Quarterly report pursuant to Section 13 or 15(d)

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

v3.20.1
Recent Transactions (Real Estate Held For Sale/Discontinued Operations/Dispositions) (Narrative) (Details)
$ in Thousands
 3 Months Ended 15 Months Ended
Mar. 31, 2020
USD ($)
property
item
Mar. 31, 2020
USD ($)
property
Mar. 31, 2020
ft²
Mar. 31, 2020
item
Dec. 19, 2019
ft²
Real Estate Properties [Line Items]          
Unrealized losses on rental properties held for sale $ (7,915)        
Land and other Impairments $ 5,263        
Suburban Office Portfolio [Member]          
Real Estate Properties [Line Items]          
Area of property (in square feet) | ft²         6,600,000
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Suburban Office Portfolio [Member]          
Real Estate Properties [Line Items]          
Number of real estate properties 34 34   12  
Area of property (in square feet) | ft²     5,900,000    
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Office [Member]          
Real Estate Properties [Line Items]          
Number of properties held for sale | property 34 34      
Number of disposal groups | property 12        
Disposal Group, Not Discontinued Operations [Member]          
Real Estate Properties [Line Items]          
Unrealized losses on rental properties held for sale $ (45,068)        
Area Of Real Estate Property Sold | ft²     200,000    
Gain (loss) on sale of property $ 17,322        
Disposal Group, Not Discontinued Operations [Member] | Properties Disposed One [Member] | Suburban Office Portfolio [Member]          
Real Estate Properties [Line Items]          
Area of property (in square feet) | ft²     697,000    
Number of properties sold | property   3      
Gain (loss) on sale of property   $ 87,200      
Disposal Group, Not Discontinued Operations [Member] | Properties Disposed Two [Member]          
Real Estate Properties [Line Items]          
Number of real estate properties | property 17 17      
Area of property (in square feet) | ft²     2,500,000    
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 17 17      
Area of property (in square feet) | ft²     2,500,000    
Gain (loss) on sale of property $ 335,500        
Parsippany, Madison, Short Hills, Edison, Red Bank, and Florhan Park [Member]          
Real Estate Properties [Line Items]          
Unrealized losses on rental properties held for sale 53,000        
Land and other Impairments $ 5,300        
Parsippany, Madison, Short Hills, Edison, Red Bank, and Florhan Park [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member]          
Real Estate Properties [Line Items]          
Number of properties held for sale | property 20 20      
Number of disposal groups | item 4        
Parsippany, Madison, Short Hills, Edison, Red Bank, and Florhan Park [Member] | Discontinued Operations [Member]          
Real Estate Properties [Line Items]          
Unrealized losses on rental properties held for sale $ 45,100        
Land and other Impairments $ 5,300