Disclosure Of Fair Value Of Assets And Liabilities (Narrative) (Details)	12 Months Ended
	Dec. 31, 2018 USD ($) property item	Dec. 31, 2017 USD ($) property
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value of Company's long-term debt	$ 2,711,712,000	$ 2,764,033,000
Principal balance outstanding	2,792,651,000	2,809,568,000
Aggregate carrying value	108,848,000	171,578,000
Land impairments	24,566,000
Office [Member] | Fort Lee, Newark, Paramus, Bridgewater, Morris Plains And Rahway, New Jersey [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Unrealized losses on rental properties held for sale	20,100,000
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Parsippany, Paramus, Rochelle Park, Hamilton And Wall, New Jersey And White Plains, New York [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Aggregate carrying value		$ 171,578,000
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Fort Lee, Newark, Paramus, Bridgewater, Morris Plains And Rahway, New Jersey [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Aggregate carrying value	$ 108,848,000
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Office [Member] | Parsippany, Paramus, Rochelle Park, Hamilton And Wall, New Jersey And White Plains, New York [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Number of properties held for sale | property		21
Aggregate carrying value		$ 171,600,000
Estimated expected sales proceeds		$ 223,000,000
Number of properties not expected to recover from estimated net sales proceeds | property		7
Unrealized losses on rental properties held for sale		$ 12,300,000
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Office [Member] | Fort Lee, Newark, Paramus, Bridgewater, Morris Plains And Rahway, New Jersey [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Number of properties held for sale | property	6
Aggregate carrying value	$ 108,800,000
Estimated expected sales proceeds	$ 124,000,000
Number of properties not expected to recover from estimated net sales proceeds | property	4
Unrealized losses on rental properties held for sale	$ 20,100,000
Number of real estate properties | item	159
Disposal Group, Not Discontinued Operations [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Unrealized losses on rental properties held for sale	$ (20,135,000)	$ (12,331,000)