Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
Cash flows from operating activities:
Net income (loss)	$ (35,838)	$ 50,931
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation of buildings and tenant improvements	127,482	135,809
Amortization of deferred leasing and other costs	57,717	59,285
Amortization of deferred financing costs	6,526	7,351
Straight-line rent adjustment	(8,870)	(11,887)
Earnings from land and depreciated property sales	(9,413)	(82,664)
Third-party construction contracts, net	(4,371)	(25,658)
Other accrued revenues and expenses, net	(2,251)	263
Operating distributions received in excess of equity in earnings from unconsolidated companies	9,464	10,862
Net cash provided by operating activities	140,446	144,292
Cash flows from investing activities:
Development of real estate investments	(95,192)	(78,645)
Acquisition of real estate investments and related intangible assets	(231,041)	(99,817)
Acquisition of undeveloped land	(33,371)	0
Second generation tenant improvements, leasing costs and building improvements	(30,891)	(41,284)
Other deferred leasing costs	(16,453)	(13,807)
Other assets	4,421	3,149
Proceeds from land and depreciated property sales, net	89,450	498,249
Capital distributions from unconsolidated companies	0	54,730
Capital contributions and advances to unconsolidated companies, net	(16,431)	(16,917)
Net cash provided by (used for) investing activities	(329,508)	305,658
Cash flows from financing activities:
Proceeds from issuance of common shares, net	151,258	0
Payments for redemption/repurchase of preferred shares	(168,272)	(2,096)
Proceeds from Unsecured Debt Issuance	300,000	0
Payments on and repurchases of unsecured debt	(908)	(43,377)
Proceeds from Secured Debt Financings	13,305	0
Payments on secured indebtedness including principal amortization	(102,869)	(7,968)
Borrowings (Payments) on lines of credit, net	0	(174,717)
Dividends/Distributions to common shareholders/unitholders	(89,219)	(85,843)
Dividends/Distributions to preferred shareholders/unitholders	(20,549)	(31,948)
Contributions from (Distributions to) noncontrolling interests, net	3,647	(2,398)
Deferred financing costs	(4,575)	(2,342)
Net cash provided by (used for) financing activities	81,818	(350,689)
Net increase (decrease) in cash and cash equivalents	(107,244)	99,261
Cash and cash equivalents at beginning of period	213,809	18,384
Cash and cash equivalents at end of period	106,565	117,645
Noncash investing and financing activities:
Assumption of indebtedness and other liabilities in real estate acquisitions	20,064	130,474
Contribution of properties to unconsolidated companies	0	52,868
Conversion of Limited Partner Units to common shares	29,008	1,235
Issuance of Limited Partner Units for acquisition	0	28,357
Preferred distributions declared but not paid	3,726	0
Subsidiary of Common Parent [Member]
Cash flows from operating activities:
Net income (loss)	(35,838)	50,931
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation of buildings and tenant improvements	127,482	135,809
Amortization of deferred leasing and other costs	57,717	59,285
Amortization of deferred financing costs	6,526	7,351
Straight-line rent adjustment	(8,870)	(11,887)
Earnings from land and depreciated property sales	(9,413)	(82,664)
Third-party construction contracts, net	(4,371)	(25,658)
Other accrued revenues and expenses, net	(2,227)	264
Operating distributions received in excess of equity in earnings from unconsolidated companies	9,464	10,862
Net cash provided by operating activities	140,470	144,293
Cash flows from investing activities:
Development of real estate investments	(95,192)	(78,645)
Acquisition of real estate investments and related intangible assets	(231,041)	(99,817)
Acquisition of undeveloped land	(33,371)	0
Second generation tenant improvements, leasing costs and building improvements	(30,891)	(41,284)
Other deferred leasing costs	(16,453)	(13,807)
Other assets	4,421	3,149
Proceeds from land and depreciated property sales, net	89,450	498,249
Capital distributions from unconsolidated companies	0	54,730
Capital contributions and advances to unconsolidated companies, net	(16,431)	(16,917)
Net cash provided by (used for) investing activities	(329,508)	305,658
Cash flows from financing activities:
Contributions from the General Partner	151,258	0
Payments for redemption/repurchase of Preferred Units	(168,272)	(2,096)
Proceeds from Unsecured Debt Issuance	300,000	0
Payments on and repurchases of unsecured debt	(908)	(43,377)
Proceeds from Secured Debt Financings	13,305	0
Payments on secured indebtedness including principal amortization	(102,869)	(7,968)
Borrowings (Payments) on lines of credit, net	0	(174,717)
Dividends/Distributions to common shareholders/unitholders	(91,016)	(88,219)
Dividends/Distributions to preferred shareholders/unitholders	(20,549)	(31,948)
Contributions from (Distributions to) noncontrolling interests, net	5,403	(58)
Deferred financing costs	(4,575)	(2,342)
Net cash provided by (used for) financing activities	81,777	(350,725)
Net increase (decrease) in cash and cash equivalents	(107,261)	99,226
Cash and cash equivalents at beginning of period	213,826	18,419
Cash and cash equivalents at end of period	106,565	117,645
Noncash investing and financing activities:
Assumption of indebtedness and other liabilities in real estate acquisitions	20,064	130,474
Contribution of properties to unconsolidated companies	0	52,868
Conversion of Limited Partner Units to common shares	29,008	1,235
Issuance of Limited Partner Units for acquistion	0	28,357
Preferred distributions declared but not paid	$ 3,726	$ 0