Acquired Intangible Assets and Liabilities (Summary of Acquired Intangible Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Below-market lease, accumulated amortization	$ (247,735)	$ (242,422)
Acquired in-place lease value
Finite-Lived Intangible Assets [Line Items]
Gross amount	1,357,190	1,569,401
Accumulated amortization	(899,071)	(795,033)
Net	458,119	774,368
Tenant relationship value
Finite-Lived Intangible Assets [Line Items]
Gross amount	1,845,949	2,339,606
Accumulated amortization	(400,570)	(291,818)
Net	1,445,379	2,047,788
Acquired above-market leases
Finite-Lived Intangible Assets [Line Items]
Gross amount	279,048	277,796
Accumulated amortization	(204,233)	(158,037)
Net	74,815	119,759
Acquired below-market leases
Finite-Lived Intangible Assets [Line Items]
Gross amount	396,509	442,535
Accumulated amortization	(247,735)	(242,422)
Net	$ 148,774	$ 200,113