Segment Reporting Segment Reporting (Second Generation Capital Expenditures) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Segment Reporting Information [Line Items]
Payments For Second Generation Tenant Improvements Leasing Costs And Building Improvements	$ 99,264	$ 88,723	$ 79,054
Office [Member]
Segment Reporting Information [Line Items]
Payments For Second Generation Tenant Improvements Leasing Costs And Building Improvements	63,933	65,203	64,281
Industrial [Member]
Segment Reporting Information [Line Items]
Payments For Second Generation Tenant Improvements Leasing Costs And Building Improvements	34,872	23,271	13,845
Non Reportable Rental Operations Segments [Member]
Segment Reporting Information [Line Items]
Payments For Second Generation Tenant Improvements Leasing Costs And Building Improvements	$ 459	$ 249	$ 928