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Debt (Summary Of Debt Outstanding) (Details) - USD ($)	Dec. 31, 2015	Sep. 28, 2015	Mar. 16, 2015	Dec. 31, 2014	Nov. 14, 2014
Debt Instrument [Line Items]
Mortgages payable	$ 482,822,000			$ 563,698,000
Notes payable	343,600,000			290,519,000
Senior notes and debentures	1,744,324,000			1,483,813,000
Capital lease obligations	71,620,000			71,647,000
Total debt and capital lease obligations	2,642,366,000			2,409,677,000
Mortgages Payable
Debt Instrument [Line Items]
Principal balance	471,994,000			554,865,000
Net unamortized premium (discount)	10,828,000			8,833,000
Notes Payable
Debt Instrument [Line Items]
Notes payable	343,600,000			290,519,000
Senior Notes and Debentures
Debt Instrument [Line Items]
Principal balance	1,744,200,000			1,494,200,000
Net unamortized premium (discount)	124,000			(10,387,000)
Barracks Road \| Mortgages Payable
Debt Instrument [Line Items]
Principal balance	$ 0			35,985,000
Interest rate	7.95%
Hauppauge \| Mortgages Payable
Debt Instrument [Line Items]
Principal balance	$ 0			13,566,000
Interest rate	7.95%
Lawrence Park \| Mortgages Payable
Debt Instrument [Line Items]
Principal balance	$ 0			25,507,000
Interest rate	7.95%
Wildwood \| Mortgages Payable
Debt Instrument [Line Items]
Principal balance	$ 0			22,420,000
Interest rate	7.95%
Wynnewood \| Mortgages Payable
Debt Instrument [Line Items]
Principal balance	$ 0			25,994,000
Interest rate	7.95%
Brick Plaza \| Mortgages Payable
Debt Instrument [Line Items]
Principal balance	$ 0			26,415,000
Interest rate	7.42%
Plaza El Segundo \| Mortgages Payable
Debt Instrument [Line Items]
Principal balance	$ 175,000,000			175,000,000
Interest rate	6.33%
The Grove at Shrewsbury (East) \| Mortgages Payable
Debt Instrument [Line Items]
Principal balance	$ 43,557,000			44,519,000
Interest rate	5.82%
The Grove at Shrewsbury (West) \| Mortgages Payable
Debt Instrument [Line Items]
Principal balance	$ 11,024,000			11,242,000
Interest rate	6.38%
Rollingwood Apartments \| Mortgages Payable
Debt Instrument [Line Items]
Principal balance	$ 21,716,000			22,130,000
Interest rate	5.54%
The Shops at Sunset Place \| Mortgages Payable
Debt Instrument [Line Items]
Principal balance	$ 70,542,000			0
Interest rate	5.624%
29th Place \| Mortgages Payable
Debt Instrument [Line Items]
Principal balance	$ 4,753,000			4,941,000
Interest rate	5.91%
THE AVENUE at White Marsh \| Mortgages Payable
Debt Instrument [Line Items]
Principal balance	$ 52,705,000			52,705,000
Interest rate	3.35%
Montrose Crossing \| Mortgages Payable
Debt Instrument [Line Items]
Principal balance	$ 74,329,000			75,867,000
Interest rate	4.20%
Brook 35 \| Mortgages Payable
Debt Instrument [Line Items]
Principal balance	$ 11,500,000			11,500,000
Interest rate	4.65%
Chelsea \| Mortgages Payable
Debt Instrument [Line Items]
Principal balance	$ 6,868,000			7,074,000
Interest rate	5.36%
Escondido Promenade \| Notes Payable
Debt Instrument [Line Items]
Interest rate	0.03%
Municipal bond	$ 9,400,000			9,400,000
Revolving credit facility \| Notes Payable
Debt Instrument [Line Items]
Revolving credit facility	$ 53,500,000			0
Term Loan \| Notes Payable
Debt Instrument [Line Items]
Other Notes Payable				275,000,000
Various \| Notes Payable
Debt Instrument [Line Items]
Interest rate	11.31%
Other Notes Payable	$ 5,700,000			6,119,000
6.20% notes \| Senior Notes and Debentures
Debt Instrument [Line Items]
Principal balance	$ 0			200,000,000
Interest rate	6.20%
5.90% notes \| Senior Notes and Debentures
Debt Instrument [Line Items]
Principal balance	$ 150,000,000			150,000,000
Interest rate	5.90%
2.55% notes \| Senior Notes and Debentures
Debt Instrument [Line Items]
Principal balance	$ 250,000,000	$ 250,000,000		0
Interest rate	2.55%	2.55%
3.00% notes \| Senior Notes and Debentures
Debt Instrument [Line Items]
Principal balance	$ 250,000,000			250,000,000
Interest rate	3.00%
2.75% notes \| Senior Notes and Debentures
Debt Instrument [Line Items]
Principal balance	$ 275,000,000			275,000,000
Interest rate	2.75%
3.95% notes \| Senior Notes and Debentures
Debt Instrument [Line Items]
Principal balance	$ 300,000,000			300,000,000
Interest rate	3.95%
7.48% debentures \| Senior Notes and Debentures
Debt Instrument [Line Items]
Principal balance	$ 29,200,000			29,200,000
Interest rate	7.48%
6.82% medium term notes \| Senior Notes and Debentures
Debt Instrument [Line Items]
Principal balance	$ 40,000,000			40,000,000
Interest rate	6.82%
4.50% notes \| Senior Notes and Debentures
Debt Instrument [Line Items]
Principal balance	$ 450,000,000		$ 200,000,000	$ 250,000,000	$ 250,000,000
Interest rate	4.50%		4.50%