Segment Reporting Segment Reporting (Second Generation Capital Expenditures) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting Information [Line Items]
Payments For Second Generation Tenant Improvements Leasing Costs And Building Improvements	$ 63,884	$ 99,264	$ 88,723
Industrial [Member]
Segment Reporting Information [Line Items]
Payments For Second Generation Tenant Improvements Leasing Costs And Building Improvements	33,095	34,872	23,271
Office [Member]
Segment Reporting Information [Line Items]
Payments For Second Generation Tenant Improvements Leasing Costs And Building Improvements	30,092	63,933	65,203
Medical Office [Member]
Segment Reporting Information [Line Items]
Payments For Second Generation Tenant Improvements Leasing Costs And Building Improvements	641	410	183
Non Reportable Rental Operations Segments [Member]
Segment Reporting Information [Line Items]
Payments For Second Generation Tenant Improvements Leasing Costs And Building Improvements	$ 56	$ 49	$ 66