Quarterly report pursuant to Section 13 or 15(d)

Recent Transactions (Dispositions/Rental Property Held For Sale) (Narrative) (Details)

v3.19.3
Recent Transactions (Dispositions/Rental Property Held For Sale) (Narrative) (Details)
1 Months Ended 3 Months Ended 9 Months Ended
Oct. 23, 2019
USD ($)
Oct. 03, 2019
USD ($)
Sep. 20, 2019
USD ($)
Apr. 30, 2019
USD ($)
Oct. 31, 2019
USD ($)
property
Sep. 30, 2019
USD ($)
Sep. 30, 2019
USD ($)
property
item
Sep. 30, 2018
USD ($)
Sep. 30, 2019
item
Sep. 30, 2019
ft²
Sep. 30, 2019
property
Real Estate Properties [Line Items]                      
Payment for borrowings             $ 398,000,000 $ 381,000,000      
Subsequent Event [Member] | Overlook Ridge Agreement [Member]                      
Real Estate Properties [Line Items]                      
Payment for borrowings $ 235,800,000                    
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Rockpoint [Member] | Subsequent Event [Member] | Overlook Ridge Agreement [Member] | Chase and Alterra At Overlook Ridge Properties [Member]                      
Real Estate Properties [Line Items]                      
Sales proceeds   $ 411,500,000                  
Disposal Group, Not Discontinued Operations [Member]                      
Real Estate Properties [Line Items]                      
Unrealized losses on rental properties held for sale             (35,079,000)        
Sales proceeds             593,436,000        
Gain (loss) on sale of property             $ 268,364,000        
Number of building sold | item             63        
Malden, MA [Member] | Disposal Group, Not Discontinued Operations [Member]                      
Real Estate Properties [Line Items]                      
Sales proceeds       $ 685,000              
Gain (loss) on sale of property       $ 270,000              
Revere, MA [Member] | Disposal Group, Not Discontinued Operations [Member]                      
Real Estate Properties [Line Items]                      
Sales proceeds     $ 1,185,000                
Gain (loss) on sale of property     $ 296,000                
Fort Lee, Parsippany, Hanover And Neptune, New Jersey, And Malden And Revere, Massachusetts [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member]                      
Real Estate Properties [Line Items]                      
Unrealized losses on rental properties held for sale           $ 35,100,000          
Estimated expected sales proceeds             $ 536,600,000        
Assets held for sale, Deferred charges and other assets           7,200,000 7,200,000        
Assets held for sale, Unbilled rents receivable, net           5,500,000 5,500,000        
Assets held for sale, Accounts payable, accrued expenses and other liabilities           $ 3,600,000 3,600,000        
Expected assets to be written off             11,500,000        
Expected liabilities to be written off             $ 700,000        
Number of properties not expected to recover from estimated net sales proceeds | property             2        
Fort Lee, Parsippany, Hanover And Neptune, New Jersey, And Malden And Revere, Massachusetts [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Office [Member]                      
Real Estate Properties [Line Items]                      
Area of property (in square feet) | ft²                   697,000  
Number of properties held for sale | property                     3
Fort Lee, Parsippany, Hanover And Neptune, New Jersey, And Malden And Revere, Massachusetts [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Multi-Family Properties [Member]                      
Real Estate Properties [Line Items]                      
Number of properties held for sale                 1,386   3
Fort Lee, Parsippany, Hanover And Neptune, New Jersey, And Malden And Revere, Massachusetts [Member] | Disposal Group, Not Discontinued Operations [Member] | Office [Member] | Subsequent Event [Member]                      
Real Estate Properties [Line Items]                      
Sales proceeds         $ 433,000,000            
Number of building sold | property         1            
Fort Lee, Parsippany, Hanover And Neptune, New Jersey, And Malden And Revere, Massachusetts [Member] | Disposal Group, Not Discontinued Operations [Member] | Multi-Family Properties [Member] | Subsequent Event [Member]                      
Real Estate Properties [Line Items]                      
Number of building sold | property         3