Mortgage and Other Indebtedness (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012		Dec. 31, 2011
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 1,150,000
Line of Credit Facility, Amount Outstanding	395,209
Weighted Average Interest Rate (in hundredths)			4.99%	[1]
Mortgage and other indebtedness	4,459,248		4,489,355
Interest Rate Terms	LIBOR plus a margin ranging from 1.50% to 1.80%
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
Secured Line of Credit 1 [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	525,000	[2]
Line of Credit Facility, Amount Outstanding	150,195
Secured Line of Credit 2 [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	105,000
Line of Credit Facility, Amount Outstanding	5,000
Secured Line of Credit 3 [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	520,000
Line of Credit Facility, Amount Outstanding	204,223	[2]
Letters of Credit Outstanding, Amount	2,169	[2]
Unsecured lines of credit [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Amount Outstanding	167,209
Weighted Average Interest Rate (in hundredths)	1.35%
Interest Rate Terms	LIBOR plus a margin ranging from 0.95% to 1.40%
Unsecured Line of Credit 2 [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	228,000
Line of Credit Facility, Amount Outstanding	228,000
Weighted Average Interest Rate (in hundredths)	1.85%
Line of Credit Maturity Date	Nov. 30, 2012
Number of Extension Options Available	1
Letter of Credit [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	50,000
Letters of Credit Outstanding, Amount	2,650
Additional secured and unsecured lines of credit with commitment	15,906
Secured Lines of Credit [Member]
Debt Instrument [Line Items]
Debt Instrument, Number of Instruments	3
Weighted Average Interest Rate (in hundredths)	3.00%
Interest Rate Terms	LIBOR plus an applicable spread, ranging from 2.00% to 3.00%
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%
Unsecured Term Loans[Member]
Debt Instrument [Line Items]
Debt Instrument, Number of Instruments	2
Fixed-Rate Debt [Member]
Debt Instrument [Line Items]
Total Outstanding	3,393,241		3,733,355
Weighted Average Interest Rate (in hundredths)			5.54%	[1]
Fixed-Rate Debt [Member] | Non-recourse Loans on Operating Properties [Member]
Debt Instrument [Line Items]
Total Outstanding	3,342,787	[3]	3,656,243	[3]
Weighted Average Interest Rate (in hundredths)	5.42%	[1]	5.55%	[1]
Fixed-Rate Debt [Member] | Recourse Term Loans on Operating Properties [Member]
Debt Instrument [Line Items]
Total Outstanding	50,454		77,112
Weighted Average Interest Rate (in hundredths)	5.83%	[1]	5.89%	[1]
Variable-Rate Debt [Member]
Debt Instrument [Line Items]
Total Outstanding	1,066,007		756,000
Weighted Average Interest Rate (in hundredths)			2.18%	[1]
Variable-Rate Debt [Member] | Construction Loans [Member]
Debt Instrument [Line Items]
Total Outstanding			25,921
Weighted Average Interest Rate (in hundredths)			3.25%	[1]
Variable-Rate Debt [Member] | Secured Lines of Credit [Member]
Debt Instrument [Line Items]
Total Outstanding	359,418		27,300
Weighted Average Interest Rate (in hundredths)			3.03%	[1]
Variable-Rate Debt [Member] | Unsecured Term Loans[Member]
Debt Instrument [Line Items]
Total Outstanding			409,590
Weighted Average Interest Rate (in hundredths)			1.67%	[1]
Variable-Rate Debt [Member] | Recourse Term Loans on Operating Properties [Member]
Debt Instrument [Line Items]
Total Outstanding	119,407		124,439
Weighted Average Interest Rate (in hundredths)	2.47%	[1]	2.29%	[1]
Variable-Rate Debt [Member] | Non Recourse Term Loans on Operating Properties [Member]
Debt Instrument [Line Items]
Total Outstanding	$ 163,750		$ 168,750
Weighted Average Interest Rate (in hundredths)	3.50%	[1]	3.03%	[1]

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

[2] There was an additional $2,169 outstanding on this secured line of credit as of March 31, 2012 forletters of credit. Up to $50,000 of the capacity on this line can be used for letters of credit.

[3] The Company has four interest rate swaps on notional amounts totaling $116,748 as of March 31, 2012 and $117,700 as of December 31, 2011 related to its 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 March 31, 2012 and December 31, 2011.