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, ft² in Millions
9 Months Ended
Sep. 30, 2017
USD ($)
ft²
property
Real Estate Properties [Line Items]  
Unrealized losses on rental properties held for sale $ (25,744)
Parsippany, Woodcliff Lake, Paramus And Rochelle Park, New Jersey [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member]  
Real Estate Properties [Line Items]  
Assets held for sale, Deferred charges and other assets 7,500
Assets held for sale, Unbilled rents receivable, net 3,900
Assets held for sale, Accounts payable, accrued expenses and other liabilities 3,100
Expected assets to be written off 10,700
Expected liabilities to be written off $ 300
Parsippany, Woodcliff Lake, Paramus And Rochelle Park, 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 1.3
Number of properties held for sale | property 6
Estimated expected sales proceeds $ 132,000
Number of properties not epected to recover from estimated net sales proceeds | property 3