Segment Reporting (Summary on Revenues and Funds from Operations) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Rental and related revenue	$ 208,957	$ 184,581	$ 616,451	$ 554,752
General contractor and service fee revenue (''Service Operations'')	93,932	127,708	226,507	409,617
Total Segment Revenues	298,735	309,318	836,562	956,150
Consolidated Revenue from continuing operations	302,889	312,289	842,958	964,369
Discontinued Operations	143	50,315	2,987	151,373
Consolidated Revenue	303,032	362,604	845,945	1,115,742
Net earnings excluding depreciation and Non-Segment Items	143,557	128,348	432,588	392,643
Interest expense	(61,539)	(54,528)	(183,623)	(161,765)
Interest and other income	150	172	394	543
Other operating expenses	(130)	(60)	(591)	(171)
General and administrative expenses	(8,934)	(9,493)	(32,367)	(29,231)
Undeveloped land carrying costs	(2,140)	(2,259)	(6,606)	(7,021)
Acquisition-related activity	(954)	(342)	(2,563)	(1,525)
Income tax benefit	103	194	103	194
Other non-segment income	3,278	1,934	4,119	4,456
Net (income) loss attributable to noncontrolling interests - consolidated entities not wholly owned by the Partnership	(59)	(43)	(365)	163
Joint venture items	8,997	11,635	27,999	30,597
Dividends on preferred shares/units	(11,081)	(14,399)	(35,356)	(46,347)
Adjustments for redemption/repurchase of preferred shares/units	0	(3,633)	(5,730)	(3,796)
Discontinued operations	(92)	14,745	17	41,163
FFO of Partnership Attributable To Common Unitholders	71,156	72,271	198,019	219,903
Net (income) loss attributable to noncontrolling interests - common limited partnership interests in the Partnership	459	868	1,736	369
Noncontrolling Interest Share of FFO Adjustments	(1,638)	(2,835)	(5,358)	(6,206)
FFO of General Partner attributable to common shareholders	69,977	70,304	194,397	214,066
Depreciation and amortization on continuing operations	(95,117)	(81,068)	(279,136)	(242,043)
Depreciation and Amortization, Discontinued Operations	(22)	(16,267)	(1,202)	(50,386)
Company's share of joint venture adjustments	(8,782)	(8,531)	(26,008)	(24,798)
Earnings from depreciated property sales on continuing operations	403	(1,437)	245	66,910
Earnings from depreciated property sales on discontinued operations	1,608	2,088	11,179	16,405
Earnings from depreciated property sales - share of joint venture	2,065	0	2,065	91
Noncontrolling Interest Share of FFO Adjustments, Reconciliation Add-Back	1,638	2,835	5,358	6,206
Net income (loss) attributable to common shareholders/unitholders	(28,230)	(32,076)	(93,102)	(13,549)
Add back: Net income (loss) attributable to noncontrolling interests - common limited partnership interests in the Partnership	(459)	(868)	(1,736)	(369)
Net income (loss) attributable to common unitholders	(28,689)	(32,944)	(94,838)	(13,918)
Industrial [Member]
Rental and related revenue	109,400	95,676	327,713	281,083
Net earnings excluding depreciation and Non-Segment Items	81,165	70,214	244,651	203,854
Office [Member]
Rental and related revenue	67,701	66,157	201,606	207,387
Net earnings excluding depreciation and Non-Segment Items	38,302	38,271	117,367	120,999
Medical Office [Member]
Rental and related revenue	23,007	14,292	64,669	41,280
Net earnings excluding depreciation and Non-Segment Items	14,851	8,797	42,344	25,121
Non-reportable Rental Operations segments [Member]
Rental and related revenue	4,695	5,485	16,067	16,783
Net earnings excluding depreciation and Non-Segment Items	3,026	3,905	11,238	12,232
Other Revenue [Member]
Rental and related revenue	4,154	2,971	6,396	8,219
Service Operations [Member]
Net earnings excluding depreciation and Non-Segment Items	$ 6,213	$ 7,161	$ 16,988	$ 30,437