Acquired Intangible Assets and Liabilities (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Amortization of customer relationship value, acquired in-place lease value and	$ 76,568	$ 103,934
Customer Relationship Value
Finite-Lived Intangible Assets [Line Items]
Amortization of customer relationship value, acquired in-place lease value and	$ 29,100	38,000
Weighted average remaining contractual life for acquired leases excluding renewals or extensions (in years)	16 years 4 months 24 days
Acquired in-place lease value
Finite-Lived Intangible Assets [Line Items]
Expected average remaining lives (in years)	5 years 10 months 24 days
Amortization of customer relationship value, acquired in-place lease value and	$ 27,200	44,900
Weighted average remaining contractual life for acquired leases excluding renewals or extensions (in years)	5 years 8 months 12 days
Below-Market Leases, Net of Above-Market Leases
Finite-Lived Intangible Assets [Line Items]
Amortization of acquired leases	$ 3,300	$ 6,200
Expected average remaining lives of acquired below market leases (in years)	7 years 8 months 12 days
Expected average remaining lives (in years)	2 years 4 months 24 days