Acquired Intangible Assets and Liabilities (Summary of Acquired Intangible Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Acquired in-place lease value
Finite-Lived Intangible Assets [Line Items]
Gross amount	$ 1,569,401	$ 1,473,515
Accumulated amortization	(795,033)	(613,948)
Net	774,368	859,567
Tenant relationship value
Finite-Lived Intangible Assets [Line Items]
Gross amount	2,339,606	1,978,277
Accumulated amortization	(291,818)	(169,919)
Net	2,047,788	1,808,358
Acquired above-market leases
Finite-Lived Intangible Assets [Line Items]
Gross amount	277,796	294,514
Accumulated amortization	(158,037)	(110,139)
Net	119,759	184,375
Acquired below-market leases
Finite-Lived Intangible Assets [Line Items]
Gross amount	442,535	469,119
Accumulated amortization	(242,422)	(219,654)
Net	$ 200,113	$ 249,465