Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash flows from operating activities:
Net income	$ 139,590	$ 57,516	$ 50,782
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on sale of marketable securities	(819)	(4,956)	(12,491)
Gain on remeasurement of co-investment	(21,947)	0	0
Entity's share of gain on the sales of co-investment	(29,112)	(919)	0
Gain on the sales of real estate	(10,870)	(8,562)	0
Loss on early retirement of debt	5,009	1,163	10
Co-investments	1,626	7,929	1,715
Amortization expense	11,644	11,474	4,828
Amortization of discount on notes receivables	(1,832)	(1,757)	(4,806)
Amortization of discount on marketable securities	(5,127)	(4,794)	(3,714)
Loss on derivative instruments - ineffectiveness	0	0	2,301
Depreciation	170,686	152,542	129,711
Equity-based compensation	4,141	2,927	3,251
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(9,488)	(1,172)	(2,771)
Accounts payable and accrued liabilities	12,360	3,620	4,302
Other liabilities	1,638	1,560	2,412
Net cash provided by operating activities	267,499	216,571	175,530
Additions to real estate:
Acquisitions of real estate	(393,771)	(57,478)	(279,607)
Improvements to recent acquisitions	(13,704)	(16,446)	(6,388)
Redevelopment	(40,200)	(45,130)	(14,096)
Revenue generating capital expenditures	(7,620)	(7,616)	(1,584)
Non-revenue generating capital expenditures	(30,491)	(26,090)	(29,278)
Acquisition of and additions to real estate under development	(29,196)	(79,194)	(155,267)
Acquisition of membership interest in co-investment	(85,000)	0	0
Dispositions of real estate	27,800	23,003	0
Changes in restricted cash and refundable deposits	(6,069)	(1,376)	(4,414)
Purchases of marketable securities	(73,735)	(8,048)	(49,974)
Sales and maturities marketable securities	61,703	32,998	102,039
Proceeds from tax investor	0	0	1,223
Purchases of and advances under notes and other receivables	(26,000)	(12,325)	(37,627)
Collections of notes and other receivables	14,525	884	1,855
Contributions to co-investments	(260,153)	(246,106)	(79,450)
Non-operating distributions from co-investments	49,773	17,141	41,700
Net cash used in investing activities	(812,138)	(425,783)	(510,868)
Cash flows from financing activities:
Borrowings under debt agreements	1,745,853	1,514,684	1,214,216
Repayment of debt	(1,371,317)	(1,435,135)	(882,646)
Additions to deferred charges	(6,707)	(5,533)	(4,109)
Payments to settle derivative instruments	0	(2,395)	(81,282)
Retirement of exchangeable bonds	0	0	(5,396)
Net proceeds from issuance of Preferred stock, Series H	0	71,209	0
Retirement of Series B preferred units and Series F Preferred stock	0	(103,800)	0
Equity related issuance cost	(309)	(627)	0
Net proceeds from stock options exercised	2,643	6,986	4,765
Net proceeds from issuance of common stock	357,720	323,931	251,455
Contributions from noncontrolling interest	2,400	0	4,038
Distributions to noncontrolling interest	(16,691)	(16,963)	(24,795)
Redemption of noncontrolling interest	(6,986)	(5,387)	(24,186)
Common and preferred stock dividends paid	(156,250)	(138,622)	(123,629)
Net cash provided by financing activities	550,356	208,348	328,431
Net increase (decrease) in cash and cash equivalents	5,717	(864)	(6,907)
Cash and cash equivalents at beginning of year	12,889	13,753	20,660
Cash and cash equivalents at end of year	18,606	12,889	13,753
Supplemental disclosure of cash flow information:
Cash paid for interest, net of $10,346, $8,240, and $9,486 capitalized in 2012, 2011 and 2010, respectively	95,597	89,691	83,497
Supplemental disclosure of noncash investing and financing activities:
Transfer from real estate under development to rental properties	6,632	165,214	170,940
Transfer from co investments to rental properties	148,053	0	0
Mortgage notes assumed in connection with purchases of real estate including the loan premiums recorded	82,133	20,927	87,336
Transfer from real estate under development to co investments	0	54,472	0
Note receivable settled when the company purchased the property securing the note receivable	0	0	25,750
Contribution of note receivable to co-investment	12,325	0	0
Change in accrual of dividends	5,441	3,206	2,655
Change in fair value of derivative liabilities	4,461	230	1,907
Change in fair value of marketable securities	459	2,836	6,670
Change in construction payable	$ 1,113	$ 2,518	$ 1,304