Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $) Share data in Millions	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010
Condensed Consolidated Statements of Cash Flows [Abstract]
Net cash flow provided by operating activities:	$ 224,710,000	$ 211,038,000
Cash flow from investing activities:
Proceeds from disposition of real estate	126,641,000	120,671,000
Real estate developed or acquired, net of liabilities assumed	(146,155,000)	(123,808,000)
Equity contributions to joint ventures	(7,501,000)	(24,999,000)
Repayments of joint venture advances, net	23,075,000	28,000
Distributions of proceeds from sale and refinancing of joint venture interests	21,502,000	5,109,000
Return of Investments in joint ventures	8,110,000	19,084,000
Repayment (issuance) of notes receivable, net	4,007,000	(62,848,000)
Decrease in restricted cash	279,000	76,075,000
Net cash flow provided by investing activities:	29,958,000	9,312,000
Cash flow from financing activities:
Repayments of revolving credit facilities, net	(54,598,000)	(286,697,000)
Repayment of senior notes	(185,566,000)	(539,127,000)
Proceeds from issuance of senior notes, net of underwriting commissions and offering expenses of $350 and $843 in 2011 and 2010, respectively	295,495,000	590,710,000
Proceeds from mortgages and other secured debt	186,956,000	4,460,000
Repayment of term loans and mortgage debt	(423,264,000)	(384,151,000)
Payment of debt issuance costs	(11,121,000)	(2,537,000)
Proceeds from issuance of common shares, net of underwriting commissions and issuance costs of $686 in 2011 and $956 in 2010	129,792,000	440,472,000
Proceeds from issuance of common shares related to the exercise of warrants	59,873,000
Redemption of preferred shares	(180,000,000)
Purchase of common shares in conjunction with equity award plans	(6,111,000)	(630,000)
Contributions from non-controlling interests	281,000	486,000
Distributions to non-controlling interests and redeemable operating partnership units	(1,677,000)	(2,382,000)
Dividends paid	(63,238,000)	(45,722,000)
Net cash flow used for financing activities	(253,178,000)	(225,118,000)
Cash and cash equivalents
Decrease in cash and cash equivalents	1,490,000	(4,768,000)
Effect of exchange rate changes on cash and cash equivalents	(225,000)	(69,000)
Cash and cash equivalents, beginning of period	19,416,000	26,172,000
Cash and cash equivalents, end of period	20,681,000	21,335,000
Dividend payable	23,600,000	12,000,000
Real estate assets acquired	107,200,000
Accounts receivable, intangible assets and other assets acquired	13,400,000
Debt assumed to acquire assets	67,000,000
Accounts payable and other liabilities for acquiring assets	9,200,000
Increase to investments in and advances to joint ventures	7,800,000	8,400,000
Increase in net real estate assets	34,800,000
Loans assumed	50,100,000
Common shares issued due to exercise of warrants	10
Reclassification of equity derivative liability-affiliate	74,300,000
Write-off of original preferred share issuance costs	(6,402,000)
Reduction in real estate assets		28,700,000
Decrease in Non-controlling interests		12,400,000
Increase to accumulated distributions in excess of net income		7,800,000
Increase in real estate assets		19,000,000
Decrease in notes receivable		19,000,000
Decrease in real estate assets net due to deconsolidation of assets	14,000,000	156,300,000
Decrease in restricted cash due to deconsolidation of assets		5,200,000
Decrease in Mortgages Payable due to deconsolidation of assets	18,300,000	166,700,000
Increase in non-controlling interests due to deconsolidation of assets		$ 3,900,000