Consolidated Statements of Cash Flows (USD $)	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Cash flows from operating activities:
Net income (loss)	$ 113,955,000	$ (35,838,000)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation of buildings and tenant improvements	141,353,000	127,482,000
Amortization of deferred leasing and other costs	57,686,000	57,717,000
Amortization of deferred financing costs	6,867,000	6,526,000
Straight-line rent adjustment	(8,789,000)	(8,870,000)
Asset Impairment Charges	3,777,000	0
Gain on acquisitions	(962,000)	0
Gains on land and depreciated property sales	(93,719,000)	(9,413,000)
Third-party construction contracts, net	8,922,000	(4,371,000)
Other accrued revenues and expenses, net	9,564,000	(2,251,000)
Operating distributions received in excess of (less than) equity in earnings from unconsolidated companies	(40,449,000)	9,464,000
Net cash provided by operating activities	198,205,000	140,446,000
Cash flows from investing activities:
Development of real estate investments	(224,202,000)	(95,192,000)
Acquisition of real estate investments and related intangible assets	(334,287,000)	(231,041,000)
Acquisition of undeveloped land	(23,234,000)	(33,371,000)
Second generation tenant improvements, leasing costs and building improvements	(37,133,000)	(30,891,000)
Other deferred leasing costs	(17,633,000)	(16,453,000)
Other assets	(7,774,000)	4,421,000
Proceeds from land and depreciated property sales, net	259,169,000	89,450,000
Capital distributions from unconsolidated companies	89,237,000	0
Capital contributions and advances to unconsolidated companies	(13,260,000)	(16,431,000)
Net cash provided by (used for) investing activities	(309,117,000)	(329,508,000)
Cash flows from financing activities:
Proceeds from issuance of common shares, net	601,927,000	151,258,000
Payments for redemption of preferred shares/units	(177,955,000)	(168,272,000)
Proceeds from unsecured debt	500,000,000	300,000,000
Payments on unsecured debt	(425,967,000)	(908,000)
Proceeds from secured debt financings	1,933,000	13,305,000
Payments on secured indebtedness including principal amortization	(30,349,000)	(102,869,000)
Borrowings (payments) on line of credit, net	(197,000,000)	0
Dividends/Distributions to common shareholders/unitholders	(109,554,000)	(89,219,000)
Dividends/Distributions to preferred shareholders/unitholders	(16,905,000)	(20,549,000)
Contributions from (distributions to) noncontrolling interests, net	(1,846,000)	3,647,000
Change in book overdrafts	(38,921,000)	0
Deferred financing costs	(6,938,000)	(4,575,000)
Net cash provided by (used for) financing activities	98,425,000	81,818,000
Net increase (decrease) in cash and cash equivalents	(12,487,000)	(107,244,000)
Cash and cash equivalents at beginning of period	33,889,000	213,809,000
Cash and cash equivalents at end of period	21,402,000	106,565,000
Noncash investing and financing activities:
Assumption of indebtedness and other liabilities in real estate acquisitions	106,320,000	20,064,000
Carrying amount of pre-existing ownership interest in acquired property	630,000	0
Conversion of Limited Partner Units to common shares	338,000	29,008,000
Preferred distributions declared but not paid	0	3,726,000
Subsidiary of Common Parent [Member]
Cash flows from operating activities:
Net income (loss)	113,955,000	(35,838,000)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation of buildings and tenant improvements	141,353,000	127,482,000
Amortization of deferred leasing and other costs	57,686,000	57,717,000
Amortization of deferred financing costs	6,867,000	6,526,000
Straight-line rent adjustment	(8,789,000)	(8,870,000)
Asset Impairment Charges	3,777,000	0
Gain on acquisitions	(962,000)	0
Gains on land and depreciated property sales	(93,719,000)	(9,413,000)
Third-party construction contracts, net	8,922,000	(4,371,000)
Other accrued revenues and expenses, net	9,601,000	(2,227,000)
Operating distributions received in excess of (less than) equity in earnings from unconsolidated companies	(40,449,000)	9,464,000
Net cash provided by operating activities	198,242,000	140,470,000
Cash flows from investing activities:
Development of real estate investments	(224,202,000)	(95,192,000)
Acquisition of real estate investments and related intangible assets	(334,287,000)	(231,041,000)
Acquisition of undeveloped land	(23,234,000)	(33,371,000)
Second generation tenant improvements, leasing costs and building improvements	(37,133,000)	(30,891,000)
Other deferred leasing costs	(17,633,000)	(16,453,000)
Other assets	(7,774,000)	4,421,000
Proceeds from land and depreciated property sales, net	259,169,000	89,450,000
Capital distributions from unconsolidated companies	89,237,000	0
Capital contributions and advances to unconsolidated companies	(13,260,000)	(16,431,000)
Net cash provided by (used for) investing activities	(309,117,000)	(329,508,000)
Cash flows from financing activities:
Contributions from the General Partner	601,927,000	151,258,000
Payments for redemption of preferred shares/units	(177,955,000)	(168,272,000)
Proceeds from unsecured debt	500,000,000	300,000,000
Payments on unsecured debt	(425,967,000)	(908,000)
Proceeds from secured debt financings	1,933,000	13,305,000
Payments on secured indebtedness including principal amortization	(30,349,000)	(102,869,000)
Borrowings (payments) on line of credit, net	(197,000,000)	0
Dividends/Distributions to common shareholders/unitholders	(111,088,000)	(91,016,000)
Dividends/Distributions to preferred shareholders/unitholders	(16,905,000)	(20,549,000)
Contributions from (distributions to) noncontrolling interests, net	(349,000)	5,403,000
Change in book overdrafts	(38,921,000)	0
Deferred financing costs	(6,938,000)	(4,575,000)
Net cash provided by (used for) financing activities	98,388,000	81,777,000
Net increase (decrease) in cash and cash equivalents	(12,487,000)	(107,261,000)
Cash and cash equivalents at beginning of period	33,889,000	213,826,000
Cash and cash equivalents at end of period	21,402,000	106,565,000
Noncash investing and financing activities:
Assumption of indebtedness and other liabilities in real estate acquisitions	106,320,000	20,064,000
Carrying amount of pre-existing ownership interest in acquired property	630,000	0
Conversion of Limited Partner Units to common shares	338,000	29,008,000
Preferred distributions declared but not paid	$ 0	$ 3,726,000