Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $) Share data in Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Consolidated Statements of Cash Flows [Abstract]
Net cash flow provided by operating activities:	$ 33,858,000	$ 57,632,000
Cash flow from investing activities:
Proceeds from disposition of real estate	17,114,000	11,659,000
Real estate developed or acquired, net of liabilities assumed	(83,797,000)	(43,062,000)
Equity contributions to joint ventures	(3,749,000)	(832,000)
Repayments of joint venture advances, net	25,000	22,516,000
Distributions of proceeds from sale and refinancing of joint venture interests		1,656,000
Return of investments in joint ventures	2,801,000	2,072,000
Issuance of notes receivable	(75,000)	(373,000)
Decrease in restricted cash - capital improvements	2,971,000	2,878,000
Net cash flow used for investing activities	(64,710,000)	(3,486,000)
Cash flow from financing activities:
Repayments of revolving credit facilities, net	(67,898,000)	(242,766,000)
Proceeds from issuance of senior notes, net of underwriting commissions and offering expenses of $350 in 2011		295,495,000
Repayment of senior notes	(187,670,000)
Proceeds from mortgages and other secured debt	353,506,000	121,861,000
Repayment of term loans and mortgage debt	(52,360,000)	(268,012,000)
Payment of debt issuance costs	(2,258,000)	(1,471,000)
Proceeds from issuance of common shares, net of underwriting commissions and offering expenses	(101,000)	(106,000)
Proceeds from issuance of common shares related to the exercise of warrants		59,979,000
Repurchase of common shares in conjunction with equity award plans	(1,447,000)	(1,626,000)
Contributions from non-controlling interests	93,000	94,000
Distributions to non-controlling interests and redeemable operating partnership units	(6,553,000)	(374,000)
Dividends paid	(29,128,000)	(15,692,000)
Net cash flow provided by (used for) financing activities	6,184,000	(52,618,000)
Cash and cash equivalents
(Decrease) increase in cash and cash equivalents	(24,668,000)	1,528,000
Effect of exchange rate changes on cash and cash equivalents	(450,000)	81,000
Cash and cash equivalents, beginning of period	41,206,000	19,416,000
Cash and cash equivalents, end of period	16,088,000	21,025,000
Supplemental disclosure of non-cash investing and financing activities:
Dividends payable	40,300,000	18,400,000
Increase to investments in and advances to joint ventures due to acquisition of partners' interests		6,800,000
Increase in net real estate assets		36,600,000
Mortgages assumed of previously unconsolidated joint ventures		50,100,000
Common shares issued due to the exercise of warrants		10
Equity derivative liability affiliate		$ 74,300,000