Acquired Intangible Assets and Liabilities (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Finite-Lived Intangible Assets [Line Items]
Amortization of below market leases	$ 9,300,000	$ 10,000,000	$ 11,700,000
Amortization of intangible assets	$ 105,833,000	82,310,000	77,872,000
Expected average remaining lives of acquired below market leases	2308 days
Acquired above market leases:
Finite-Lived Intangible Assets [Line Items]
Expected average remaining lives	3 years 8 months
Acquired in place lease value:
Finite-Lived Intangible Assets [Line Items]
Expected average remaining lives	5 years 11 months
Amortization of intangible assets	$ 46,200,000	62,200,000	62,700,000
Weighted average remaining contractual life for acquired leases excluding renewals or extensions	1789 days
Tenant relationship value:
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 14,500,000	0	0
Remaining amortization period	4144 days
Trade name:
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 400,000	$ 0	$ 0
Remaining amortization period	1376 days