Segment Reporting (Summary on Revenues and Funds from Operations) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Number of Reportable Segments			4
Rental and related revenue	$ 228,883	$ 199,326	$ 668,230	$ 586,570
General contractor and service fee revenue (''Service Operations'')	62,807	93,932	161,004	226,507
Revenues	291,690	293,258	829,234	813,077
Discontinued Operations	3,912	9,774	18,419	32,868
Consolidated Revenue	295,602	303,032	847,653	845,945
Interest expense	(58,100)	(58,812)	(176,005)	(175,726)
Asset impairment charges	0	0	(3,777)	0
Interest and other income, net	145	150	1,219	394
Other operating expenses	(47)	(130)	(150)	(591)
General and administrative expenses	(10,373)	(8,934)	(33,225)	(32,367)
Earnings from sales of land	3,365	0	3,365	0
Undeveloped land carrying costs	(2,108)	(2,140)	(6,837)	(6,606)
Acquisition-related activity	(726)	(954)	(2,506)	(2,563)
Income Tax Benefit	4,500	103	4,500	103
Dividends on preferred shares/units	(7,356)	(11,081)	(24,261)	(35,356)
Adjustments for redemption of preferred shares/units	0	0	(5,932)	(5,730)
FFO Attributable To Common Unitholders of the Partnership	96,810	71,156	257,699	198,019
FFO attributable to common shareholders of the General Partner	95,518	69,977	254,218	194,397
Depreciation and amortization on continuing operations	(103,594)	(90,202)	(296,791)	(264,435)
Depreciation and amortization, discontinued operations	(844)	(4,937)	(6,686)	(15,903)
Gains on depreciated property sales on continuing operations	0	403	1,108	245
Gains on depreciated property sales on discontinued operations	8,441	1,608	101,052	11,179
Gains on depreciated property sales - share of joint venture			49,000
Net income (loss) attributable to common shareholders/unitholders	(6,067)	(28,230)	83,470	(93,102)
Net income (loss) attributable to common unitholders of the Partnership	(6,159)	(28,689)	84,612	(94,838)
Operating Segments [Member]
Revenues	290,105	289,104	825,211	806,681
Net earnings excluding depreciation and Non-Segment Items	158,992	137,771	472,337	413,504
Operating Segments [Member] | Industrial [Member]
Rental and related revenue	123,749	107,345	357,777	321,524
Net earnings excluding depreciation and Non-Segment Items	92,052	79,803	266,044	240,605
Operating Segments [Member] | Office [Member]
Rental and related revenue	66,691	65,290	198,890	194,038
Net earnings excluding depreciation and Non-Segment Items	38,842	37,193	116,385	113,425
Operating Segments [Member] | Medical Office [Member]
Rental and related revenue	35,093	21,108	101,733	59,336
Net earnings excluding depreciation and Non-Segment Items	23,533	13,756	67,976	38,842
Operating Segments [Member] | All Other Segments [Member]
Rental and related revenue	1,765	1,429	5,807	5,276
Net earnings excluding depreciation and Non-Segment Items	1,150	806	3,853	3,644
Operating Segments [Member] | Service Operations [Member]
General contractor and service fee revenue (''Service Operations'')	62,807	93,932	161,004	226,507
Net earnings excluding depreciation and Non-Segment Items	3,415	6,213	18,079	16,988
Corporate, Non-Segment [Member]
Rental and related revenue	1,585	4,154	4,023	6,396
Discontinued Operations	3,912	9,774	18,419	32,868
Interest expense	(58,100)	(58,812)	(176,005)	(175,726)
Asset impairment charges	0	0	(3,777)	0
Interest and other income, net	145	150	1,219	394
Other operating expenses	(47)	(130)	(150)	(591)
General and administrative expenses	(10,373)	(8,934)	(33,225)	(32,367)
Earnings from sales of land	3,365	0	3,365	0
Undeveloped land carrying costs	(2,108)	(2,140)	(6,837)	(6,606)
Acquisition-related activity	(726)	(954)	(2,506)	(2,563)
Income Tax Benefit	4,500	103	4,500	103
Other non-segment income	(32)	3,278	490	4,119
Noncontrolling Interest in Net Income (Loss) Joint Venture Partners, NonRedeemable	(140)	(59)	(487)	(365)
Joint venture items	6,945	8,997	22,212	27,999
Dividends on preferred shares/units	(7,356)	(11,081)	(24,261)	(35,356)
Adjustments for redemption of preferred shares/units	0	0	(5,932)	(5,730)
Discontinued operations	1,745	2,967	6,756	11,204
Net (income) loss attributable to noncontrolling interests - common limited partnership interests in the Partnership	92	459	(1,142)	1,736
Noncontrolling Interest Share of FFO Adjustments	(1,384)	(1,638)	(2,339)	(5,358)
Depreciation and amortization on continuing operations	(103,594)	(90,202)	(296,791)	(264,435)
Depreciation and amortization, discontinued operations	(844)	(4,937)	(6,686)	(15,903)
Company's share of joint venture adjustments	(7,127)	(8,782)	(20,730)	(26,008)
Gains on depreciated property sales on continuing operations	0	403	1,108	245
Gains on depreciated property sales on discontinued operations	8,441	1,608	101,052	11,179
Gains on depreciated property sales - share of joint venture	155	2,065	48,960	2,065
Noncontrolling Interest Share of FFO Adjustments, Reconciliation Add-Back	1,384	1,638	2,339	5,358
Add back: Net income (loss) attributable to noncontrolling interests - common limited partnership interests in the Partnership	$ (92)	$ (459)	$ 1,142	$ (1,736)