Acquired Intangible Assets and Liabilities (Summary of Acquired Intangible Assets) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Acquired in-place lease value
Finite-Lived Intangible Assets [Line Items]
Gross amount	$ 1,369,391	$ 1,357,190
Accumulated amortization	(947,948)	(899,071)
Total	421,443	458,119
Customer Relationship Value
Finite-Lived Intangible Assets [Line Items]
Gross amount	2,884,655	1,845,949
Accumulated amortization	(480,114)	(400,570)
Total	2,404,541	1,445,379
Acquired above-market leases
Finite-Lived Intangible Assets [Line Items]
Gross amount	276,626	279,048
Accumulated amortization	(219,091)	(204,233)
Total	57,535	74,815
Below-Market Leases
Finite-Lived Intangible Assets [Line Items]
Gross amount	396,842	396,509
Accumulated amortization	(256,991)	(247,735)
Total	$ 139,851	$ 148,774