Annual report pursuant to Section 13 and 15(d)

Recent Transactions (Real Estate Held For Sale/Discontinued Operations/Dispositions) (Narrative) (Details)

v3.20.4
Recent Transactions (Real Estate Held For Sale/Discontinued Operations/Dispositions) (Narrative) (Details)
$ in Thousands
 1 Months Ended 12 Months Ended 14 Months Ended
Jan. 31, 2021
USD ($)
ft²
property
Dec. 31, 2020
USD ($)
ft²
item
property
Dec. 31, 2019
USD ($)
ft²
property
item
Dec. 31, 2018
USD ($)
Dec. 31, 2020
USD ($)
ft²
property
item
Dec. 19, 2019
ft²
Real Estate Properties [Line Items]            
Area Of Real Estate Property Sold | ft²     4,490,578      
Land and other impairments   $ 16,817 $ 32,444 $ 24,566    
Proceeds from the sale of property   64,947 825,613 $ 338,015    
Accumulated depreciation   656,331 558,617   $ 656,331  
Book value   $ 4,638,643 $ 4,256,681   $ 4,638,643  
Suburban Office Portfolio [Member]            
Real Estate Properties [Line Items]            
Area of property (in square feet) | ft²           6,600,000
Number of properties sold | property     2      
Area Of Real Estate Property Sold | ft²     497,000      
Gain (loss) on sale of property     $ 52,200      
Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] | Suburban Office Portfolio [Member]            
Real Estate Properties [Line Items]            
Area of property (in square feet) | ft²   3,200,000     3,200,000  
Number of properties sold | property         20  
Gain (loss) on sale of property         $ 377,400  
Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] | Properties Disposed Three [Member] | Subsequent Event [Member] | Suburban Office Portfolio [Member]            
Real Estate Properties [Line Items]            
Number of real estate properties | property 1          
Area of property (in square feet) | ft² 149,600          
Gain (loss) on sale of property $ 38,000          
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Suburban Office Portfolio [Member]            
Real Estate Properties [Line Items]            
Area of property (in square feet) | ft²     6,100,000      
Number of properties held for sale | property     35      
Number of disposal groups | item     12      
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Properties Disposed One [Member] | Suburban Office Portfolio [Member]            
Real Estate Properties [Line Items]            
Number of real estate properties | property   16     16  
Area of property (in square feet) | ft²   3,000,000.0     3,000,000.0  
Number of disposal groups | property   6        
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Properties Disposed Two [Member] | Suburban Office Portfolio [Member]            
Real Estate Properties [Line Items]            
Gain (loss) on sale of property   $ 652,400        
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Properties Disposed Four [Member] | Suburban Office Portfolio [Member]            
Real Estate Properties [Line Items]            
Number of properties held for sale | property   4     4  
Disposal Group, Not Discontinued Operations [Member]            
Real Estate Properties [Line Items]            
Unrealized losses on rental properties held for sale   $ (1,682) $ (39,049)      
Gain (loss) on sale of property   $ 7,163 382,151      
Disposal Group, Not Discontinued Operations [Member] | Properties Disposed Two [Member] | Suburban Office Portfolio [Member]            
Real Estate Properties [Line Items]            
Number of real estate properties | property   15     15  
Area of property (in square feet) | ft²   2,800,000     2,800,000  
Discontinued Operations [Member]            
Real Estate Properties [Line Items]            
Unrealized losses on rental properties held for sale   $ (14,040) (135,052)      
Gain (loss) on sale of property   25,241 $ 1,702      
Parsippany, Madison, Short Hills, Edison, And Red Bank, New Jersey [Member]            
Real Estate Properties [Line Items]            
Unrealized losses on rental properties held for sale   (15,700)        
Book value   $ 11,300     $ 11,300  
Parsippany, Madison, Short Hills, Edison, And Red Bank, New Jersey [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member]            
Real Estate Properties [Line Items]            
Number of properties held for sale | property   6     6  
Number of disposal groups | item   3 6      
Accumulated depreciation   $ 169,031     $ 169,031  
Parsippany, Madison, Short Hills, Edison, And Red Bank, New Jersey [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Suburban Office Portfolio [Member]            
Real Estate Properties [Line Items]            
Accumulated depreciation   $ 161,040     $ 161,040  
Parsippany, Madison, Short Hills, Edison, And Red Bank, New Jersey [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Office [Member]            
Real Estate Properties [Line Items]            
Number of properties held for sale | property   16     16  
Unrealized losses on rental properties held for sale   $ (15,700)        
Number of properties not expected to recover from estimated net sales proceeds | property   6        
Land and other impairments   $ 9,500        
Parsippany, Madison, Short Hills, Edison, And Red Bank, New Jersey [Member] | Discontinued Operations [Member]            
Real Estate Properties [Line Items]            
Unrealized losses on rental properties held for sale   (14,000)        
Land and other impairments   $ 9,500        
Parsippany, New Jersey [Member]            
Real Estate Properties [Line Items]            
Number of properties held for sale | item   2     2  
Holmdel, New Jersey [Member] | Disposal Group, Not Discontinued Operations [Member] | Suburban Office Portfolio [Member]            
Real Estate Properties [Line Items]            
Area of property (in square feet) | ft²   350,000     350,000  
Accumulated depreciation   $ 10,500     $ 10,500  
Book value   19,800     19,800  
Reversal of valuation allowance   $ 2,800     $ 2,800  
Fort Lee, Parsippany, Madison, Short Hills, Edison, Red Bank, Florham Park [Member]            
Real Estate Properties [Line Items]            
Unrealized losses on rental properties held for sale     $ (174,100)      
Fort Lee, Parsippany, Madison, Short Hills, Edison, Red Bank, Florham Park [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member]            
Real Estate Properties [Line Items]            
Number of properties held for sale | property     21      
Accumulated depreciation     $ 412,785      
Fort Lee, Parsippany, Madison, Short Hills, Edison, Red Bank, Florham Park [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Suburban Office Portfolio [Member]            
Real Estate Properties [Line Items]            
Accumulated depreciation     401,212      
Fort Lee, Parsippany, Madison, Short Hills, Edison, Red Bank, Florham Park [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Office [Member]            
Real Estate Properties [Line Items]            
Number of disposal groups | item   6        
Fort Lee, Parsippany, Madison, Short Hills, Edison, Red Bank, Florham Park [Member] | Discontinued Operations [Member]            
Real Estate Properties [Line Items]            
Unrealized losses on rental properties held for sale     (137,900)      
Land and other impairments     $ 32,400