Segment Reporting (Summary on Revenues and Funds from Operations) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Rental and related revenue	$ 205,008	$ 180,009	$ 407,678	$ 370,438
General contractor and service fee revenue (''Service Operations'')	63,607	135,362	132,575	281,909
Total Segment Revenues	267,502	312,106	538,011	647,099
Consolidated Revenue from continuing operations	268,615	315,371	540,253	652,347
Discontinued Operations	664	48,064	2,660	100,791
Consolidated Revenue	269,279	363,435	542,913	753,138
Net earnings excluding depreciation and Non-Segment Items	147,381	132,002	289,158	264,516
Interest expense	(61,220)	(53,814)	(122,138)	(106,461)
Interest and other income	98	284	244	371
Other operating expenses	(196)	(26)	(461)	(111)
General and administrative expenses	(11,594)	(8,541)	(23,433)	(19,738)
Undeveloped land carrying costs	(2,168)	(2,453)	(4,466)	(4,762)
Acquisition-related activity	(1,029)	(594)	(1,609)	(1,183)
Other non-segment income	489	1,541	841	2,522
Net (Income) Loss Attributable to Noncontrolling Interests - consolidated entities not wholly owned by the Partnership	(138)	84	(306)	206
Joint venture items	8,907	10,352	19,002	18,962
Dividends on preferred shares/units	(11,082)	(15,974)	(24,275)	(31,948)
Adjustments for redemption/repurchase of preferred shares/units	0	0	(5,730)	(163)
Discontinued operations	(27)	12,938	36	25,421
FFO of Partnership Attributable To Common Unitholders	69,421	75,799	126,863	147,632
Net (income) loss attributable to noncontrolling interests - common limited partnership interests in the Partnership	466	706	1,277	(499)
Noncontrolling Interest Share of FFO Adjustments	(1,660)	(2,802)	(3,720)	(3,371)
FFO of General Partner attributable to common shareholders	68,227	73,703	124,420	143,762
Depreciation and amortization on continuing operations	(92,721)	(83,351)	(184,084)	(161,057)
Depreciation and amortization on discontinued operations	(222)	(16,762)	(1,115)	(34,037)
Company's share of joint venture adjustments	(8,640)	(8,639)	(17,226)	(16,267)
Earnings from depreciated property sales on continuing operations	119	492	(158)	68,348
Earnings from depreciated property sales on discontinued operations	3,095	2,713	9,571	14,316
Earnings from depreciated property sales - share of joint venture	0	0	0	91
Noncontrolling Interest Share of FFO Adjustments, Reconciliation Add-Back	1,660	2,802	3,720	3,371
Net income (loss) attributable to common shareholders	(28,482)	(29,042)	(64,872)	18,527
Add back: Net income (loss) attributable to noncontrolling interests - common limited partnership interests in the Partnership	(466)	(706)	(1,277)	499
Net income (loss) attributable to common unitholders	(28,948)	(29,748)	(66,149)	19,026
Industrial [Member]
Rental and related revenue	110,257	92,293	218,497	185,673
Net earnings excluding depreciation and Non-Segment Items	83,796	67,524	163,614	133,862
Office [Member]
Rental and related revenue	67,003	65,303	133,905	141,231
Net earnings excluding depreciation and Non-Segment Items	39,827	39,442	79,064	82,727
Medical Office [Member]
Rental and related revenue	20,921	13,503	41,662	26,987
Net earnings excluding depreciation and Non-Segment Items	13,826	8,625	27,493	16,427
Non-reportable Rental Operations segments [Member]
Rental and related revenue	5,714	5,645	11,372	11,299
Net earnings excluding depreciation and Non-Segment Items	4,204	4,018	8,212	8,224
Other Revenue [Member]
Rental and related revenue	1,113	3,265	2,242	5,248
Service Operations [Member]
Net earnings excluding depreciation and Non-Segment Items	$ 5,728	$ 12,393	$ 10,775	$ 23,276