Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Cash flows from operating activities:
Net income (loss)	$ (53,387)	$ 36,062
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation of buildings and tenant improvements	193,479	204,134
Amortization of deferred leasing and other costs	86,859	88,295
Amortization of deferred financing costs	9,878	11,070
Straight-line rent adjustment	(15,725)	(19,012)
Earnings from land and depreciated property sales	(11,424)	(83,315)
Third-party construction contracts, net	(4,295)	(18,417)
Other accrued revenues and expenses, net	(14,621)	14,586
Operating distributions received in excess of equity in earnings from unconsolidated companies	10,772	11,681
Net cash provided by operating activities	201,536	245,084
Cash flows from investing activities:
Development of real estate investments	(176,340)	(125,676)
Acquisition of real estate investments and related intangible assets	(321,099)	(179,047)
Acquisition of undeveloped land	(37,166)	(3,825)
Second generation tenant improvements, leasing costs and building improvements	(46,682)	(71,732)
Other deferred leasing costs	(22,727)	(20,950)
Other assets	674	(4,500)
Proceeds from land and depreciated property sales, net	112,559	504,688
Capital distributions from unconsolidated companies	4,890	54,730
Capital contributions and advances to unconsolidated companies, net	(19,262)	(28,362)
Net cash provided by (used for) investing activities	(505,153)	125,326
Cash flows from financing activities:
Proceeds from issuance of common shares, net	236,301	0
Payments for redemption/repurchase of preferred shares/units	(168,272)	(110,726)
Proceeds from unsecured debt issuance	600,000	0
Payments on and repurchases of unsecured debt	(172,374)	(166,346)
Proceeds from secured debt financings	13,305	0
Payments on secured indebtedness including principal amortization	(107,240)	(24,841)
Borrowings (payments) on lines of credit, net	(20,293)	111,247
Dividends/Distributions to common shareholders/unitholders	(135,083)	(128,817)
Dividends/Distributions to preferred shareholders/unitholders	(31,630)	(46,347)
Contributions from (distributions to) noncontrolling interests, net	2,788	(3,952)
Buyout of noncontrolling interests	(6,208)	0
Deferred financing costs	(8,334)	(2,830)
Net cash provided by (used for) financing activities	202,960	(372,612)
Net increase (decrease) in cash and cash equivalents	(100,657)	(2,202)
Cash and cash equivalents at beginning of period	213,809	18,384
Cash and cash equivalents at end of period	113,152	16,182
Noncash investing and financing activities:
Assumption of indebtedness and other liabilities in real estate acquisitions	19,992	150,042
Contribution of properties to unconsolidated companies	0	53,245
Investments and advances related to acquisition of previously unconsolidated companies	0	5,987
Conversion of Limited Partner Units to common shares	29,002	3,052
Issuance of Limited Partner Units for acquistion	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)	(53,387)	36,062
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation of buildings and tenant improvements	193,479	204,134
Amortization of deferred leasing and other costs	86,859	88,295
Amortization of deferred financing costs	9,878	11,070
Straight-line rent adjustment	(15,725)	(19,012)
Earnings from land and depreciated property sales	(11,424)	(83,315)
Third-party construction contracts, net	(4,295)	(18,417)
Other accrued revenues and expenses, net	(14,582)	14,588
Operating distributions received in excess of equity in earnings from unconsolidated companies	10,772	11,681
Net cash provided by operating activities	201,575	245,086
Cash flows from investing activities:
Development of real estate investments	(176,340)	(125,676)
Acquisition of real estate investments and related intangible assets	(321,099)	(179,047)
Acquisition of undeveloped land	(37,166)	(3,825)
Second generation tenant improvements, leasing costs and building improvements	(46,682)	(71,732)
Other deferred leasing costs	(22,727)	(20,950)
Other assets	674	(4,500)
Proceeds from land and depreciated property sales, net	112,559	504,688
Capital distributions from unconsolidated companies	4,890	54,730
Capital contributions and advances to unconsolidated companies, net	(19,262)	(28,362)
Net cash provided by (used for) investing activities	(505,153)	125,326
Cash flows from financing activities:
Contributions from the General Partner	236,301	0
Payments for redemption/repurchase of preferred shares/units	(168,272)	(110,726)
Proceeds from unsecured debt issuance	600,000	0
Payments on and repurchases of unsecured debt	(172,374)	(166,346)
Proceeds from secured debt financings	13,305	0
Payments on secured indebtedness including principal amortization	(107,240)	(24,841)
Borrowings (payments) on lines of credit, net	(20,293)	111,247
Dividends/Distributions to common shareholders/unitholders	(137,662)	(132,423)
Dividends/Distributions to preferred shareholders/unitholders	(31,630)	(46,347)
Contributions from (distributions to) noncontrolling interests, net	5,311	(408)
Buyout of noncontrolling interests	(6,208)	0
Deferred financing costs	(8,334)	(2,830)
Net cash provided by (used for) financing activities	202,904	(372,674)
Net increase (decrease) in cash and cash equivalents	(100,674)	(2,262)
Cash and cash equivalents at beginning of period	213,826	18,419
Cash and cash equivalents at end of period	113,152	16,157
Noncash investing and financing activities:
Assumption of indebtedness and other liabilities in real estate acquisitions	19,992	150,042
Contribution of properties to unconsolidated companies	0	53,245
Investments and advances related to acquisition of previously unconsolidated companies	0	5,987
Conversion of Limited Partner Units to common shares	29,002	3,052
Issuance of Limited Partner Units for acquistion	0	28,357
Preferred distributions declared but not paid	$ 3,726	$ 0