Intangible Assets and Liabilities - Intangible Assets and Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Intangible Assets [Line Items]
Intangible Assets, Total Cost	$ 119,996	$ 123,806
Intangible Assets, Accumulated Amortization	(60,578)	(58,834)
Intangible Assets, net	59,418	64,972
Acquired Lease Intangibles, Net	18,573	20,274
Below market leases [Member]
Intangible Assets [Line Items]
Acquired Lease Intangibles, Gross	35,366	36,213
Acquired Lease Intangibles, Accumulated Amortization	(16,793)	(15,939)
Acquired Lease Intangibles, Net	18,573	20,274
In-place lease value [Member]
Intangible Assets [Line Items]
Intangible Assets, Total Cost	104,705	108,060
Intangible Assets, Accumulated Amortization	(48,495)	(47,003)
Intangible Assets, net	56,210	61,057
Tenant relationship value [Member]
Intangible Assets [Line Items]
Intangible Assets, Total Cost	10,580	11,201
Intangible Assets, Accumulated Amortization	(9,225)	(9,275)
Intangible Assets, net	1,355	1,926
Above market leases acquired [Member]
Intangible Assets [Line Items]
Intangible Assets, Total Cost	4,711	4,545
Intangible Assets, Accumulated Amortization	(2,858)	(2,556)
Intangible Assets, net	$ 1,853	$ 1,989