Acquired Intangible Assets and Liabilities (Summary of Acquired Intangible Assets) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Acquired in-place lease value
Finite-Lived Intangible Assets [Line Items]
Gross amount	$ 1,375,003	$ 1,357,190
Accumulated amortization	(976,121)	(899,071)
Total	398,882	458,119
Customer Relationship Value
Finite-Lived Intangible Assets [Line Items]
Gross amount	2,938,308	1,845,949
Accumulated amortization	(526,657)	(400,570)
Total	2,411,651	1,445,379
Acquired above-market leases
Finite-Lived Intangible Assets [Line Items]
Gross amount	278,094	279,048
Accumulated amortization	(228,014)	(204,233)
Total	50,080	74,815
Below-Market Leases
Finite-Lived Intangible Assets [Line Items]
Gross amount	398,870	396,509
Accumulated amortization	(263,606)	(247,735)
Total	$ 135,264	$ 148,774