Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
CASH FLOWS FROM OPERATING ACTIVITIES:
Net (Loss) Income	$ (9,190)	$ (221,619)	$ 4,186
Adjustments to Reconcile Net (Loss) Income to Net Cash Provided by Operating Activities:
Depreciation	95,931	104,175	112,241
Amortization of Deferred Financing Costs	3,963	3,473	3,030
Other Amortization	36,390	41,024	52,646
Impairment of Real Estate, Net	(2,661)	194,552	6,934
Provision for Bad Debt	1,110	1,880	3,259
Equity in (Income) Loss of Joint Ventures	(980)	(675)	6,470
Distributions from Joint Venture	1,033	3,032	2,319
Gain on Sale of Real Estate	(21,789)	(11,951)	(24,580)
Gain on Sale of Joint Venture Interests		(11,226)
Gain on Change in Control of Interests	(689)
Loss (Gain) on Retirement of Debt	5,459	4,304	(34,562)
Prepayment Premiums Associated with Retirement of Debt	(1,268)
Mark-to-Market Loss (Gain) on Interest Rate Protection Agreements	1,718	1,107	(3,667)
Decrease in Developments for Sale Costs			812
(Increase) Decrease in Tenant Accounts Receivable, Prepaid Expenses and Other Assets, Net	(2,933)	(1,580)	51,641
Increase in Deferred Rent Receivable	(7,733)	(7,041)	(8,350)
Decrease in Accounts Payable, Accrued Expenses, Other Liabilities, Rents Received in Advance and Security Deposits	(5,684)	(9,411)	(27,631)
Decrease (Increase) in Restricted Cash	117	(15)	7
Payments of Premiums and Discounts Associated with Senior Unsecured Notes	(5,260)	(6,840)	(2,576)
Net Cash Provided by Operating Activities	87,534	83,189	142,179
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of and Additions to Investment in Real Estate and Lease Costs	(90,524)	(89,736)	(75,947)
Net Proceeds from Sales of Investments in Real Estate	75,953	68,046	74,982
Contributions to and Investments in Joint Ventures	(155)	(777)	(3,742)
Distributions and Sale Proceeds from Joint Venture Interests	650	11,519	6,333
Repayments of Notes Receivable	10,394	1,460	3,151
Increase in Lender Escrows	(97)	(435)
Net Cash (Used in) Provided by Investing Activities	(3,779)	(9,923)	4,777
CASH FLOWS FROM FINANCING ACTIVITIES:
Debt and Equity Issuance Costs	(7,162)	(4,544)	(8,322)
Proceeds from the Issuance of Common Stock, Net of Underwriter's Discount	202,845	50,087	84,465
Repurchase and Retirement of Restricted Stock	(1,001)	(298)	(739)
Payments on Interest Rate Swap Agreement	(489)	(450)	(320)
Settlement of Interest Rate Protection Agreements			(7,491)
Repayments on Senior Unsecured Notes	(234,307)	(259,018)	(336,196)
Dividends/Distributions			(12,614)
Preferred Stock Dividends	(15,254)	(19,677)	(20,296)
Repayments on Mortgage and Other Loans Payable	(71,983)	(20,872)	(13,513)
Proceeds from Origination of Mortgage Loans Payable	255,900	105,580	339,783
Proceeds from Unsecured Credit Facility	390,500	69,097	180,000
Repayments on Unsecured Credit Facility	(618,553)	(149,280)	(172,000)
Costs Associated with the Retirement of Debt		(1,008)
Repurchase of Equity Component Exchangeable Notes			(33)
Net Cash (Used in) Provided by Financing Activities	(99,504)	(230,383)	32,724
Net Effect of Exchange Rate Changes on Cash and Cash Equivalents	(61)	137	81
Net (Decrease) Increase in Cash and Cash Equivalents	(15,749)	(157,117)	179,680
Cash and Cash Equivalents, Beginning of Year	25,963	182,943	3,182
Cash and Cash Equivalents, End of Year	$ 10,153	$ 25,963	$ 182,943