Consolidated Statements of Cash Flows (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Cash flows from operating activities:
Net income (loss)	$ 44,123,000	$ (18,110,000)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation of buildings and tenant improvements	70,548,000	63,860,000
Amortization of deferred leasing and other costs	29,232,000	28,396,000
Amortization of deferred financing costs	3,507,000	3,246,000
Straight-line rent adjustment	(4,839,000)	(5,852,000)
Gain on acquisitions	(962,000)	0
Gains on land and depreciated property sales	(9,122,000)	(6,199,000)
Third-party construction contracts, net	11,138,000	(1,877,000)
Other accrued revenues and expenses, net	(26,261,000)	(43,116,000)
Operating distributions received in excess of (less than) equity in earnings from unconsolidated companies	(43,930,000)	4,995,000
Net cash provided by operating activities	73,434,000	25,343,000
Cash flows from investing activities:
Development of real estate investments	(103,684,000)	(29,639,000)
Acquisition of real estate investments and related intangible assets	(35,495,000)	(131,515,000)
Acquisition of undeveloped land	(5,149,000)	(12,180,000)
Second generation tenant improvements, leasing costs and building improvements	(17,119,000)	(15,361,000)
Other deferred leasing costs	(11,079,000)	(9,142,000)
Other assets	(5,124,000)	502,000
Proceeds from land and depreciated property sales, net	61,931,000	63,281,000
Capital distributions from unconsolidated companies	89,237,000	0
Capital contributions and advances to unconsolidated companies	(4,846,000)	(3,521,000)
Net cash provided by (used for) investing activities	(31,328,000)	(137,575,000)
Cash flows from financing activities:
Proceeds from issuance of common shares, net	574,685,000	146,969,000
Payments for redemption of preferred shares/units	(177,955,000)	(168,272,000)
Proceeds from unsecured debt issuance	250,000,000	0
Payments on unsecured debt	(480,000)	(451,000)
Proceeds from secured debt financings	1,933,000	0
Payments on secured indebtedness including principal amortization	(17,486,000)	(10,455,000)
Borrowings (payments) on line of credit, net	(285,000,000)	0
Dividends/Distributions to common shareholders/unitholders	(54,678,000)	(43,922,000)
Dividends/Distributions to preferred shareholders/unitholders	(9,550,000)	(9,467,000)
Contributions from (distributions to) noncontrolling interests, net	(961,000)	(1,033,000)
Change in book overdrafts	(45,272,000)	0
Deferred financing costs	(4,064,000)	(206,000)
Net cash provided by (used for) financing activities	231,172,000	(86,837,000)
Net increase (decrease) in cash and cash equivalents	273,278,000	(199,069,000)
Cash and cash equivalents at beginning of period	33,889,000	213,809,000
Cash and cash equivalents at end of period	307,167,000	14,740,000
Noncash investing and financing activities:
Assumption of indebtedness and other liabilities in real estate acquisitions	50,000	19,626,000
Carrying amount of pre-existing ownership interest in acquired property	630,000	0
Conversion of Limited Partner Units to common shares	337,000	29,460,000
Preferred distributions declared but not paid	0	3,726,000
Subsidiary of Common Parent [Member]
Cash flows from operating activities:
Net income (loss)	44,123,000	(18,110,000)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation of buildings and tenant improvements	70,548,000	63,860,000
Amortization of deferred leasing and other costs	29,232,000	28,396,000
Amortization of deferred financing costs	3,507,000	3,246,000
Straight-line rent adjustment	(4,839,000)	(5,852,000)
Gain on acquisitions	(962,000)	0
Gains on land and depreciated property sales	(9,122,000)	(6,199,000)
Third-party construction contracts, net	11,138,000	(1,877,000)
Other accrued revenues and expenses, net	(26,232,000)	(43,109,000)
Operating distributions received in excess of (less than) equity in earnings from unconsolidated companies	(43,930,000)	4,995,000
Net cash provided by operating activities	73,463,000	25,350,000
Cash flows from investing activities:
Development of real estate investments	(103,684,000)	(29,639,000)
Acquisition of real estate investments and related intangible assets	(35,495,000)	(131,515,000)
Acquisition of undeveloped land	(5,149,000)	(12,180,000)
Second generation tenant improvements, leasing costs and building improvements	(17,119,000)	(15,361,000)
Other deferred leasing costs	(11,079,000)	(9,142,000)
Other assets	(5,124,000)	502,000
Proceeds from land and depreciated property sales, net	61,931,000	63,281,000
Capital distributions from unconsolidated companies	89,237,000	0
Capital contributions and advances to unconsolidated companies	(4,846,000)	(3,521,000)
Net cash provided by (used for) investing activities	(31,328,000)	(137,575,000)
Cash flows from financing activities:
Contributions from the General Partner	574,685,000	146,969,000
Payments for redemption of preferred shares/units	(177,955,000)	(168,272,000)
Proceeds from unsecured debt issuance	250,000,000	0
Payments on unsecured debt	(480,000)	(451,000)
Proceeds from secured debt financings	1,933,000	0
Payments on secured indebtedness including principal amortization	(17,486,000)	(10,455,000)
Borrowings (payments) on line of credit, net	(285,000,000)	0
Dividends/Distributions to common shareholders/unitholders	(55,458,000)	(44,902,000)
Dividends/Distributions to preferred shareholders/unitholders	(9,550,000)	(9,467,000)
Contributions from (distributions to) noncontrolling interests, net	(210,000)	(77,000)
Change in book overdrafts	(45,272,000)	0
Deferred financing costs	(4,064,000)	(206,000)
Net cash provided by (used for) financing activities	231,143,000	(86,861,000)
Net increase (decrease) in cash and cash equivalents	273,278,000	(199,086,000)
Cash and cash equivalents at beginning of period	33,889,000	213,826,000
Cash and cash equivalents at end of period	307,167,000	14,740,000
Noncash investing and financing activities:
Assumption of indebtedness and other liabilities in real estate acquisitions	50,000	19,626,000
Carrying amount of pre-existing ownership interest in acquired property	630,000	0
Conversion of Limited Partner Units to common shares	337,000	29,460,000
Preferred distributions declared but not paid	$ 0	$ 3,726,000