Mortgage and Other Indebtedness (Details) (USD $) In Thousands, unless otherwise specified					9 Months Ended					3 Months Ended	9 Months Ended			3 Months Ended
	Nov. 30, 2012	Sep. 30, 2012	Dec. 31, 2011		Sep. 30, 2012 Secured Line of Credit 1 [Member]		Sep. 30, 2012 Secured Line of Credit 2 [Member]	Sep. 30, 2012 Secured Line of Credit 3 [Member]	Sep. 30, 2012 Unsecured lines of credit [Member]	Sep. 30, 2012 Unsecured Line of Credit 2 [Member]	Sep. 30, 2012 Unsecured Line of Credit 2 [Member]	Nov. 30, 2012 Unsecured Line of Credit 2 [Member]	Sep. 30, 2012 Letter of Credit [Member]	Sep. 30, 2012 Secured Lines of Credit [Member]	Sep. 30, 2012 Unsecured Term Loans[Member]	Sep. 30, 2012 Fixed-Rate Debt [Member]	Dec. 31, 2011 Fixed-Rate Debt [Member]		Sep. 30, 2012 Fixed-Rate Debt [Member] Non-recourse Loans on Operating Properties [Member]		Dec. 31, 2011 Fixed-Rate Debt [Member] Non-recourse Loans on Operating Properties [Member]		Sep. 30, 2012 Fixed-Rate Debt [Member] Recourse Term Loans on Operating Properties [Member]		Dec. 31, 2011 Fixed-Rate Debt [Member] Recourse Term Loans on Operating Properties [Member]		Sep. 30, 2012 Variable-Rate Debt [Member]	Dec. 31, 2011 Variable-Rate Debt [Member]		Sep. 30, 2012 Variable-Rate Debt [Member] Construction Loans [Member]	Dec. 31, 2011 Variable-Rate Debt [Member] Construction Loans [Member]		Sep. 30, 2012 Variable-Rate Debt [Member] Secured Lines of Credit [Member]	Dec. 31, 2011 Variable-Rate Debt [Member] Secured Lines of Credit [Member]		Sep. 30, 2012 Variable-Rate Debt [Member] Unsecured Term Loans[Member]	Dec. 31, 2011 Variable-Rate Debt [Member] Unsecured Term Loans[Member]		Sep. 30, 2012 Variable-Rate Debt [Member] Recourse Term Loans on Operating Properties [Member]		Dec. 31, 2011 Variable-Rate Debt [Member] Recourse Term Loans on Operating Properties [Member]		Sep. 30, 2012 Variable-Rate Debt [Member] Non Recourse Term Loans On Operating Properties [Member]		Dec. 31, 2011 Variable-Rate Debt [Member] Non Recourse Term Loans On Operating Properties [Member]		Sep. 30, 2012 Interest Rate Swap [Member]
Debt Instrument [Line Items]
Debt Instrument, Number of Instruments														3	2																																4
Line of Credit Facility, Maximum Borrowing Capacity	$ 1,200,000				$ 525,000	[1]	$ 105,000	$ 520,000		$ 228,000	$ 228,000	$ 600,000	$ 50,000																				$ 1,150,000
Line of Credit Facility, Amount Outstanding		167,209			77,500	[1]	29,205	150,196	167,209	228,000	228,000
Total Outstanding																3,822,271	3,733,355		3,772,111	[2]	3,656,243	[2]	50,160		77,112		879,119	756,000		31,246	25,921		256,901	27,300		395,209	409,590		71,513		124,439		124,250		168,750
Weighted Average Interest Rate (in hundredths)		4.84%	4.99%	[3]					1.35%	1.84%	1.84%			2.70%		5.43%	5.54%	[3]	5.43%	[3]	5.55%	[3]	5.83%	[3]	5.89%	[3]	2.25%	2.18%	[3]	3.28%	3.25%	[3]		3.03%	[3]	1.63%	1.67%	[3]	2.07%	[3]	2.29%	[3]	3.33%	[3]	3.03%	[3]
Mortgage and other indebtedness		4,701,390	4,489,355
Debt Instrument, Maturity Date					Feb. 26, 2014		Jun. 01, 2015	Apr. 28, 2014	Nov. 30, 2012	Nov. 01, 2016	Apr. 22, 2013
Interest Rate Terms							LIBOR plus a margin ranging from 1.75% to 2.75%		LIBOR plus a margin ranging from 0.95% to 1.40%		LIBOR plus a margin ranging from 1.50% to 1.80%
Line of credit, extended maturity date					Feb. 26, 2015		Jun. 01, 2016
Fees on amount of unused availability of secured lines of credit, maximum (in hundredths)														0.35%
Fees on amount of unused availability of secured lines of credit, minimum (in hundredths)														0.15%
Letters of Credit Outstanding, Amount					351	[1]							1,475
Additional secured and unsecured lines of credit with commitment													14,000
Covenants and Restrictions [Abstract]
Minimum loan amount in default payment for recourse loan		50,000
Minimum loan amount in default payment for non-recourse loan		$ 100,000

[1] There was an additional $351 outstanding on this secured line of credit as of September 30, 2012 forletters of credit. Up to $50,000 of the capacity on this line can be used for letters of credit.

[2] The Company has four interest rate swaps on notional amounts totaling $114,884 as of September 30, 2012 and $117,700 as of December 31, 2011 related to four variable-rate loans on operating properties to effectively fix the interest rate on the respective loans. Therefore, these amounts are reflected in fixed-rate debt at September 30, 2012 and December 31, 2011.

[3] Weighted-average interest rate includes the effect of debt premiums (discounts), but excludes amortization of deferred financing costs.