Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash flows from operating activities:
Net income (loss)	$ (75,868)	$ 96,309	$ 65,262
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation of buildings and tenant improvements	262,825	267,222	271,058
Amortization of deferred leasing and other costs	116,594	118,457	89,126
Amortization of deferred financing costs	13,321	14,530	13,897
Straight-line rent adjustment	(19,546)	(23,877)	(15,233)
Impairment charges	0	12,931	9,834
(Gain) loss on debt extinguishment	0	0	16,349
(Gain) loss on acquisitions	0	(1,057)	(57,715)
Earnings from land and depreciated property sales	(13,811)	(169,431)	(72,716)
Third-party construction contracts, net	(10,837)	(17,352)	(6,449)
Other accrued revenues and expenses, net	13,300	24,001	68,892
Operating distributions received in excess of equity in earnings from unconsolidated companies	13,179	15,804	8,851
Net cash provided by operating activities	299,157	337,537	391,156
Cash flows from investing activities:
Development of real estate investments	(264,755)	(162,070)	(119,404)
Acquisition of real estate investments and related intangible assets, net of cash acquired	(665,527)	(544,816)	(488,539)
Acquisition of undeveloped land	(64,944)	(14,090)	(14,404)
Second generation tenant improvements, leasing costs and building improvements	(63,884)	(99,264)	(88,723)
Other deferred leasing costs	(27,772)	(26,311)	(38,905)
Other assets	4,504	747	(7,260)
Proceeds from land and depreciated property sales, net	138,118	1,572,093	499,520
Capital distributions from unconsolidated companies	5,157	59,252	22,119
Capital contributions and advances to unconsolidated companies	(28,513)	(34,606)	(53,194)
Net cash provided by (used for) investing activities	(967,616)	750,935	(288,790)
Cash flows from financing activities:
Proceeds from issuance of common shares, net	315,295	0	298,004
Payments for redemption/repurchase of preferred shares	(168,272)	(110,726)	(118,787)
Proceeds from Issuance of Unsecured Debt	600,000	0	250,000
Payments on and repurchases of unsecured debt	(222,846)	(334,432)	(392,597)
Proceeds from Secured Notes Payable	13,336	0	4,158
Payments on secured indebtedness including principal amortization	(117,287)	(29,025)	(207,060)
Proceeds from (Repayments of) Lines of Credit	264,707	(172,753)	177,276
Distributions to common shareholders	(181,892)	(171,814)	(162,015)
Distributions to preferred shareholders	(46,438)	(60,353)	(69,468)
Contributions from (distributions to) noncontrolling interests, net	2,179	(5,292)	(5,741)
Buyout of noncontrolling interests	(6,208)	0	0
Increase (Decrease) in Book Overdrafts	45,272	0	0
Deferred financing costs	(9,307)	(8,652)	(5,074)
Net cash provided by (used for) financing activities	488,539	(893,047)	(231,304)
Net increase (decrease) in cash and cash equivalents	(179,920)	195,425	(128,938)
Cash and cash equivalents at beginning of year	213,809	18,384	147,322
Cash and cash equivalents at end of year	33,889	213,809	18,384
Non-cash investing and financing activities:
Assumption of indebtedness and other liabilities in real estate acquisitions	112,754	177,082	527,464
Contribution of properties to, net of debt assumed by, unconsolidated companies	0	53,293	41,609
Investments and advances related to acquisition of previously unconsolidated companies	0	5,987	184,140
Assumption of indebtedness by buyer in real estate dispositions	0	24,914	0
Conversion of Limited Partner Units to common shares	29,213	3,130	(8,055)
Issuance of Limited Partner Units for acquisition	0	28,357	0
Subsidiary of Common Parent [Member]
Cash flows from operating activities:
Net income (loss)	(75,868)	96,309	65,262
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation of buildings and tenant improvements	262,825	267,222	271,058
Amortization of deferred leasing and other costs	116,594	118,457	89,126
Amortization of deferred financing costs	13,321	14,530	13,897
Straight-line rent adjustment	(19,546)	(23,877)	(15,233)
Impairment charges	0	12,931	9,834
(Gain) loss on debt extinguishment	0	0	16,349
(Gain) loss on acquisitions	0	(1,057)	(57,715)
Earnings from land and depreciated property sales	(13,811)	(169,431)	(72,716)
Third-party construction contracts, net	(10,837)	(17,352)	(6,449)
Other accrued revenues and expenses, net	13,399	24,036	68,512
Operating distributions received in excess of equity in earnings from unconsolidated companies	13,179	15,804	8,851
Net cash provided by operating activities	299,256	337,572	390,776
Cash flows from investing activities:
Development of real estate investments	(264,755)	(162,070)	(119,404)
Acquisition of real estate investments and related intangible assets, net of cash acquired	(665,527)	(544,816)	(488,539)
Acquisition of undeveloped land	(64,944)	(14,090)	(14,404)
Second generation tenant improvements, leasing costs and building improvements	(63,884)	(99,264)	(88,723)
Other deferred leasing costs	(27,772)	(26,311)	(38,905)
Other assets	4,504	747	(7,260)
Proceeds from land and depreciated property sales, net	138,118	1,572,093	499,520
Capital distributions from unconsolidated companies	5,157	59,252	22,119
Capital contributions and advances to unconsolidated companies	(28,513)	(34,606)	(53,194)
Net cash provided by (used for) investing activities	(967,616)	750,935	(288,790)
Cash flows from financing activities:
Contributions from the General Partner	315,295	0	298,066
Payments for redemption/repurchase of preferred shares	(168,272)	(110,726)	(118,787)
Proceeds from Issuance of Unsecured Debt	600,000	0	250,000
Payments on and repurchases of unsecured debt	(222,846)	(334,432)	(392,597)
Proceeds from Secured Notes Payable	13,336	0	4,158
Payments on secured indebtedness including principal amortization	(117,287)	(29,025)	(207,060)
Proceeds from (Repayments of) Lines of Credit	264,707	(172,753)	177,276
Distributions to common shareholders	(185,299)	(176,593)	(165,881)
Distributions to preferred shareholders	(46,438)	(60,353)	(69,468)
Contributions from (distributions to) noncontrolling interests, net	5,470	(566)	(1,739)
Buyout of noncontrolling interests	(6,208)	0	0
Increase (Decrease) in Book Overdrafts	45,272	0	0
Deferred financing costs	(9,307)	(8,652)	(5,074)
Net cash provided by (used for) financing activities	488,423	(893,100)	(231,106)
Net increase (decrease) in cash and cash equivalents	(179,937)	195,407	(129,120)
Cash and cash equivalents at beginning of year	213,826	18,419	147,539
Cash and cash equivalents at end of year	33,889	213,826	18,419
Non-cash investing and financing activities:
Assumption of indebtedness and other liabilities in real estate acquisitions	112,754	177,082	527,464
Contribution of properties to, net of debt assumed by, unconsolidated companies	0	53,293	41,609
Investments and advances related to acquisition of previously unconsolidated companies	0	5,987	184,140
Assumption of indebtedness by buyer in real estate dispositions	0	24,914	0
Conversion of Limited Partner Units to common shares	29,213	3,130	(8,055)
Issuance of Limited Partner Units for acquisition	$ 0	$ 28,357	$ 0