Acquired Intangible Assets and Liabilities (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Finite-Lived Intangible Assets [Line Items]
Amortization of below market leases	$ 2,000	$ 2,400	$ 4,300	$ 4,700
Expected average remaining lives of acquired below market leases (in years)			6 years 9 months
Amortization of intangible assets			$ 89,963	33,830
Acquired above-market leases
Finite-Lived Intangible Assets [Line Items]
Expected average remaining lives (in years)			4 years 2 months 2 days
Acquired in-place lease value
Finite-Lived Intangible Assets [Line Items]
Expected average remaining lives (in years)			8 years 7 days
Amortization of intangible assets	13,300	$ 10,500	$ 27,000	$ 22,100
Weighted average remaining contractual life for acquired leases excluding renewals or extensions (in years)			7 years 5 months 6 days
Tenant relationship value
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	15,900		$ 31,700
Weighted average remaining contractual life for acquired leases excluding renewals or extensions (in years)			10 years 10 months 15 days
Trade name
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 6,400		$ 6,900
Write-down of intangible assets			$ 6,100