Acquired Intangible Assets and Liabilities (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Finite-Lived Intangible Assets [Line Items]
Amortization of below market leases	$ (7,000)	$ (1,900)	$ (13,800)	$ (3,900)
Expected average remaining lives of acquired below market leases (in years)			8 years 5 months 10 days
Amortization of acquired in-place lease value and deferred leasing costs			$ 214,843	90,452
Acquired in-place lease value
Finite-Lived Intangible Assets [Line Items]
Expected average remaining lives (in years)			6 years 3 months
Amortization of acquired in-place lease value and deferred leasing costs	55,100	14,400	$ 112,100	28,600
Weighted average remaining contractual life for acquired leases excluding renewals or extensions (in years)			5 years 8 months 26 days
Tenant relationship value
Finite-Lived Intangible Assets [Line Items]
Amortization of acquired in-place lease value and deferred leasing costs	$ 30,900	$ 17,500	$ 62,000	$ 35,100
Weighted average remaining contractual life for acquired leases excluding renewals or extensions (in years)			14 years 9 months 2 days
Acquired above-market leases
Finite-Lived Intangible Assets [Line Items]
Expected average remaining lives (in years)			3 years 3 months 12 days