Segment Reporting (Summary on Revenues and Funds from Operations) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Number of Reportable Segments			4
Rental and related revenue	$ 224,665	$ 197,213	$ 443,977	$ 392,312
General contractor and service fee revenue (''Service Operations'')	50,793	63,607	98,197	132,575
Revenues	275,458	260,820	542,174	524,887
Discontinued Operations	2,906	8,459	9,877	18,026
Consolidated Revenue	278,364	269,279	552,051	542,913
Interest expense	(59,296)	(59,146)	(118,945)	(118,025)
Asset Impairment Charges	(3,777)	0	(3,777)	0
Interest and other income, net	921	98	1,074	244
Other operating expenses	(35)	(196)	(103)	(461)
General and administrative expenses	(9,707)	(11,594)	(22,852)	(23,433)
Undeveloped land carrying costs	(2,531)	(2,168)	(4,729)	(4,466)
Acquisition-related activity	(2,423)	(1,029)	(1,780)	(1,609)
Dividends on preferred shares/units	(7,355)	(11,082)	(16,905)	(24,275)
Adjustments for redemption of preferred shares/units	0	0	(5,932)	(5,730)
FFO Attributable To Common Unitholders of the Partnership	82,981	69,421	160,889	126,863
FFO attributable to common shareholders of the General Partner	81,866	68,227	158,700	124,420
Depreciation and amortization on continuing operations	(98,545)	(88,667)	(194,801)	(175,953)
Depreciation and Amortization, Discontinued Operations	(714)	(4,276)	(4,238)	(9,246)
Gains on depreciated property sales on continuing operations	940	119	1,108	(158)
Gains on depreciated property sales on discontinued operations	83,657	3,095	92,611	9,571
Gains on depreciated property sales - share of joint venture			48,800
Net income (loss) attributable to common shareholders/unitholders	61,494	(28,482)	89,537	(64,872)
Net income (loss) attributable to common unitholders of the Partnership	62,336	(28,948)	90,771	(66,149)
Operating Segments [Member]
Revenues	274,217	259,707	539,736	522,645
Net earnings excluding depreciation and Non-Segment Items	159,296	142,093	315,858	278,799
Operating Segments [Member] | Industrial [Member]
Rental and related revenue	118,350	108,257	234,226	214,411
Net earnings excluding depreciation and Non-Segment Items	89,289	82,438	174,096	160,943
Operating Segments [Member] | Office [Member]
Rental and related revenue	68,796	66,055	135,168	132,093
Net earnings excluding depreciation and Non-Segment Items	40,530	39,331	78,820	78,026
Operating Segments [Member] | Medical Office [Member]
Rental and related revenue	34,539	19,961	68,104	39,718
Net earnings excluding depreciation and Non-Segment Items	22,785	13,201	45,576	26,216
Operating Segments [Member] | All Other Segments [Member]
Rental and related revenue	1,739	1,827	4,041	3,848
Net earnings excluding depreciation and Non-Segment Items	1,091	1,395	2,702	2,839
Operating Segments [Member] | Service Operations [Member]
General contractor and service fee revenue (''Service Operations'')	50,793	63,607	98,197	132,575
Net earnings excluding depreciation and Non-Segment Items	5,601	5,728	14,664	10,775
Corporate, Non-Segment [Member]
Rental and related revenue	1,241	1,113	2,438	2,242
Discontinued Operations	2,906	8,459	9,877	18,026
Interest expense	(59,296)	(59,146)	(118,945)	(118,025)
Asset Impairment Charges	(3,777)	0	(3,777)	0
Interest and other income, net	921	98	1,074	244
Other operating expenses	(35)	(196)	(103)	(461)
General and administrative expenses	(9,707)	(11,594)	(22,852)	(23,433)
Undeveloped land carrying costs	(2,531)	(2,168)	(4,729)	(4,466)
Acquisition-related activity	(2,423)	(1,029)	(1,780)	(1,609)
Other non-segment income	211	489	522	841
Noncontrolling Interest in Net Income (Loss) Joint Venture Partners, NonRedeemable	(141)	(138)	(347)	(306)
Joint venture items	7,074	8,907	15,267	19,002
Dividends on preferred shares/units	(7,355)	(11,082)	(16,905)	(24,275)
Adjustments for redemption of preferred shares/units	0	0	(5,932)	(5,730)
Discontinued operations	744	3,187	3,538	6,282
Net (income) loss attributable to noncontrolling interests - common limited partnership interests in the Partnership	(842)	466	(1,234)	1,277
Noncontrolling Interest Share of FFO Adjustments	(273)	(1,660)	(955)	(3,720)
Depreciation and amortization on continuing operations	(98,545)	(88,667)	(194,801)	(175,953)
Depreciation and Amortization, Discontinued Operations	(714)	(4,276)	(4,238)	(9,246)
Company's share of joint venture adjustments	(5,974)	(8,640)	(13,603)	(17,226)
Gains on depreciated property sales on continuing operations	940	119	1,108	(158)
Gains on depreciated property sales on discontinued operations	83,657	3,095	92,611	9,571
Gains on depreciated property sales - share of joint venture	(9)	0	48,805	0
Noncontrolling Interest Share of FFO Adjustments, Reconciliation Add-Back	273	1,660	955	3,720
Add back: Net income (loss) attributable to noncontrolling interests - common limited partnership interests in the Partnership	$ 842	$ (466)	$ 1,234	$ (1,277)