Segment Reporting (Summary on Revenues and Funds from Operations) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Rental and related revenue	$ 834,369,000	$ 742,883,000	$ 669,543,000
General contractor and service fee revenue (''Service Operations'')	275,071,000	521,796,000	515,361,000
Total Segment Revenues	1,102,019,000	1,253,135,000	1,173,810,000
Consolidated Revenue from continuing operations	1,109,440,000	1,264,679,000	1,184,904,000
Discontinued Operations	8,284,000	194,166,000	248,024,000
Consolidated Revenue	1,117,724,000	1,458,845,000	1,432,928,000
Net earnings excluding depreciation and Non-Segment Items	584,064,000	531,174,000	466,435,000
Interest expense	(245,170,000)	(220,455,000)	(186,407,000)
Impairment charges on non-depreciable properties	0	(12,931,000)	(9,834,000)
Interest and other income	514,000	658,000	534,000
Other operating expenses	(633,000)	(1,237,000)	(1,231,000)
General and administrative expenses	(46,424,000)	(43,107,000)	(41,329,000)
Undeveloped land carrying costs	(8,829,000)	(8,934,000)	(9,203,000)
Gains (Losses) on Extinguishment of Debt	0	0	(16,349,000)
Acquisition-related activity	(4,192,000)	(1,188,000)	55,820,000
Income tax benefit	103,000	194,000	1,126,000
Other non-segment income	3,728,000	6,131,000	8,132,000
Net (income) loss attributable to noncontrolling interests - consolidated entities not wholly owned by the Partnership	(382,000)	115,000	185,000
Joint venture items	37,469,000	38,161,000	40,346,000
Dividends on preferred shares	(46,438,000)	(60,353,000)	(69,468,000)
Adjustments for redemption/repurchase of preferred shares	(5,730,000)	(3,796,000)	(10,438,000)
Discontinued Operations	1,905,000	57,687,000	77,056,000
FFO Attributable To Common Unitholders	269,985,000	282,119,000	305,375,000
Net (income) loss attributable to noncontrolling interests - common limited partnership interests in the Partnership	2,273,000	(859,000)	351,000
Noncontrolling interest share of FFO adjustments	(7,054,000)	(6,644,000)	(7,771,000)
FFO attributable to common shareholders	265,204,000	274,616,000	297,955,000
Depreciation and amortization on continuing operations	(375,965,000)	(326,226,000)	(276,045,000)
Depreciation and Amortization, Discontinued Operations	(3,454,000)	(59,453,000)	(84,139,000)
Company's Share Of Joint Venture Related FFO Adjustments	(34,702,000)	(33,687,000)	(34,674,000)
Earnings from depreciated property sales on continuing operations	344,000	68,549,000	39,662,000
Earnings from depreciated property sales on discontinued operations	13,467,000	100,882,000	33,054,000
Earnings from depreciated property sales - share of joint venture	1,907,000	91,000	2,308,000
Noncontrolling interest share of FFO adjustments	7,054,000	6,644,000	7,771,000
Net income (loss) attributable to common shareholders	(126,145,000)	31,416,000	(14,108,000)
Net Income to FFO Reconciliation Net income (loss) attributable to noncontrolling interests - common limited partnership interests in the Partnership	(2,273,000)	859,000	(351,000)
Net Income Loss Attributable To Common Unitholders	(128,418,000)	32,275,000	(14,459,000)
Industrial [Member]
Rental and related revenue	438,525,000	379,030,000	280,538,000
Net earnings excluding depreciation and Non-Segment Items	327,175,000	278,315,000	210,202,000
Office [Member]
Rental and related revenue	267,982,000	272,807,000	313,712,000
Net earnings excluding depreciation and Non-Segment Items	155,456,000	160,530,000	185,914,000
Medical Office [Member]
Rental and related revenue	98,647,000	57,673,000	44,287,000
Net earnings excluding depreciation and Non-Segment Items	65,932,000	35,450,000	28,177,000
Non-reportable Rental Operations segments [Member]
Rental and related revenue	21,794,000	21,829,000	19,912,000
Net earnings excluding depreciation and Non-Segment Items	15,300,000	15,563,000	13,646,000
Other Revenue [Member]
Rental and related revenue	7,421,000	11,544,000	11,094,000
Service Operations [Member]
Net earnings excluding depreciation and Non-Segment Items	$ 20,201,000	$ 41,316,000	$ 28,496,000