Intangible Assets and Liabilities - Intangible Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Intangible Assets [Line Items]
Intangible Assets, Total Cost	$ 117,647	$ 123,806
Intangible Assets, Accumulated Amortization	(62,508)	(58,834)
Intangible Assets, net	55,139	64,972
Acquired Lease Intangibles, Net	17,680	20,274
Below market leases [Member]
Intangible Assets [Line Items]
Acquired Lease Intangibles, Gross	34,523	36,213
Acquired Lease Intangibles, Accumulated Amortization	(16,843)	(15,939)
Acquired Lease Intangibles, Net	17,680	20,274
In-place lease value [Member]
Intangible Assets [Line Items]
Intangible Assets, Total Cost	103,339	108,060
Intangible Assets, Accumulated Amortization	(51,072)	(47,003)
Intangible Assets, net	52,267	61,057
Tenant relationship value [Member]
Intangible Assets [Line Items]
Intangible Assets, Total Cost	9,597	11,201
Intangible Assets, Accumulated Amortization	(8,420)	(9,275)
Intangible Assets, net	1,177	1,926
Above market leases acquired [Member]
Intangible Assets [Line Items]
Intangible Assets, Total Cost	4,711	4,545
Intangible Assets, Accumulated Amortization	(3,016)	(2,556)
Intangible Assets, net	$ 1,695	$ 1,989