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) - Paramus And Rochelle Park [Member] - Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
$ in Millions
3 Months Ended
Mar. 31, 2018
USD ($)
ft²
property
Real Estate Properties [Line Items]  
Assets held for sale, Deferred charges and other assets $ 2.7
Assets held for sale, Unbilled rents receivable, net 0.4
Assets held for sale, Accounts payable, accrued expenses and other liabilities 1.6
Expected assets to be written off 2.6
Expected liabilities to be written off $ 0.9
Office [Member]  
Real Estate Properties [Line Items]  
Area of property (in square feet) | ft² 400,000
Number of properties held for sale | property 2
Estimated expected sales proceeds $ 41.4