Debt Of The Operating Partnership (Debt Maturities Table) (Details) (USD $)			12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2011 Revolving Credit Facility [Member] years	Dec. 31, 2011 Global Revolving Credit Facility [Member]	Dec. 31, 2011 Unsecured Senior Notes [Member]	Dec. 31, 2011 Senior Notes [Member]	Dec. 31, 2010 Senior Notes [Member]	Dec. 31, 2011 Exchangeable Senior Debentures [Member]	Dec. 31, 2010 Exchangeable Senior Debentures [Member]	Dec. 31, 2011 Mortgage Loans [Member]	Dec. 31, 2010 Mortgage Loans [Member]	Dec. 31, 2011 Other Secured Loans [Member]	Dec. 31, 2010 Other Secured Loans [Member]
Debt of the Operating Partnership [Line Items]
2012	$ 156,723,000									$ 156,723,000
2013	244,635,000				33,000,000					201,135,000		10,500,000
2014	481,430,000							266,400,000		215,030,000
2015	792,332,000			275,106,000	67,000,000	375,000,000				75,226,000
2016	211,191,000				25,000,000					186,191,000
Thereafter	1,060,750,000				50,000,000	900,000,000				110,750,000
Subtotal	2,947,061,000			275,106,000	175,000,000	1,275,000,000		266,400,000		945,055,000		10,500,000
Unamortized discount	(8,928,000)					(8,928,000)	(8,970,000)		(1,456,000)
Unamortized net premium	2,077,000									2,077,000	1,101,000
Global Revolving credit facilities	275,106,000	333,534,000		275,106,000
Unsecured Senior Notes	2,947,061,000			275,106,000	175,000,000	1,275,000,000		266,400,000		945,055,000		10,500,000
Senior Notes						1,266,072,000	866,030,000
Exchangeable Senior Debenture	266,400,000	353,702,000						266,400,000	353,702,000
Mortgage loans	947,132,000	1,043,188,000								947,132,000	1,043,188,000
Other secured loan	10,500,000	10,500,000										10,500,000	10,500,000
Total indebtedness	2,940,210,000	2,806,954,000
Revolving credit facility commitments extension (years)			1
Limited recourse guarantees										55,000,000
Partial letter of credit										$ 36,200,000