Debt (Parentheticals) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended			0 Months Ended		3 Months Ended				0 Months Ended	3 Months Ended					1 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2012 Notes And Mortgages Payable Fixed Rate [Member]	Jan. 09, 2012 Notes And Mortgages Payable Fixed Rate [Member] New York 350 Park Avenue [Member]	Mar. 31, 2012 Notes And Mortgages Payable Fixed Rate [Member] New York 350 Park Avenue [Member]	Mar. 31, 2012 Notes And Mortgages Payable Fixed Rate [Member] Washington DC Skyline Place [Member]	Mar. 31, 2012 Notes And Mortgages Payable Fixed Rate [Member] Washington DC River House Apartments [Member]	Mar. 31, 2012 Notes And Mortgages Payable Fixed Rate [Member] Retail Cross Collateralized Mortgages On 40 Strip Shopping Centers [Member]	Mar. 31, 2012 Notes And Mortgages Payable Variable Rate [Member]	Mar. 05, 2012 Notes And Mortgages Payable Variable Rate [Member] New York 100 West 33rd Street - Office & Retail [Member]	Mar. 31, 2012 Notes And Mortgages Payable Variable Rate [Member] New York 100 West 33rd Street - Office & Retail [Member]	Mar. 31, 2012 Notes And Mortgages Payable Variable Rate [Member] New York 435 Seventh Avenue [Member]	Mar. 31, 2012 Notes And Mortgages Payable Variable Rate [Member] Washington DC River House Apartments [Member]	Mar. 31, 2012 Notes And Mortgages Payable Variable Rate [Member] Retail Beverly Connection [Member]	Mar. 31, 2012 Notes And Mortgages Payable Variable Rate [Member] Retail Cross Collateralized Mortgages On 40 Strip Shopping Centers [Member]	Apr. 30, 2012 Exchangeable And Convertible Senior Debentures [Member] Subsequent Event [Member]
Interest Rate, End of Period			5.44%		3.75%	5.74%	5.43%	4.21%	2.48%		2.74%	5.00%	1.60%	4.75%	2.36%
Notes And Loans Payable Refinanced Amount				$ 300,000						$ 325,000
Debt Amortization Period				30 years
Debt Term				5 years						3 years
Number Of Extensions Available										2
Length Of Extension Available In Years										1 year
Repayments of borrowings	884,679	1,197,312		132,000
Vacancy Rate						26.00%
Spread Over LIBOR										2.50%	2.50%	3.00%	1.53%	4.25%	1.36%
Debt Instrument, Description of Variable Rate Basis										LIBOR	LIBOR	LIBOR	Freddie Mac	LIBOR	LIBOR
Retained Proceeds From Refinancing										87,000
LIBOR Floor												2.00%		0.50%	1.00%
Repayments of Convertible Debt																$ 510,215