Quarterly report pursuant to Section 13 or 15(d)

Recent Transactions (Rental Property Held for Sale, Net) (Narrative) (Details)

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Recent Transactions (Rental Property Held for Sale, Net) (Narrative) (Details)
$ in Thousands
 3 Months Ended 9 Months Ended
Sep. 30, 2018
USD ($)
ft²
item
property
Sep. 30, 2018
USD ($)
ft²
item
property
Real Estate Properties [Line Items]    
Number of units | item 1,153 1,153
Paramus, Bridgewater, Rochelle Park, Morris Plains and Rahway, New Jersey [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member]    
Real Estate Properties [Line Items]    
Unrealized losses on properties held for sale $ 20,135 $ 20,135
Assets held for sale, Deferred charges and other assets 2,700 2,700
Assets held for sale, Unbilled rents receivable, net 1,000 1,000
Assets held for sale, Accounts payable, accrued expenses and other liabilities $ 2,400 2,400
Expected assets to be written off   3,000
Expected liabilities to be written off   $ 1,600
Paramus, Bridgewater, Rochelle Park, Morris Plains and Rahway, New Jersey [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Office [Member]    
Real Estate Properties [Line Items]    
Area of property (in square feet) | ft² 680,000 680,000
Number of properties held for sale | property 4 4
Unrealized loss allowance $ 19,600  
Estimated expected sales proceeds   $ 85,500
Number of units | item 159 159