregate carrying value   $ 171,600,000
Estimated expected sales proceeds   $ 223,000,000
Number of properties not expected to recover from estimated net sales proceeds | property   7
Unrealized losses on rental properties held for sale   $ 12,300,000
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Office [Member] | Fort Lee, Newark, Paramus, Bridgewater, Morris Plains And Rahway, New Jersey [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Number of properties held for sale | property 6  
Aggregate carrying value $ 108,800,000  
Estimated expected sales proceeds $ 124,000,000  
Number of properties not expected to recover from estimated net sales proceeds | property 4  
Unrealized losses on rental properties held for sale $ 20,100,000  
Number of real estate properties | item 159  
Disposal Group, Not Discontinued Operations [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Unrealized losses on rental properties held for sale $ (20,135,000) $ (12,331,000)