Segment Reporting Segment Reporting (Second Generation Capital Expenditures) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Payments For Second Generation Tenant Improvements Leasing Costs And Building Improvements	$ 98,821	$ 91,798	$ 63,884
Operating Segments [Member]
Segment Reporting Information [Line Items]
Payments For Second Generation Tenant Improvements Leasing Costs And Building Improvements	98,821	91,798	63,884
Operating Segments [Member] | Industrial [Member]
Segment Reporting Information [Line Items]
Payments For Second Generation Tenant Improvements Leasing Costs And Building Improvements	53,840	41,971	33,095
Operating Segments [Member] | Office Building [Member]
Segment Reporting Information [Line Items]
Payments For Second Generation Tenant Improvements Leasing Costs And Building Improvements	41,124	46,600	30,092
Operating Segments [Member] | Medical Office [Member]
Segment Reporting Information [Line Items]
Payments For Second Generation Tenant Improvements Leasing Costs And Building Improvements	3,131	3,106	641
Operating Segments [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Payments For Second Generation Tenant Improvements Leasing Costs And Building Improvements	$ 726	$ 121	$ 56