Segment Reporting Summary of Net Operating Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Straight line rent adjustments, net	$ 13,743	$ 22,396	$ 19,965
Income (Loss) from Equity Method Investments	47,403	(3,304)	94,317
Gain on dissolution of unconsolidated company	30,697	0	0
Promote income	26,299	0	0
Interest Expense	(141,576)	(173,574)	(196,186)
Depreciation, Depletion and Amortization, Nonproduction	(317,818)	(317,329)	(346,275)
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal	162,093	229,702	162,715
Impairment Charges	(18,018)	(22,932)	(49,106)
Other Nonoperating Income (Expense)	4,035	4,667	1,246
General and Administrative Expense	(55,389)	(58,565)	(49,362)
Gain on land sales	9,865	35,054	10,441
Other Operating Income (Expense), Net	(3,864)	(5,947)	(7,191)
Loss on debt extinguishment	(33,934)	(85,713)	(283)
Acquisition-related activity	7,176	(8,499)	(1,099)
Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest	312,682	185,277	214,746
Operating Segments [Member]
Segment Reporting Information [Line Items]
Property Level Net Operating Income – Cash Basis	549,937	499,220	453,024
Property Level Net Income, Cash Basis, Continuing Operations	577,499	563,651	555,831
Operating Segments [Member] | Industrial [Member]
Segment Reporting Information [Line Items]
Property Level Net Operating Income – Cash Basis	429,239	386,153	347,672
Operating Segments [Member] | Medical Office [Member]
Segment Reporting Information [Line Items]
Property Level Net Operating Income – Cash Basis	114,641	103,540	100,846
Operating Segments [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Property Level Net Operating Income – Cash Basis	6,057	9,527	4,506
Operating Segments [Member] | Service Operations [Member]
Segment Reporting Information [Line Items]
Service Operations Net Income (loss)	8,343	14,197	24,469
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Sold Properties Included in Continuing Operations Net Operating Income	27,562	64,431	102,807
Straight line rent adjustments, net	13,744	20,669	19,412
Gain (Loss) on Contract Termination	1,725	1,567	5,246
Amortization of lease incentives and market rents	(1,526)	(3,258)	(4,789)
Intercompany rents and other adjusting items	(119)	(2,044)	(4,219)
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Income (Loss) from Equity Method Investments	47,403	(3,304)	94,317
Gain on dissolution of unconsolidated company	30,697	0	0
Promote income	26,299	0	0
Interest Expense	(141,576)	(173,574)	(196,186)
Depreciation, Depletion and Amortization, Nonproduction	(317,818)	(317,329)	(346,275)
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal	162,093	229,702	162,715
Impairment Charges	(18,018)	(22,932)	(49,106)
Other Nonoperating Income (Expense)	4,035	4,667	1,246
General and Administrative Expense	(55,389)	(58,565)	(49,362)
Gain on land sales	9,865	35,054	10,441
Other Operating Income (Expense), Net	(3,864)	(5,947)	(7,191)
Loss on debt extinguishment	(33,934)	(85,713)	(283)
Acquisition-related activity	7,176	(8,499)	(1,099)
Other Non-segment Income	$ (3,953)	$ (3,065)	$ (421)