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 (loss)	$ (18,110)	$ 64,789
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of buildings and tenant improvements	63,860	67,063
Amortization of deferred leasing and other costs	28,396	27,918
Amortization of deferred financing costs	3,246	3,644
Straight-line rent adjustment	(5,852)	(6,966)
Earnings from land and depreciated property sales	(6,199)	(79,459)
Third-party construction contracts, net	(1,877)	(13,974)
Other accrued revenues and expenses, net	(43,116)	(42,945)
Operating distributions received in excess of equity in earnings from unconsolidated companies	4,995	7,955
Net cash provided by operating activities	25,343	28,025
Cash flows from investing activities:
Development of real estate investments	(29,639)	(37,318)
Acquisition of real estate investments and related intangible assets	(131,515)	(22,261)
Acquisition of undeveloped land	(12,180)	0
Second generation tenant improvements, leasing costs and building improvements	(15,361)	(17,476)
Other deferred leasing costs	(9,142)	(6,272)
Other assets	502	2,816
Proceeds from land and depreciated property sales, net	63,281	437,494
Capital distributions from unconsolidated companies	0	54,730
Capital contributions and advances to unconsolidated companies, net	(3,521)	(6,068)
Net cash provided by (used for) investing activities	(137,575)	405,645
Cash flows from financing activities:
Proceeds from Issuance of Common Stock	146,969	0
Payments for redemption/repurchase of preferred shares	(168,272)	(2,096)
Payments on unsecured debt	(451)	(42,948)
Payments on secured indebtedness including principal amortization	(10,455)	(3,897)
Borrowings on lines of credit, net	0	(174,717)
Distributions to common shareholders	(43,922)	(42,892)
Distributions to preferred shareholders	(9,467)	(15,974)
Distributions to noncontrolling interests	(1,033)	(1,145)
Deferred financing costs	(206)	(1,270)
Net cash used for financing activities	(86,837)	(284,939)
Net increase (decrease) in cash and cash equivalents	(199,069)	148,731
Cash and cash equivalents at beginning of period	213,809	18,384
Cash and cash equivalents at end of period	14,740	167,115
Non-cash investing and financing activities:
Assumption of indebtedness and other liabilities in real estate acquisitions	19,626	85,955
Contribution of properties to unconsolidated companies	0	52,110
Issuance of Limited Partner Units for acquisition	0	28,357
Preferred distributions declared but not paid	3,726	0
Parent [Member]
Non-cash investing and financing activities:
Conversion of Limited Partner Units to common shares	$ 29,460	$ 933