Acquired Intangible Assets and Liabilities (Narrative) (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Increase to rental revenues	$ 202,806,000	$ 156,831,000	$ 399,601,000	$ 308,138,000
Acquired in Place Lease Value [Member]
Expected remaining lives (years)			4.5
Costs incurred to renew or extend leases	13,500,000	10,200,000	27,800,000	20,100,000
Weighted average period prior to renewal (years)			3.9
Acquired Below-Market Leases [Member]
Increase to rental revenues	$ 1,900,000	$ 2,400,000	$ 3,700,000	$ 4,700,000
Expected remaining lives (years)			4.8
Acquired Above-Market Leases [Member]
Expected remaining lives (years)			3.6