Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010
Condensed Consolidated Statements of Cash Flows (Unaudited) [Abstract]
Cash flows from operating activities:	$ 104,351	$ 89,414
Net Income	28,560	31,728
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on sale of real estate	(5,853)	0
Gain on sale of marketable securities	(4,543)	(9,041)
Loss (gain) on early retirement of debt	253	10
Equity income in co-investments excluding gain on sales of real estate	2,120	401
Amortization of discount on exchangeable bonds	0	41
Amortization of discount on marketable securities	(2,297)	(1,916)
Amortization of deferred interest from settlement of swaps	4,349	97
Amortization of discount on notes receivables	(878)	(363)
Depreciation	74,541	61,748
Amortization of deferred financing costs	1,443	1,628
Stock-based compensation	1,056	1,739
Prepaid expenses and other assets	(697)	(621)
Accounts payable and accrued liabilities	5,097	2,973
Other liabilities	1,200	990
Additions to real estate:
Acquisitions	(38,958)	(6,757)
Improvements to recent acquisitions	(11,804)	(725)
Redevelopment expenditures	(16,296)	(6,951)
Revenue generating capital expenditures	(1,220)	(358)
Non-revenue generating capital expenditures	(7,711)	(10,962)
Dispositions of real estate	15,972	0
Additions to real estate under development	(65,695)	(53,414)
Changes in restricted cash and refundable deposits	(3,210)	(5,733)
Purchases of marketable securities	(6,805)	(18,276)
Sales and maturities of marketable securities	27,997	65,919
Purchases of and advances under notes and other receivables	0	(21,227)
Collections of notes and other receivables	368	1,826
Contributions to co-investments	(43,207)	(66,498)
Distributions from co-investments	450	0
Net cash used in investing activities	(150,119)	(123,156)
Cash flows from financing activities:
Borrowings under mortgage notes payable, lines of credit and bonds	645,419	212,764
Repayment under mortgage notes payable, lines of credit and bonds	(661,193)	(163,817)
Additions to deferred charges	(1,441)	(623)
Retirement of exchangeable bonds	0	(1,842)
Settlement of forward-starting swaps	(2,395)	0
Net proceeds from stock options exercised	5,983	2,212
Net proceeds from issuance of Series H preferred stock	71,427	0
Redemption of Series F preferred stock	(25,000)	0
Retirement of Series B preferred units	(78,800)	0
Net proceeds from issuance of common stock	168,592	63,003
Equity related issuance costs	(591)	0
Contributions from noncontrolling interest	0	3,990
Distributions to noncontrolling interest	(9,667)	(12,337)
Redemptions of noncontrolling interest	(4,019)	(21,065)
Common and preferred stock dividends paid	(67,491)	(60,836)
Net cash provided by financing activities	40,824	21,449
Net decrease in cash and cash equivalents	(4,944)	(12,293)
Cash and cash equivalents at beginning of period	13,753	20,660
Cash and cash equivalents at end of period	8,809	8,367
Supplemental disclosure of cash flow information:
Cash paid for interest, net of $4.5 million and $5.8 million capitalized in 2011 and 2010, respectively	43,594	40,048
Supplemental disclosure of noncash investing and financing activities:
Change in accrual of dividends	1,570	874
Change in value of derivative liabilities	1,836	42,040
Change in unrealized gain of marketable securities	2,283	5,650
Mortgage notes assumed in connection with purchase of real estate including the loan premiums recorded	10,500	12,444
Non-cash contribution from noncontrolling interest	800	0
Change in construction payable	2,041	3,746
Transfer of real estate under development to rental properties	40,784	0
Transfer of real estate under development to co-investments	$ 48,886	$ 0