Acquired Intangible Assets and Liabilities (Summary of Acquired Intangible Assets) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Below-market lease, gross amount	$ 286,649	$ 294,791
Below-market lease, accumulated amortization	(199,761)	(193,677)
Total	86,888	101,114
Acquired in-place lease value
Finite-Lived Intangible Assets [Line Items]
Gross amount	904,027	901,381
Accumulated amortization	(506,390)	(472,933)
Net	397,637	428,448
Tenant relationship value
Finite-Lived Intangible Assets [Line Items]
Gross amount	943,341	734,800
Accumulated amortization	(64,296)	(14,495)
Net	879,045	720,305
Trade name
Finite-Lived Intangible Assets [Line Items]
Gross amount	7,300	7,300
Accumulated amortization	(7,300)	(417)
Net	0	6,883
Acquired above-market leases
Finite-Lived Intangible Assets [Line Items]
Gross amount	111,965	122,311
Accumulated amortization	(87,411)	(89,613)
Net	$ 24,554	$ 32,698