Acquired Intangible Assets and Liabilities (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Finite-Lived Intangible Assets [Line Items]
Amortization of below market leases	$ 1,400		$ 2,200	$ 5,700	$ 6,900
Expected average remaining lives of acquired below market leases (in years)				6 years 7 months
Amortization of intangible assets				$ 135,252	51,112
Acquired above-market leases
Finite-Lived Intangible Assets [Line Items]
Expected average remaining lives (in years)				4 years 3 months 2 days
Acquired in-place lease value
Finite-Lived Intangible Assets [Line Items]
Expected average remaining lives (in years)				7 years 8 months 7 days
Amortization of intangible assets	13,000		$ 10,100	$ 40,000	$ 32,200
Weighted average remaining contractual life for acquired leases excluding renewals or extensions (in years)				7 years 1 month 1 day
Tenant relationship value
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	18,100			$ 49,800
Weighted average remaining contractual life for acquired leases excluding renewals or extensions (in years)				12 years 5 months 15 days
Trade name
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 0			$ 6,900
Write-down of intangible assets		$ 6,100