Segment Reporting Summary of Net Operating Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Straight line rent adjustments, net	$ 22,396	$ 19,965	$ 14,633
Income (Loss) from Equity Method Investments	(3,304)	94,317	54,116
Interest Expense	(173,574)	(196,186)	(202,174)
Depreciation, Depletion and Amortization, Nonproduction	(317,329)	(346,275)	(353,456)
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal	229,702	162,715	59,179
Impairment Charges	(22,932)	(49,106)	(3,777)
Other Nonoperating Income (Expense)	4,667	1,246	1,887
General and Administrative Expense	(58,565)	(49,362)	(42,673)
Gain on land sales	35,054	10,441	9,547
Other Operating Income (Expense), Net	(5,947)	(7,191)	(8,144)
Loss on debt extinguishment	(85,713)	(283)	(9,433)
Acquisition-related activity	(8,499)	(1,099)	(3,093)
Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest	185,277	214,746	54,422
Operating Segments [Member]
Segment Reporting Information [Line Items]
Property Level Net Operating Income – Cash Basis	535,680	487,380	425,577
Property Level Net Income, Cash Basis, Continuing Operations	563,651	555,831	517,181
Operating Segments [Member] | Industrial [Member]
Segment Reporting Information [Line Items]
Property Level Net Operating Income – Cash Basis	393,909	351,955	315,846
Operating Segments [Member] | Medical Office [Member]
Segment Reporting Information [Line Items]
Property Level Net Operating Income – Cash Basis	103,540	91,099	70,844
Operating Segments [Member] | Office Building [Member]
Segment Reporting Information [Line Items]
Property Level Net Operating Income – Cash Basis	38,231	39,820	38,977
Operating Segments [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Property Level Net Operating Income – Cash Basis	0	4,506	(90)
Operating Segments [Member] | Service Operations [Member]
Segment Reporting Information [Line Items]
Service Operations Net Income (loss)	14,197	24,469	22,763
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Sold Properties Included in Continuing Operations Net Operating Income	27,971	68,451	91,604
Straight line rent adjustments, net	20,669	19,412	11,443
Gain (Loss) on Contract Termination	1,567	5,246	11,151
Amortization of lease incentives and market rents	(3,258)	(4,789)	(8,115)
Intercompany rents and other adjusting items	(2,044)	(4,219)	(3,009)
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Income (Loss) from Equity Method Investments	(3,304)	94,317	54,116
Interest Expense	(173,574)	(196,186)	(202,174)
Depreciation, Depletion and Amortization, Nonproduction	(317,329)	(346,275)	(353,456)
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal	229,702	162,715	59,179
Impairment Charges	(22,932)	(49,106)	(3,777)
Other Nonoperating Income (Expense)	4,667	1,246	1,887
General and Administrative Expense	(58,565)	(49,362)	(42,673)
Gain on land sales	35,054	10,441	9,547
Other Operating Income (Expense), Net	(5,947)	(7,191)	(8,144)
Loss on debt extinguishment	(85,713)	(283)	(9,433)
Acquisition-related activity	(8,499)	(1,099)	(3,093)
Other Non-segment Income	$ (3,065)	$ (421)	$ 1,029