Acquired Intangible Assets and Liabilities (Narrative) (Details) - USD ($)	3 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Finite-Lived Intangible Assets [Line Items]
Amortization of below market leases		$ 7,500,000	$ 9,300,000	$ 10,000,000
Amortization of intangible assets		$ 180,608,000	105,833,000	82,310,000
Expected average remaining lives of acquired below market leases		8 years 2 days
Acquired in-place lease value
Finite-Lived Intangible Assets [Line Items]
Expected average remaining lives		6 years 5 months 16 days
Amortization of intangible assets		$ 52,600,000	46,200,000	62,200,000
Weighted average remaining contractual life for acquired leases excluding renewals or extensions		6 years 11 months 23 days
Acquired above-market leases
Finite-Lived Intangible Assets [Line Items]
Expected average remaining lives		4 years 1 month 17 days
Tenant relationship value
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets		$ 67,200,000	$ 14,500,000	0
Remaining amortization period			12 years 11 months 24 days
Trade name
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets		$ 6,900,000	$ 400,000	$ 0
Write-down of intangible assets	$ 6,100,000