Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 83,471	$ 22,629
Adjustments to reconcile net income to net cash provided by operating activities (including discontinued operations):
Depreciation and amortization of building and improvements and leasing costs	122,754	96,971
Increase in provision for bad debts	(192)	141
Depreciation of furniture, fixtures and equipment	896	839
Noncash amortization of share-based compensation awards	5,544	3,365
Noncash amortization of deferred financing costs and debt discounts and premiums	7,078	10,164
Noncash amortization of net (below)/above market rents (Note 3)	(4,616)	1,519
Net gain on dispositions of discontinued operations (Note 13)	(72,809)	(12,555)
Noncash amortization of deferred revenue related to tenant-funded tenant improvements	(6,851)	(7,005)
Straight-line rents	(16,433)	(15,543)
Net change in other operating assets	(2,529)	(4,326)
Net change in other operating liabilities	31,965	18,496
Insurance proceeds received for property damage	(951)	(630)
Net cash provided by operating activities	147,327	114,065
CASH FLOWS FROM INVESTING ACTIVITIES:
Expenditures for acquisition of operating properties, net of cash acquired (Note 2)	(393,133)	(481,756)
Expenditures for acquisition of development properties (Note 2)	(163,271)	0
Expenditures for operating properties	(60,967)	(41,087)
Expenditures for development and redevelopment properties and undeveloped land	(52,937)	(18,682)
Net proceeds received from dispositions of operating properties (Note 13)	141,810	0
Insurance proceeds received for property damage	951	0
Increase in acquisition-related deposits	(8,250)	(11,000)
Increase in restricted cash	(5,526)	(690)
Net cash used in investing activities	(541,323)	(553,215)
CASH FLOWS FROM FINANCING ACTIVITIES:
Net proceeds from issuance of Series G and H preferred stock (Note 7)	192,411	0
Net proceeds from issuance of common stock (Note 7)	662,371	221,015
Borrowings on unsecured line of credit	418,000	302,000
Repayments on unsecured line of credit	(573,000)	(461,000)
Proceeds from issuance of secured debt	97,000	135,000
Principal payments on secured debt	(104,578)	(5,295)
Proceeds from the issuance of unsecured debt (Note 5)	150,000	324,476
Repayments of exchangeable senior notes (Note 5)	(148,000)	0
Financing costs	(5,396)	(8,584)
Decrease in loan deposits	0	2,859
Repurchase of common stock and restricted stock units (Note 9)	(736)	(736)
Proceeds from exercise of stock options	129	395
Dividends and distributions paid to common stockholders and common unitholders	(70,517)	(58,942)
Dividends and distributions paid to preferred stockholders and preferred unitholders	(10,852)	(11,397)
Net cash provided by financing activities	405,332	439,791
Net increase in cash and cash equivalents	11,336	641
Cash and cash equivalents, beginning of period	4,777	14,840
Cash and cash equivalents, end of period	16,113	15,481
SUPPLEMENTAL CASH FLOWS INFORMATION:
Cash paid for interest, net of capitalized interest of $11,531 and $5,361 as of September 30, 2012 and 2011, respectively	49,378	42,070
NONCASH INVESTING TRANSACTIONS:
Accrual for expenditures for operating properties and development and redevelopment properties	8,299	13,506
Tenant improvements funded directly by tenants	16,303	3,037
Assumption of secured debt with property acquisitions (Notes 2 and 5)	177,678	30,042
Assumption of other assets and liabilities with operating and development property acquisitions (Note 2)	11,667	4,515
NONCASH FINANCING TRANSACTIONS:
Accrual of dividends and distributions payable to common stockholders and common unitholders	26,782	21,064
Accrual of dividends and distributions payable to preferred stockholders and preferred unitholders	1,693	1,909
Issuance of share-based compensation awards, net (Note 9)	30,929	7,505
Issuance of common units in the Operating Partnership in connection with an operating property acquisition (Note 2)	5,604	0
Exchange of common units of the Operating Partnership into shares of the Company's common stock	231	91
Series E and Series F Cumulative Redeemable Preferred Stock [Member]
CASH FLOWS FROM FINANCING ACTIVITIES:
Redemption of Series E and Series F preferred stock (Note 7)	(126,500)	0
Series A Preferred Units [Member]
CASH FLOWS FROM FINANCING ACTIVITIES:
Redemption of Series E and Series F preferred stock (Note 7)	$ (75,000)	$ 0