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
6 Months Ended
Jun. 30, 2017
USD ($)
ft²
property
Real Estate Properties [Line Items]  
Unrealized losses on rental properties held for sale $ (45,746)
Disposal Group, Held-for-sale, Not Discontinued Operations [Member]  
Real Estate Properties [Line Items]  
Assets held for sale, Deferred charges and other assets 13,800
Assets held for sale, Unbilled rents receivable, net 10,900
Assets held for sale, Accounts payable, accrued expenses and other liabilities 4,200
Expected assets to be written off 23,400
Expected liabilities to be written off $ 600
East Brunswick, 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 4
Number of properties held for sale | property 50
Estimated expected sales proceeds $ 372,000
Number of properties not epected to recover from estimated net sales proceeds | property 9