Acquired Intangible Assets and Liabilities (Summary of Acquired Intangible Assets) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Below-market lease, gross amount	$ 284,695	$ 283,899
Below-market lease, accumulated amortization	(206,054)	(202,000)
Total	78,641	81,899
Acquired in-place lease value
Finite-Lived Intangible Assets [Line Items]
Gross amount	898,904	896,693
Accumulated amortization	(532,545)	(517,443)
Net	366,359	379,250
Tenant relationship value
Finite-Lived Intangible Assets [Line Items]
Gross amount	975,188	971,519
Accumulated amortization	(99,926)	(82,069)
Net	875,262	889,450
Acquired above-market leases
Finite-Lived Intangible Assets [Line Items]
Gross amount	110,748	110,142
Accumulated amortization	(89,922)	(87,961)
Net	$ 20,826	$ 22,181