Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $) Share data in Millions	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010
Condensed Consolidated Statements of Cash Flows [Abstract]
Net cash flow provided by operating activities:	$ 133,904,000	$ 127,981,000
Cash flow from investing activities:
Real estate developed or acquired, net of liabilities assumed	(68,595,000)	(75,804,000)
Equity contributions to joint ventures	(7,068,000)	(18,497,000)
Repayments of (advances to) joint venture advances, net	23,130,000	(108,000)
Distributions of proceeds from sale and refinancing of joint venture interests	14,033,000	3,567,000
Return on investments in joint ventures	5,541,000	14,761,000
Repayment (issuance) of notes receivable, net	13,934,000	(4,550,000)
Decrease in restricted cash	217,000	60,199,000
Proceeds from disposition of real estate	70,883,000	65,682,000
Net cash flow provided by investing activities	52,075,000	45,250,000
Cash flow from financing activities:
Repayments of revolving credit facilities, net	(115,908,000)	(113,007,000)
Repayment of senior notes	(93,038,000)	(389,924,000)
Proceeds from issuance of senior notes, net of underwriting commissions and offering expenses of $350 and $400 in 2011 and 2010, respectively	295,495,000	296,785,000
Proceeds from mortgages and other secured debt	121,956,000	4,327,000
Repayment on term loans and mortgage debt	(362,904,000)	(325,278,000)
Payment of debt issuance costs	(9,394,000)	(2,309,000)
Proceeds from issuance of common shares, net of underwriting commissions and issuance costs of $686 in 2011 and $524 in 2010	129,939,000	382,755,000
Proceeds from issuance of common shares related to the exercise of warrants	59,873,000
Redemption of preferred shares	(180,000,000)
(Purchase of) proceeds from the issuance of common shares in conjunction with equity award plans	(979,000)	90,000
Contributions from non-controlling interests	187,000	328,000
Distributions to non-controlling interests and redeemable operating partnership units	(1,269,000)	(2,017,000)
Dividends paid	(34,102,000)	(30,153,000)
Net cash flow used for financing activities	(190,144,000)	(178,403,000)
Cash and cash equivalents
Decrease in cash and cash equivalents	(4,165,000)	(5,172,000)
Effect of exchange rate changes on cash and cash equivalents	174,000	(80,000)
Cash and cash equivalents, beginning of period	19,416,000	26,172,000
Cash and cash equivalents, end of period	15,425,000	20,920,000
Dividend payable	18,000,000	12,000,000
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	10.0
Reclassification of equity derivative liability-affiliate	74,300,000
Noncash dividend to net income available for common stockholders	6,400,000
Reduction in real estate assets		28,700,000
Decrease in Non-controlling Interests Due To Adoption of ASC 810		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