Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Cash flows from operating activities:
Net income	$ 74,010	$ 48,194
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	109,737	109,428
Non-cash compensation expense	11,358	11,856
Income from unconsolidated joint ventures	(11,721)	(7,976)
Distributions of net cash flow from operations of unconsolidated joint ventures	8,972	7,663
Gains from investments in securities	(801)	(373)
Non-cash portion of interest expense	11,839	13,434
Settlement of accreted debt discount on repurchases of unsecured exchangeable senior notes	(68,760)
Gains from early extinguishments of debt	(914)
Gain on forgiveness of debt from discontinued operations	(17,807)
Change in assets and liabilities:
Cash held in escrows	9,359	(7,661)
Tenant and other receivables, net	22,686	6,073
Accrued rental income, net	(19,266)	(20,434)
Prepaid expenses and other assets	6,983	(29,432)
Accounts payable and accrued expenses	1,563	(9,134)
Accrued interest payable	31,073	25,743
Other liabilities	8,883	(5,940)
Tenant leasing costs	(7,933)	(9,157)
Total adjustments	95,251	84,090
Net cash provided by operating activities	169,261	132,284
Cash flows from investing activities:
Acquisitions of real estate	(621,359)	(41,100)
Construction in progress	(93,657)	(64,877)
Building and other capital improvements	(8,613)	(8,874)
Tenant improvements	(34,912)	(14,251)
Deposit on real estate released from escrow		10,000
Issuance of notes receivable	(735)
Capital contributions to unconsolidated joint ventures	(47)	(1,232)
Capital distributions from unconsolidated joint ventures	57
Investments in securities, net	(844)	(695)
Net cash used in investing activities	(760,110)	(121,029)
Cash flows from financing activities:
Repayments of mortgage notes payable	(150,519)	(8,777)
Redemption/repurchase of unsecured exchangeable senior notes	(507,434)
Deferred financing costs	(91)	(676)
Net proceeds from ATM stock issuances	109,330	345,369
Net proceeds from equity transactions	613	3,128
Dividends and distributions	(92,312)	(81,442)
Distributions to noncontrolling interest in property partnership	(750)	(500)
Net cash provided by (used in) financing activities	(641,163)	257,102
Net increase (decrease) in cash and cash equivalents	(1,232,012)	268,357
Cash and cash equivalents, beginning of period	1,823,208	478,948
Cash and cash equivalents, end of period	591,196	747,305
Supplemental disclosures:
Cash paid for interest	140,508	71,213
Interest capitalized	11,201	11,239
Non-cash investing and financing activities:
Additions to real estate included in accounts payable	5,659	8,094
Mortgage note payable assumed in connection with the acquisition of real estate		143,900
Mortgage note payable extinguished through foreclosure	25,000
Real estate transferred upon foreclosure	8,198
Dividends and distributions declared but not paid	92,615	83,019
Conversions of noncontrolling interests to stockholders' equity	6,026	29,216
Conversion of redeemable preferred units to common units	4,115
Issuance of restricted securities to employees and directors	$ 26,139	$ 24,383