Acquired Intangible Assets and Liabilities (Summary of Acquired Intangible Assets) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Acquired in-place lease value
Finite-Lived Intangible Assets [Line Items]
Gross amount	$ 1,368,685	$ 1,357,190
Accumulated amortization	(920,682)	(899,071)
Total	448,003	458,119
Customer Relationship Value
Finite-Lived Intangible Assets [Line Items]
Gross amount	3,194,157	1,845,949
Accumulated amortization	(427,337)	(400,570)
Total	2,766,820	1,445,379
Acquired above-market leases
Finite-Lived Intangible Assets [Line Items]
Gross amount	276,679	279,048
Accumulated amortization	(210,646)	(204,233)
Total	66,033	74,815
Below-Market Leases
Finite-Lived Intangible Assets [Line Items]
Gross amount	396,532	396,509
Accumulated amortization	(251,324)	(247,735)
Total	$ 145,208	$ 148,774