Summary of Significant Accounting Policies (Construction in Progress) (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Construction in Progress [Line Items]
Internal direct construction costs capitalized related to development of properties and land holdings	$ 3,500,000	$ 3,400,000	$ 3,900,000
Interest costs, capitalized during period	2,000,000	10,400,000	8,900,000
Salaries (including bonuses and benefits) capitalized during the period	3,539,000	3,398,000	3,927,000
Development [Member]
Construction in Progress [Line Items]
Salaries (including bonuses and benefits) capitalized during the period	0	2,331,000	1,772,000
Redevelopment [Member]
Construction in Progress [Line Items]
Salaries (including bonuses and benefits) capitalized during the period	0	127,000	398,000
Tenant Improvements [Member]
Construction in Progress [Line Items]
Salaries (including bonuses and benefits) capitalized during the period	$ 3,539,000	$ 940,000	$ 1,757,000