Acquired Intangible Assets And Liabilities (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Finite-Lived Intangible Assets [Line Items]
Increase to rental revenues	$ 820,711,000	$ 682,026,000	$ 507,545,000
Acquired In Place Lease Value [Member]
Finite-Lived Intangible Assets [Line Items]
Expected remaining lives (years)	6.3
Costs incurred to renew or extend leases	52,700,000	49,700,000
Weighted average period prior to renewal or extend (years)	5.3
Acquired Below Market Lease Value [Member]
Finite-Lived Intangible Assets [Line Items]
Increase to rental revenues	$ 7,900,000	$ 8,300,000
Expected remaining lives (years)	6.4
Acquired Above Market Lease Value [Member]
Finite-Lived Intangible Assets [Line Items]
Expected remaining lives (years)	4.3