Quarterly report pursuant to Section 13 or 15(d)

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

v3.8.0.1
Disclosure Of Fair Value Of Assets And Liabilities (Narrative) (Details)
 3 Months Ended 12 Months Ended
Mar. 31, 2018
USD ($)
property
Dec. 31, 2017
USD ($)
property
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Fair value of Company's long-term debt $ 2,534,001,000 $ 2,764,033,000
Principal balance outstanding 2,615,211,000 2,809,568,000
Aggregate carrying value 38,566,000 $ 171,578,000
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Paramus And Rochelle Park [Member]    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Aggregate carrying value $ 38,566,000  
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 Inputs, Assets, Quantitative Information [Line Items]    
Number of properties held for sale | property   21
Aggregate carrying value   $ 171,600,000
Unrealized losses on rental properties held for sale   $ 12,300,000
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Office [Member] | Paramus, Rochelle Park, Hamilton And Wall, New Jersey And White Plains, New York [Member]    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Number of properties not expected to recover from estimated net sales proceeds | property   7
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Office [Member] | Paramus And Rochelle Park [Member]    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Number of properties held for sale | property 2  
Estimated expected sales proceeds $ 41,400,000  
Disposal Group, Not Discontinued Operations [Member]    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Sales proceeds $ 223,049,000